Dawkins on Kimura
Tim Tyler
``Darwinian selection remains the only explanation for adaptive
evolution - and it is arguable (I would argue) that most if not
all the evolutionary changes we actually see in the macroscopic
world (as opposed to those concealed among the molecules) are
adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
I'm not sure about the "all" but I'm inclined to agree with the "most".
Drift may have something to say about small populations on islands
around speciation events - but it's probably a bit player in most
other places - as far as the *features* of organisms go (as opposed
to the makeup of their genes).
--
__________
|im |yler http://timtyler.org/ t...@tt1lock.org Remove lock to reply.
Guy Hoelzer
wrote on 2/22/04 10:56 PM:
> Another quotable bit:
>
> ``Darwinian selection remains the only explanation for adaptive
> evolution - and it is arguable (I would argue) that most if not
> all the evolutionary changes we actually see in the macroscopic
> world (as opposed to those concealed among the molecules) are
> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
IMHO, if Dawkins and his followers continue to ignore the overwhelming
evidence of adaptive "evolution" in complex dynamical systems that seemingly
lack the basic ingredients for the process of natural selection (e.g.,
populations of reproducing agents), they will look increasingly like
closed-minded zealots as time goes on. At this point, I think it is absurd
and telling that Dawkins begins his argument with such a false premise as
"Darwinian selection remains the only explanation for adaptive evolution."
> I'm not sure about the "all" but I'm inclined to agree with the "most".
>
> Drift may have something to say about small populations on islands
> around speciation events - but it's probably a bit player in most
> other places - as far as the *features* of organisms go (as opposed
> to the makeup of their genes).
Is this all just a gut feeling on your part? That would be fine. I just
want to know if there is any reason your assertion should be persuasive to
others.
Cheers,
Guy
Tim Tyler
> > Another quotable bit:
> >
> > ``Darwinian selection remains the only explanation for adaptive
> > evolution - and it is arguable (I would argue) that most if not
> > all the evolutionary changes we actually see in the macroscopic
> > world (as opposed to those concealed among the molecules) are
> > adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
>
> IMHO, if Dawkins and his followers continue to ignore the overwhelming
> evidence of adaptive "evolution" in complex dynamical systems that seemingly
> lack the basic ingredients for the process of natural selection (e.g.,
> populations of reproducing agents), they will look increasingly like
> closed-minded zealots as time goes on. At this point, I think it is absurd
> and telling that Dawkins begins his argument with such a false premise as
> "Darwinian selection remains the only explanation for adaptive evolution."
I can't really make out what you are on about here.
It seems as though you are asserting that "populations of reproducing
agents" "lack the basic ingredients for the process of natural selection".
That doesn't seem to make much sense.
Or maybe you are saying that evolution (of a sort) can occur in some
systems which "lack the basic ingredients for the process of natural
selection". I guess that is true in theory - e.g. if you have a
hypothetical system - where agents all reproduce at the same rate - and
have no phenotype and can't influence their own copying rate in any way,
then evolution will occur solely by drift. I'm not sure where Dawkins'
views come in, though.
> > I'm not sure about the "all" but I'm inclined to agree with the "most".
> >
> > Drift may have something to say about small populations on islands
> > around speciation events - but it's probably a bit player in most
> > other places - as far as the *features* of organisms go (as opposed
> > to the makeup of their genes).
>
> Is this all just a gut feeling on your part? That would be fine. I just
> want to know if there is any reason your assertion should be persuasive to
> others.
Drift is most effective when population sizes are small. Selection
is most effective when population sizes are large. I reckon this fact
(in conjunction with nature's population sizes) will often limit's drift's
usefulness as an explanation for features of organisms.
dkomo
>
> Another quotable bit:
>
> ``Darwinian selection remains the only explanation for adaptive
> evolution - and it is arguable (I would argue) that most if not
> all the evolutionary changes we actually see in the macroscopic
> world (as opposed to those concealed among the molecules) are
> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
>
> I'm not sure about the "all" but I'm inclined to agree with the "most".
>
> Drift may have something to say about small populations on islands
> around speciation events - but it's probably a bit player in most
> other places - as far as the *features* of organisms go (as opposed
> to the makeup of their genes).
Really? You mean the fact that people have brown, green, or blue
eyes, are short or tall, fat or skinny, beautiful or ugly, have red,
black or blonde hair, are prone to get different diseases in old age,
have different reactions to medications, have different physical
abilities like being able to run for long distances, sing very well,
be really strong, and so on and so on -- these are all the result of
adaptations and natural selection?
Wow.
Tim Tyler
> Tim Tyler wrote:
Drift and selecion are theories of *evolutionary change*.
You are just talking about variation.
There can be as much variation in a population you like without
the structure of the population changing over time.
Also, merely pointing out the existence of variation in a
trait does not demonstrate it is neutral (or near enough
neutral to be subject to drift) - since:
* there is such a thing as frequency-dependent selection;
* most of the members of the population will not be
long-term ancestors - and any variation they exhibit
is of pretty low relevance;
The second point grows in force when you take a gene's eye view.
Of your examples, I would identify the best one as "eye colour".
There /may/ be a case that eye colour is the subject of drift.
***If*** so, eye colour would be one of the things I classified
as a "minor feature".
However I am not convinced that eye colour is anywhere remotely
*near* neutral.
It seems likely to be involved with sexual selection - and the
existence of variation in it can be explained adaptively by the
hypothesis that those with unusual iris colours tend to be
preferred mates.
Further, there is geographic variation in the trait - which
suggests to me adaptation as a sun-shield.
If eye colour is *not* significantly under the influence of selection,
how come nature has chosen bright pure pigments for the irises of the
eyes of many people's in northern regions - while ensuring a hefty
dark melanin pigment in those whose ancestors lived closest to the
equator and were most exposed to the sun?
In summary, I think there are plenty of signs that iris colouration is
strongly adaptive.
Where is the evidence that the spectrum of iris colourations observed
in human populations is due to drift?
Anon.
hte selective pressures will be different. Add into the mix variation
in the environment (which can help maintain polymorphism), and
disruptive selection, we have plenty of adaptive explanations for the
diversity we see.
Of course, drift may also be an explanation, but I believe that we can
only separate out the contributions of the different causes empirically.
Bob
--
Bob O'Hara
Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax: +358-9-191 22 779
WWW: http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
Jeffrey Turner
> Drift is most effective when population sizes are small. Selection
> is most effective when population sizes are large. I reckon this fact
> (in conjunction with nature's population sizes) will often limit's drift's
> usefulness as an explanation for features of organisms.
What is "drift"? Genes mutate randomly, malign mutations die out,
mutations that have no effect on an organism don't really matter and
beneficial mutations propagate and supplant organisms without that
mutation. This generally leads to a new species, in time. But what's
"drift"?
--Jeff
--
Ho, ho, ho, hee, hee, hee
and a couple of ha, ha, has;
That's how we pass the day away,
in the merry old land of Oz.
Tim Tyler
> Of course, drift may also be an explanation, but I believe that we can
> only separate out the contributions of the different causes empirically.
It may be hard to do - but should be possible in principle:
If you used a large population and "stirred" it well, the effects of
drift would become very small compared to selection.
You could similarly create circumstances that emphasised drift - small
populations - with death striking young individuals at random.
These sorts of experiments or observations should - in principle - have
the power to tease out the effects of drift and selection empirically -
and distinguish between hypotheses about to what extent the forces
contribute to the forms of organisms.
In theory, drift can help populations escape local maxima that selection
would leave them stuck on. Quantifying that effect seems like an
important task for the participants in the drift vs selection debate.
Larry Moran
<bob....@SOD.OFF.Spammers.helsinki.fi> wrote:
> dkomo wrote:
>> Tim Tyler wrote:
[snip]
>>>Drift may have something to say about small populations on islands
>>>around speciation events - but it's probably a bit player in most
>>>other places - as far as the *features* of organisms go (as opposed
>>>to the makeup of their genes).
>>
>> Really? You mean the fact that people have brown, green, or blue
>> eyes, are short or tall, fat or skinny, beautiful or ugly, have red,
>> black or blonde hair, are prone to get different diseases in old age,
>> have different reactions to medications, have different physical
>> abilities like being able to run for long distances, sing very well,
>> be really strong, and so on and so on -- these are all the result of
>> adaptations and natural selection?
>>
> Why not? Their ancestors have experienced different environments, so
> hte selective pressures will be different. Add into the mix variation
> in the environment (which can help maintain polymorphism), and
> disruptive selection, we have plenty of adaptive explanations for the
> diversity we see.
>
> Of course, drift may also be an explanation, but I believe that we can
> only separate out the contributions of the different causes empirically.
Yes. Until we can actually test the hypotheses it's wise not to *assume*
that all morphological features are adaptations, don't you think?
Tim seems to be making the default assumption that most morphological
features are due to natural selection. Dawkins certainly makes that
assumption. Is this valid?
Larry Moran
dkomo
Bah! Sounds like panadaptationism. See my reply to Tim Tyler.
We have plenty of "just so" stories to explain each and every
purported adaptation. Any amateur evolution theorist can come up with
half a dozen armchair explanations for each such trait. What we don't
have in most cases is empirical proof that a particular feature of an
organisn is indeed an adaptation to the environment.
> Of course, drift may also be an explanation, but I believe that we can
> only separate out the contributions of the different causes empirically.
>
It may be that many features of organisms are incidental and play no
role in their evolution. That doesn't necessarily imply that these
features are subject to drift. Drift is a phenomenon of small,
isolated populations.
dkomo
That's what I'm getting at. Drift and selection are not the only
alternatives. It's possible to have *no* selection and *no* drift (if
the population is large). The allele frequencies will remain constant
according to the Hardy-Weinberg Law.
> Also, merely pointing out the existence of variation in a
> trait does not demonstrate it is neutral (or near enough
> neutral to be subject to drift) - since:
>
Neither does pointing out the existence of a trait demonstrate that it
is an adaptation that occurred in the past. People who believe that
most or all features of organisms have been selected for are known as
"panadaptationists." Dawkins is certainly one. Gould certainly was
not. I was under the impression that panadaptationism is frowned upon
these days by most evolutionists.
I think many of the traits I pointed out are either what Gould called
"spandrels":
http://spandrel.com/about.html
or they are neutral mutations that have persisted within human
populations for a very long time. They are *not* adaptations to
anything.
> * there is such a thing as frequency-dependent selection;
> * most of the members of the population will not be
> long-term ancestors - and any variation they exhibit
> is of pretty low relevance;
>
> The second point grows in force when you take a gene's eye view.
>
> Of your examples, I would identify the best one as "eye colour".
>
> There /may/ be a case that eye colour is the subject of drift.
>
Why does it have to be the subject of drift? It could simply be an
allele which is not under selection and whose frequency remains pretty
constant in a particular human subpopulation.
> ***If*** so, eye colour would be one of the things I classified
> as a "minor feature".
>
> However I am not convinced that eye colour is anywhere remotely
> *near* neutral.
>
> It seems likely to be involved with sexual selection - and the
> existence of variation in it can be explained adaptively by the
> hypothesis that those with unusual iris colours tend to be
> preferred mates.
>
> Further, there is geographic variation in the trait - which
> suggests to me adaptation as a sun-shield.
>
> If eye colour is *not* significantly under the influence of selection,
> how come nature has chosen bright pure pigments for the irises of the
> eyes of many people's in northern regions - while ensuring a hefty
> dark melanin pigment in those whose ancestors lived closest to the
> equator and were most exposed to the sun?
>
> In summary, I think there are plenty of signs that iris colouration is
> strongly adaptive.
>
It could be. I'm not the diametric opposite of a panadaptationist, as
one well known poster to this group is, but I do insist that the
burden of proof lies with those who claim that particular traits are
adaptations. You made an argument about eye color, but you don't have
any empirical proof. And this, unfortunately, is the case with most
features of organisms. We simply have no direct proof that they are
in fact adaptations, even though we accept the principles of variation
and selection.
> Where is the evidence that the spectrum of iris colourations observed
> in human populations is due to drift?
False dichotomy. It's not selection *or* drift (or even both
operating at the same time). Iris colourations could simply be neural
traits that are subject to neither, being in Hardy-Weinberg
equilibrium.
Larry Moran
Tim Tyler <t...@tt1lock.org> wrote:
[snip]
> Where is the evidence that the spectrum of iris colourations observed
> in human populations is due to drift?
It's probably hidden in the same place as the evidence that it's due
to natural selection.
Larry Moran
Guy Hoelzer
wrote on 2/23/04 7:53 PM:
> Guy Hoelzer <hoe...@unr.edu> wrote or quoted:
>> in article c1c862$p3u$1...@darwin.ediacara.org, Tim Tyler at t...@tt1lock.org
>
>>> Another quotable bit:
>>>
>>> ``Darwinian selection remains the only explanation for adaptive
>>> evolution - and it is arguable (I would argue) that most if not
>>> all the evolutionary changes we actually see in the macroscopic
>>> world (as opposed to those concealed among the molecules) are
>>> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
>>
>> IMHO, if Dawkins and his followers continue to ignore the overwhelming
>> evidence of adaptive "evolution" in complex dynamical systems that seemingly
>> lack the basic ingredients for the process of natural selection (e.g.,
>> populations of reproducing agents), they will look increasingly like
>> closed-minded zealots as time goes on. At this point, I think it is absurd
>> and telling that Dawkins begins his argument with such a false premise as
>> "Darwinian selection remains the only explanation for adaptive evolution."
>
> I can't really make out what you are on about here.
Sorry. My argument got drowned out by my anti-Dawkins rant.
> It seems as though you are asserting that "populations of reproducing
> agents" "lack the basic ingredients for the process of natural selection".
>
> That doesn't seem to make much sense.
Nor I. It is not what I meant to say. What I meant was that natural
selection is a mechanism of adaptive evolution exhibited by "populations of
reproducing agents", but no justification has ever been offered AFAIK for
the position that it is the only possible mechanism in this context. Now
that it is clear that optimizing, adaptive processes occur in all sorts of
contexts, manifesting an array of mechanisms, I think the view espoused by
Dawkins above is no longer tenable.
> Or maybe you are saying that evolution (of a sort) can occur in some
> systems which "lack the basic ingredients for the process of natural
> selection".
Yes. This is part of my view.
> I guess that is true in theory - e.g. if you have a
> hypothetical system - where agents all reproduce at the same rate - and
> have no phenotype and can't influence their own copying rate in any way,
> then evolution will occur solely by drift. I'm not sure where Dawkins'
> views come in, though.
Right. This is all fine, but off the point and not what I meant to say. My
point was that natural selection is not the only possible adaptive process.
>>> I'm not sure about the "all" but I'm inclined to agree with the "most".
>>>
>>> Drift may have something to say about small populations on islands
>>> around speciation events - but it's probably a bit player in most
>>> other places - as far as the *features* of organisms go (as opposed
>>> to the makeup of their genes).
>>
>> Is this all just a gut feeling on your part? That would be fine. I just
>> want to know if there is any reason your assertion should be persuasive to
>> others.
>
> Drift is most effective when population sizes are small. Selection
> is most effective when population sizes are large. I reckon this fact
> (in conjunction with nature's population sizes) will often limit's drift's
> usefulness as an explanation for features of organisms.
You must also be making an implicit assumption about the typical strength of
selection in natural populations, because drift operates in all finite
populations of any size. In other words, drift can dominate weak selection
in large populations, and even strong selection in small populations (e.g.
mutational meltdown). The balance between the influences of drift an
selection was explored explicitly in Ota's Nearly Neutral model.
So what is the basis for your expectation that selection is usually strong
enough to relegate drift to being a "bit player" in natural populations?
Cheers,
Guy
Tim Tyler
> Tim Tyler wrote:
> > dkomo <dkomo...@cris.com> wrote or quoted:
> > > Tim Tyler wrote:
> > > > Drift may have something to say about small populations on islands
> > > > around speciation events - but it's probably a bit player in most
> > > > other places - as far as the *features* of organisms go (as opposed
> > > > to the makeup of their genes).
> > >
> > > Really? You mean the fact that people have brown, green, or blue
> > > eyes, are short or tall, fat or skinny, beautiful or ugly, have red,
> > > black or blonde hair, are prone to get different diseases in old age,
> > > have different reactions to medications, have different physical
> > > abilities like being able to run for long distances, sing very well,
> > > be really strong, and so on and so on -- these are all the result of
> > > adaptations and natural selection?
> >
> > Drift and selecion are theories of *evolutionary change*.
> > You are just talking about variation.
> >
> > There can be as much variation in a population you like without
> > the structure of the population changing over time.
>
> That's what I'm getting at. Drift and selection are not the only
> alternatives. It's possible to have *no* selection and *no* drift (if
> the population is large). The allele frequencies will remain constant
> according to the Hardy-Weinberg Law.
Large populations slow down - but don't eliminate - drift.
You only get no drift in an infinite population - and then it makes
no sense to talk about gene frequencies at all.
> > Also, merely pointing out the existence of variation in a
> > trait does not demonstrate it is neutral (or near enough
> > neutral to be subject to drift) - since:
>
> Neither does pointing out the existence of a trait demonstrate that it
> is an adaptation that occurred in the past.
Of course.
> People who believe that most or all features of organisms have been
> selected for are known as "panadaptationists."
Genetic drift is enough to indicate than not all features of organisms
have necessarily been selected for.
Attributing "most" things to selection seems quite reasonable to me,
though.
> I was under the impression that panadaptationism is frowned upon
> these days by most evolutionists.
Adaptations are certainly all over the place.
"Panadaptationism" is - or ought to mean "adaptations everywhere" -
but exactly how common that is supposed to mean isn't clear.
The word doesn't seem to be in the dictionary - has anyone actually
bothered to define it - or is it just a term of derision?
> I think many of the traits I pointed out are either what Gould called
> "spandrels":
>
> http://spandrel.com/about.html
>
> or they are neutral mutations that have persisted within human
> populations for a very long time. They are *not* adaptations to
> anything.
Most of your traits were statements about the existence of variation
within in a trait.
You mentioned: brown, green, or blue eyes, being short or tall, being
fat or skinny, being beautiful or ugly, having red, black or blonde hair -
and so on.
I've discussed eye colour already. Height is an adaptive trait -
perhaps with some frequency dependent selection for different
heights being caused by the existence of different lifestyles.
Similarly with weight. Also, a fair bit of the observed variation
in both traits is not genetic at all.
Beauty is adaptive - and being ugly is mal-adaptive - and exists through
being constantly generated - and not yet having been weeded out. Hair
colour is also adaptive. Black hair protects against UV radiation - and
that's why all African types have black hair (except a few albinos who
soon get ill). Red and blond hair are (I claim) clearly the result
of sexual selection - just as blue and green eyes have been.
> > * there is such a thing as frequency-dependent selection;
> > * most of the members of the population will not be
> > long-term ancestors - and any variation they exhibit
> > is of pretty low relevance;
> >
> > The second point grows in force when you take a gene's eye view.
> >
> > Of your examples, I would identify the best one as "eye colour".
> >
> > There /may/ be a case that eye colour is the subject of drift.
>
> Why does it have to be the subject of drift? It could simply be an
> allele which is not under selection and whose frequency remains pretty
> constant in a particular human subpopulation.
If the population is finite, it will drift.
> > ***If*** so, eye colour would be one of the things I classified
> > as a "minor feature".
> >
> > However I am not convinced that eye colour is anywhere remotely
> > *near* neutral.
> >
> > It seems likely to be involved with sexual selection - and the
> > existence of variation in it can be explained adaptively by the
> > hypothesis that those with unusual iris colours tend to be
> > preferred mates.
> >
> > Further, there is geographic variation in the trait - which
> > suggests to me adaptation as a sun-shield.
> >
> > If eye colour is *not* significantly under the influence of selection,
> > how come nature has chosen bright pure pigments for the irises of the
> > eyes of many people's in northern regions - while ensuring a hefty
> > dark melanin pigment in those whose ancestors lived closest to the
> > equator and were most exposed to the sun?
> >
> > In summary, I think there are plenty of signs that iris colouration is
> > strongly adaptive.
>
> It could be. I'm not the diametric opposite of a panadaptationist, as
> one well known poster to this group is, but I do insist that the
> burden of proof lies with those who claim that particular traits are
> adaptations.
Hmm. It seems to me that whenever I get into a discussion there's
always someone who claims that the burden of proof lies on my side.
Nine times out of ten I can't see why that is the case - and this
is one of them.
I suggest "adaptation" should *normally* be the default hypothesis -
because adaptation has shown itself to be the best, most powerful
theory for accounting for the forms of organisms.
That's not to say that it's responsible for *everything* - but
that - if anything - the burden of proof ought to normally be
on the drift side of the fence - since drift typically hasn't
been shown to be responsible for very much of anything.
> You made an argument about eye color, but you don't have
> any empirical proof.
...but I could soon find some on request. The dark eyes of african
populations is a well known fact - and has no explanation under the
hypothesis that iris colour is subject to drift.
I might have more problem supporting a sexual selection theory for
eye colour being adaptive, though ;-)
Frequency-dependent selection favouring rare eye colours has
been demonstrated in Drosophila melanogaster - I believe - in:
``Minority mating advantage of certain eye color mutants of Drosophila
melanogaster. IV. Female discrimination among three genotypes.''
- http://calorierestriction.org/pmid/?n=3115250
...but this just demonstrates that the idea is plausible - not that
it is responsible for the observed human variation.
John Edser
> Dawkins quote:
> ``Darwinian selection remains the only explanation for adaptive
> evolution - and it is arguable (I would argue) that most if not
> all the evolutionary changes we actually see in the macroscopic
> world (as opposed to those concealed among the molecules) are
> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
GH:-
IMHO, if Dawkins and his followers continue to ignore the overwhelming
evidence of adaptive "evolution" in complex dynamical systems that seemingly
lack the basic ingredients for the process of natural selection (e.g.,
populations of reproducing agents), they will look increasingly like
closed-minded zealots as time goes on. At this point, I think it is absurd
and telling that Dawkins begins his argument with such a false premise as
"Darwinian selection remains the only explanation for adaptive evolution."
JE:-
Darwinian selection _does_ remain the only _testable_
explanation for adaptive evolution. However, Dawkins
et al have NOT represented the Darwinian argument, they
have only represented the Hamiltonian argument which is
competitive to the Darwinian argument. It is entirely incorrect
to suggest that gene centric Neo Darwinism somehow represents
Darwin's original theory of evolution by natural selection.
The Hamiltonian argument fails because empirically, genes
only have a _dependent_ fitness. What are they entirely
fitness dependent on? The Darwinian _fertile_ organism
level of selection. Hamilton _artificially_ split the
single Darwinian fertile organism level into two independent
levels within just an over simplified model allowing just
a hypothetical gene level of selection to compete and win
against the empirical Darwinian level forcing organism
fitness altruism. Hamilton's model deleted all genetic
epistasis whereas the Darwinian argument included it.
> I'm not sure about the "all" but I'm inclined to agree with the "most".
> Drift may have something to say about small populations on islands
> around speciation events - but it's probably a bit player in most
> other places - as far as the *features* of organisms go (as opposed
> to the makeup of their genes).
GH:-
Is this all just a gut feeling on your part? That would be fine. I just
want to know if there is any reason your assertion should be persuasive to
others.
JE:-
Sampling error is just a random event. This being the case,
it can only be validly supposed to cause temporal variation
and not evolution. Once you allow sampling error as causative
to evolution within evolutionary theory, you reduce this theory
to a non testable status. The testability of evolution by
Darwinian natural selection is not removed if sampling error
is regarded as either random or non random _variation_ because
variation is not causative to evolution it is just one of many
limiting factors within the Darwinian theory of evolution.
Regards,
John Edser
Independent Researcher
PO Box 266
Church Pt
NSW 2105
Australia
phillip smith
wrote on 25/2/04 9:57 AM:
> If eye colour is *not* significantly under the influence of selection,
> how come nature has chosen bright pure pigments for the irises of the
> eyes of many people's in northern regions - while ensuring a hefty
> dark melanin pigment in those whose ancestors lived closest to the
> equator and were most exposed to the sun?
>
> In summary, I think there are plenty of signs that iris colouration is
> strongly adaptive
The genetics of eye colour are not yet well understood
http://www.athro.com/evo/gen/inherit1.html#uncertainty
But even if there is selection for eye colour. Which genes contribute to
that phenotype is probably the result of a kind of genetic drift unless the
population contained all possible mutations that could contribute to to the
desired phenotype at the same time. That is, for selection of the sequence
that was best at giving the brown eye colour phenotype, to occur.
The population would have to be infinite. Selection acts on phenotype, the
neutral theory applies to genotype.
--
Phillip Smith
phi...@buggger.co.nz replace bugger with ihug
http://www.applied-evolution.co.nz
"he who is smeared with blubber has the kindest heart" -- a Greenland Eskimo
adage
Anon.
> Tim Tyler wrote:
>
<snip>
> Why does it have to be the subject of drift? It could simply be an
> allele which is not under selection and whose frequency remains pretty
> constant in a particular human subpopulation.
>
>
>>Where is the evidence that the spectrum of iris colourations observed
>>in human populations is due to drift?
>
>
> False dichotomy. It's not selection *or* drift (or even both
> operating at the same time). Iris colourations could simply be neural
> traits that are subject to neither, being in Hardy-Weinberg
> equilibrium.
>
still believe that it's a good model of reality?
In this particular case, the fact that the population is finite (and the
sub-populations are smaller) means that drift WILL occur. It's just a
fact of life (and death). And it's difficult to see how you can have a
polymorphism without one of the two acting at some stage.
Anon.
dismiss them. But there may be occasions when making that assumption
does lead to further enlightenment. It seems to be a problem of
scientific rhetoric.
Hmm. I'm not sure whether I answered you or not.
> Tim seems to be making the default assumption that most morphological
> features are due to natural selection. Dawkins certainly makes that
> assumption. Is this valid?
>
Well, it's valid. Is it correct? My feeling is that it is, but if
someone show me evidence that it isn't, then I'll change my mind.
Tim Tyler
> Tim Tyler at t...@tt1lock.org wrote on 25/2/04 9:57 AM:
> > If eye colour is *not* significantly under the influence of selection,
> > how come nature has chosen bright pure pigments for the irises of the
> > eyes of many people's in northern regions - while ensuring a hefty
> > dark melanin pigment in those whose ancestors lived closest to the
> > equator and were most exposed to the sun?
> >
> > In summary, I think there are plenty of signs that iris colouration is
> > strongly adaptive
>
> The genetics of eye colour are not yet well understood
> http://www.athro.com/evo/gen/inherit1.html#uncertainty
> But even if there is selection for eye colour. Which genes contribute to
> that phenotype is probably the result of a kind of genetic drift unless the
> population contained all possible mutations that could contribute to to the
> desired phenotype at the same time. That is, for selection of the sequence
> that was best at giving the brown eye colour phenotype, to occur.
> The population would have to be infinite. Selection acts on phenotype, the
> neutral theory applies to genotype.
That doesn't seem to make any sense. This bit:
"for selection of the sequence that was best at giving the brown eye
colour phenotype, to occur. The population would have to be infinite.''
...and this bit:
"Which genes contribute to that phenotype is probably the result of a
kind of genetic drift unless the population contained all possible
mutations that could contribute to to the desired phenotype at the same
time."
...don't add up as arguments. Can you say what you mean more clearly?
Anon.
point is that we know that spatial and temporal variation in selection
pressures occurs, so we can't rule them out just because we don't like
them. Examining their effects is difficult (I've looked at both. One
study needed a 60 year time seies, the other merely a crossing
experiment with a couple of thousand frogs).
>
>>Of course, drift may also be an explanation, but I believe that we can
>>only separate out the contributions of the different causes empirically.
>>
>
>
> It may be that many features of organisms are incidental and play no
> role in their evolution. That doesn't necessarily imply that these
> features are subject to drift. Drift is a phenomenon of small,
> isolated populations.
>
And there are a lot of them about, even in organisms like insects.
Anon.
SBT anyone? There's been a lot of discussion about this (its called the
Shifting Balance Theory). The problem is that the theory is so complex
that it's difficult to show all the bits working at the same time. My
own opinion is that SBT probably isn't very important, because if it
was, we would have plenty of examples of it by now. Scientific, huh?
R.Schenck
> dkomo <dkomo...@cris.com> wrote or quoted:
> > Tim Tyler wrote:
> > > dkomo <dkomo...@cris.com> wrote or quoted:
> > > > Tim Tyler wrote:
> > People who believe that most or all features of organisms have been
> > selected for are known as "panadaptationists."
>
> Genetic drift is enough to indicate than not all features of organisms
> have necessarily been selected for.
>
> Attributing "most" things to selection seems quite reasonable to me,
> though.
>
> > I was under the impression that panadaptationism is frowned upon
> > these days by most evolutionists.
>
> Adaptations are certainly all over the place.
>
> "Panadaptationism" is - or ought to mean "adaptations everywhere" -
> but exactly how common that is supposed to mean isn't clear.
seems to mean what you indicated it ought to mean, adaptations
everywhere. Every trait is the result of adaptation (or at least
primarily/dominantly the result of adaptation). Seems to be an
endpoint on a spectrum. I can't imagine anyone is an acutal
panadaptationist, but dawkin's certainly can safely be refered to as
one. How about Ultra-darwinian; seems to imply the same thing?
>
> The word doesn't seem to be in the dictionary - has anyone actually
> bothered to define it - or is it just a term of derision?
probably in as much as 'big bang' was intended to be insulting.
>
> > I think many of the traits I pointed out are either what Gould called
> > "spandrels":
> >
> > http://spandrel.com/about.html
> >
> > or they are neutral mutations that have persisted within human
> > populations for a very long time. They are *not* adaptations to
> > anything.
>
> Most of your traits were statements about the existence of variation
> within in a trait.
>
> You mentioned: brown, green, or blue eyes, being short or tall, being
> fat or skinny, being beautiful or ugly, having red, black or blonde hair -
> and so on.
>
> I've discussed eye colour already. Height is an adaptive trait -
> perhaps with some frequency dependent selection for different
> heights being caused by the existence of different lifestyles.
> Similarly with weight. Also, a fair bit of the observed variation
> in both traits is not genetic at all.
>
> Beauty is adaptive - and being ugly is mal-adaptive - and exists through
> being constantly generated - and not yet having been weeded out. Hair
> colour is also adaptive. Black hair protects against UV radiation - and
> that's why all African types have black hair (except a few albinos who
> soon get ill). Red and blond hair are (I claim) clearly the result
> of sexual selection - just as blue and green eyes have been.
>
but certainly you wouldn't claim that all traits are adaptive. As far
as the 'major' features of evolution being adaptive, well thats a
different story and i think its what you mean by 'most' traits.
> > > * there is such a thing as frequency-dependent selection;
> > > * most of the members of the population will not be
> > > long-term ancestors - and any variation they exhibit
> > > is of pretty low relevance;
> > >
> > > The second point grows in force when you take a gene's eye view.
> > >
> > > Of your examples, I would identify the best one as "eye colour".
> > >
> > > There /may/ be a case that eye colour is the subject of drift.
> >
> > Why does it have to be the subject of drift? It could simply be an
> > allele which is not under selection and whose frequency remains pretty
> > constant in a particular human subpopulation.
>
> If the population is finite, it will drift.
>
also, how is an allele not subject to selection -not- going to drift?
> > > ***If*** so, eye colour would be one of the things I classified
> > > as a "minor feature".
> > >
> > > However I am not convinced that eye colour is anywhere remotely
> > > *near* neutral.
> > >
> > > It seems likely to be involved with sexual selection - and the
> > > existence of variation in it can be explained adaptively by the
> > > hypothesis that those with unusual iris colours tend to be
> > > preferred mates.
> > >
> > > Further, there is geographic variation in the trait - which
> > > suggests to me adaptation as a sun-shield.
> > >
> > > If eye colour is *not* significantly under the influence of selection,
> > > how come nature has chosen bright pure pigments for the irises of the
> > > eyes of many people's in northern regions - while ensuring a hefty
> > > dark melanin pigment in those whose ancestors lived closest to the
> > > equator and were most exposed to the sun?
> > >
I'll just respond to this here instead of in the original post.
ettiqute schmettiquite.
i think the dark eye colour can be considered the default. As far as
bright eye colour, even if all northern pops had this trait (say blue
in one pop, green in another, but i don't think this is even strictly
true) then why green in one and blue in the other? Either way it
seems historical accident/constraint is going to be involved. Except
for sexual selection, that of course is something of a different
issue, not completly but something different anyways.
> > > In summary, I think there are plenty of signs that iris colouration is
> > > strongly adaptive.
> >
> > It could be. I'm not the diametric opposite of a panadaptationist, as
> > one well known poster to this group is, but I do insist that the
> > burden of proof lies with those who claim that particular traits are
> > adaptations.
>
> Hmm. It seems to me that whenever I get into a discussion there's
> always someone who claims that the burden of proof lies on my side.
>
> Nine times out of ten I can't see why that is the case - and this
> is one of them.
>
> I suggest "adaptation" should *normally* be the default hypothesis -
> because adaptation has shown itself to be the best, most powerful
> theory for accounting for the forms of organisms.
>
> That's not to say that it's responsible for *everything* - but
> that - if anything - the burden of proof ought to normally be
> on the drift side of the fence - since drift typically hasn't
> been shown to be responsible for very much of anything.
>
how about no default either way?
> > You made an argument about eye color, but you don't have
> > any empirical proof.
>
> ...but I could soon find some on request. The dark eyes of african
> populations is a well known fact - and has no explanation under the
> hypothesis that iris colour is subject to drift.
>
why would the eye colour change simply because of drift tho? If it
was, then one could look at say pops where dark eyes are dominant, put
corrective surgery and glasses (heck even sunglasses) and whatnot
eliminates whatever advantage dark eyes might've had formerly. Do
those pops show evidence torwards more variation in eye colour? If
not, well there wouldn't be much info there, but if they did, that
would be interesting.
snip
R.Schenck
> in article c1ehrf$1el9$1...@darwin.ediacara.org, Tim Tyler at t...@tt1lock.org
> wrote on 2/23/04 7:53 PM:
>
> > Guy Hoelzer <hoe...@unr.edu> wrote or quoted:
> >> in article c1c862$p3u$1...@darwin.ediacara.org, Tim Tyler at t...@tt1lock.org
>
> >>> Another quotable bit:
> >>>
> >>> ``Darwinian selection remains the only explanation for adaptive
> >>> evolution - and it is arguable (I would argue) that most if not
> >>> all the evolutionary changes we actually see in the macroscopic
> >>> world (as opposed to those concealed among the molecules) are
> >>> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
> > I guess that is true in theory - e.g. if you have a
> > hypothetical system - where agents all reproduce at the same rate - and
> > have no phenotype and can't influence their own copying rate in any way,
> > then evolution will occur solely by drift. I'm not sure where Dawkins'
> > views come in, though.
>
> Right. This is all fine, but off the point and not what I meant to say. My
> point was that natural selection is not the only possible adaptive process.
what other adpative process is there? i understand that drift is
useful for 'adaptive peaks and valleys' and all, but even then its
selection that is the over-riding factor. Or are you saying that
selection is merely not the only mechanism/force/player whatever
involved?
snip
dkomo
>
> Tim Tyler wrote:
>
> > Drift is most effective when population sizes are small. Selection
> > is most effective when population sizes are large. I reckon this fact
> > (in conjunction with nature's population sizes) will often limit's drift's
> > usefulness as an explanation for features of organisms.
>
> What is "drift"? Genes mutate randomly, malign mutations die out,
> mutations that have no effect on an organism don't really matter and
> beneficial mutations propagate and supplant organisms without that
> mutation. This generally leads to a new species, in time. But what's
> "drift"?
>
> --Jeff
>
>From a post to talk.origins on Sept 5, 2002:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Subject: Neutral evolution simulation
Date: Thu, 05 Sep 2002 13:21:25 -0600
From: dkomo <dkomo...@cris.com>
Newsgroups: talk.orig
I ran across an interesting thought experiment that illustrates how
neutral genes in a small population can change frequencies due solely
to sampling error/genetic drift. In other words, the population can
evolve even in the absence of any selection pressure.
Consider a jar full of 45 red marbles and 55 blue marbles. These
represent the blue and red alleles of a neutral gene. To simulate the
fact that only a certain fraction of our marble "organisms" will be
able to reproduce (the rest will die or be unable to reproduce because
of lack of food or water, disease, etc.) select 50 marbles at random
and throw them away. The remaining marbles in the jar are allowed to
reproduce by creating a copy of their allele, returning the size of
the population back to 100 marbles.
For example, let's say that in the 50 marbles selected, 20 were red
and 30 were blue. The remaining 25 red marbles in the jar reproduce
and so do the remaining 25 blue marbles. The jar now contains 50 red
marbles and 50 blue marbles.
Repeat this experiment 100 times. At the end of the trials, which of
these is correct:
1. The jar will contain 100 red marbles.
2. The jar will contain 100 blue marbles.
3. The jar will contain a mix of red and blue marbles in
approximately the same ratio as it had initially.
4. It's not possible to predict the marble ratios.
5. None of the above.
6. I don't know.
7. Who cares?
Note that if the number of either the red or blue marbles reaches 100,
no further change is possible because "mutations" are disallowed
(red->blue, or blue->red during reproduction).
I'll post the answer a little latter.
Larry Moran
> dkomo wrote:
[snip]
>> We have plenty of "just so" stories to explain each and every
>> purported adaptation. Any amateur evolution theorist can come up with
>> half a dozen armchair explanations for each such trait. What we don't
>> have in most cases is empirical proof that a particular feature of an
>> organisn is indeed an adaptation to the environment.
>>
> Yes, so we need empirical observation to resolve this argument. My
> point is that we know that spatial and temporal variation in selection
> pressures occurs, so we can't rule them out just because we don't like
> them.
Right. We also know for a fact that random genetic drift occurs so
you can't rule it out just because you don't like it.
> Examining their effects is difficult (I've looked at both. One
> study needed a 60 year time seies, the other merely a crossing
> experiment with a couple of thousand frogs).
Nobody said it was easy to prove natural selection or random genetic drift.
The key point to keep in mind is that in the absence of proof for one
mechanism or another you have to keep an open mind and not just assume
that it's your favorite mechanism that works.
It's easy to make up "just-so" adaptionist stories. The tricky part is
realizing that they are just stories and not real explanations.
>>>Of course, drift may also be an explanation, but I believe that we can
>>>only separate out the contributions of the different causes empirically.
>>
>> It may be that many features of organisms are incidental and play no
>> role in their evolution. That doesn't necessarily imply that these
>> features are subject to drift.
If the features are not adaptive then they must be neutral (or nearly
neutral). If the aleles for these features are neutral with respect to
fitness than there frequency in the population *will* be subject to
random genetic drift. You can't stop it.
>> Drift is a phenomenon of small, isolated populations.
This is an incorrect statement.
> And there are a lot of them about, even in organisms like insects.
Exactly right. In the real world it's almost impossible to have a large
population of randomly mating individuals (i.e., panmitic). Almost any
population that you can think of is subdivided into a large number of
much smaller sub-populations that are more-or-less genetically isolated
from each other. This is obvious in humans but it's true of every other
species as well.
Larry Moran
j...@removethispart.gs.washington.edu
Tim Tyler <t...@tt1lock.org> wrote:
>Another quotable bit:
>
>``Darwinian selection remains the only explanation for adaptive
> evolution - and it is arguable (I would argue) that most if not
> all the evolutionary changes we actually see in the macroscopic
> world (as opposed to those concealed among the molecules) are
> adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
>
>I'm not sure about the "all" but I'm inclined to agree with the "most".
>
>Drift may have something to say about small populations on islands
>around speciation events - but it's probably a bit player in most
>other places - as far as the *features* of organisms go (as opposed
>to the makeup of their genes).
Actually Dawkins's quote seems not to mention Kimura. And Kimura did not
argue that visible morphological characters "in the macroscopic world"
were to be explained by neutral mutation. His argument was about the bulk
of change at the molecular level (which Dawkins calls changes "concealed
among the molecules"). He would have agreed that most of the visible
morphological characters had their adaptive change explained by natural
selection. Kimura also allowed for many mutants being eliminated owing to
being deleterious.
So this thread is not discussing anything to do with Kimura.
--
Joe Felsenstein j...@removethispart.gs.washington.edu
Department of Genome Sciences and Department of Biology,
University of Washington, Box 357730, Seattle, WA 98195-7730 USA
Larry Moran
> Larry Moran wrote:
>> On Tue, 24 Feb 2004 20:57:28 +0000 (UTC), Anon.
>> <bob....@SOD.OFF.Spammers.helsinki.fi> wrote:
>>>dkomo wrote:
>>>>Tim Tyler wrote:
[snip]
>>>Of course, drift may also be an explanation, but I believe that we can
>>>only separate out the contributions of the different causes empirically.
>>
>> Yes. Until we can actually test the hypotheses it's wise not to *assume*
>> that all morphological features are adaptations, don't you think?
>>
> As long as we can't exclude non-adaptive explanations, then we can't
> dismiss them. But there may be occasions when making that assumption
> does lead to further enlightenment. It seems to be a problem of
> scientific rhetoric.
>
> Hmm. I'm not sure whether I answered you or not.
Yes, you've helped me to understand your point of view. :-)
>> Tim seems to be making the default assumption that most morphological
>> features are due to natural selection. Dawkins certainly makes that
>> assumption. Is this valid?
>>
> Well, it's valid. Is it correct? My feeling is that it is, but if
> someone show me evidence that it isn't, then I'll change my mind.
I can understand your "feeling." Since we don't have very good evidence
one way of the other is it valid science to rely on "feeling"? Why are
you asking for experimental evidence against your feeling? I could just
as easily state that most features are due to drift and it's up to you
to prove otherwise. Would that be an example of good science?
Why don't we just say that morphological features can become fixed in
a population by adaptation - and quote some known expamples. We don't
know if *most* morphological features are due to adaptation or whether
they are accidents of evolution.
Larry Moran
Tim Tyler
> Tim Tyler <t...@tt1lock.org> wrote:
> >Another quotable bit:
> >
> >``Darwinian selection remains the only explanation for adaptive
> > evolution - and it is arguable (I would argue) that most if not
> > all the evolutionary changes we actually see in the macroscopic
> > world (as opposed to those concealed among the molecules) are
> > adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
[...]
> Actually Dawkins's quote seems not to mention Kimura. And Kimura did not
> argue that visible morphological characters "in the macroscopic world"
> were to be explained by neutral mutation. His argument was about the bulk
> of change at the molecular level (which Dawkins calls changes "concealed
> among the molecules"). He would have agreed that most of the visible
> morphological characters had their adaptive change explained by natural
> selection. Kimura also allowed for many mutants being eliminated owing to
> being deleterious.
>
> So this thread is not discussing anything to do with Kimura.
To explain/justify my subject line, I'll add a little bit to the quote -
fair use permitting ;-):
``The only point of controversy introduced by Kimura is how many
mutations are neutral. Kimura thought it was the great majority
which, if true, is very nice for the molecular clock.
Darwinian selection remains the only explanation for adaptive
evolution - and it is arguable (I would argue) that most if not
all the evolutionary changes we actually see in the macroscopic
world (as opposed to those concealed among the molecules) are
adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
Tim Tyler
> Tim Tyler <t...@tt1lock.org> wrote in message news:<c1k47m$8hu$1...@darwin.ediacara.org>...
> > dkomo <dkomo...@cris.com> wrote or quoted:
> > > I was under the impression that panadaptationism is frowned upon
> > > these days by most evolutionists.
> >
> > Adaptations are certainly all over the place.
> >
> > "Panadaptationism" is - or ought to mean "adaptations everywhere" -
> > but exactly how common that is supposed to mean isn't clear.
>
> seems to mean what you indicated it ought to mean, adaptations
> everywhere.
In which case the term is next to useless - nobody believes that:
``No Darwinian from Darwin on has expected that every possible feature
would be adaptive, and so panadaptationism is a strawman''
- http://www.users.bigpond.com/thewilkins/papers/Neplusultra.html
> Every trait is the result of adaptation (or at least
> primarily/dominantly the result of adaptation). Seems to be an
> endpoint on a spectrum. I can't imagine anyone is an acutal
> panadaptationist, but dawkin's certainly can safely be refered to as
> one.
``Most if not all of the evolutionary changes we see in the macroscopic
world [...] are adaptive and Darwinian.'' - p.85.
- "The Devil's Chaplain".
It seem's like he's avoided being a panadaptationist here -
since his wording avoids going for the "all" option.
Close - but no cigar, I reckon.
> > The word doesn't seem to be in the dictionary - has anyone actually
> > bothered to define it - or is it just a term of derision?
>
> probably in as much as 'big bang' was intended to be insulting.
Wasn't the term coined by Lewontin and Gould, though? I don't believe
a compliment was intended.
Anon.
> On Thu, 26 Feb 2004 16:44:30 +0000 (UTC),
> Anon. <bob....@SOD.OFF.Spammers.helsinki.fi> wrote:
>
>>>Tim seems to be making the default assumption that most morphological
>>>features are due to natural selection. Dawkins certainly makes that
>>>assumption. Is this valid?
>>>
>>
>>Well, it's valid. Is it correct? My feeling is that it is, but if
>>someone show me evidence that it isn't, then I'll change my mind.
>
>
> I can understand your "feeling." Since we don't have very good evidence
> one way of the other is it valid science to rely on "feeling"? Why are
> you asking for experimental evidence against your feeling? I could just
> as easily state that most features are due to drift and it's up to you
> to prove otherwise. Would that be an example of good science?
>
> Why don't we just say that morphological features can become fixed in
> a population by adaptation - and quote some known expamples. We don't
> know if *most* morphological features are due to adaptation or whether
> they are accidents of evolution.
>
have become fixed, because most traits have a function. If you're
saying that they became fixed by drift, then you're invoking a rather
strange form of the blind watchmaker.
William Morse
news:c1ikj8$2pkb$1...@darwin.ediacara.org:
Haven't we had this debate before on sbe? I believe it was termed at
that time the "null hypothesis" rather than the "default assumption". My
personal opinion, FWIW, is that we can make a good first guess about a
trait without the need for a default.
If the trait shows little
variation throughout a large population or is strongly correlated with
an obvious environmental variable, and has an obvious relation to an
aspect of species behavior, one can make the default assumption that it
is an adaptation, especially if it has existed for a long period.(Again
based on recollection, Wirt did a much better job than I just did of
defining what traits could be considered adaptive as a default).
Examples would include large ears in elephants, skin color in humans, and
almost any morphological feature of horseshoe crabs.
If the trait shows
wide variation throughout a population regardless of environmental
variables, or is confined to isolated subpopulations with no obvious
relation to fitness, one can make the default assumption that it is due
to drift. Examples include coat color in domestic cats and the Rh- blood
type in humans.
Note that I am cheating somewhat, as I am assuming there is at least
some data available to make a "default" assumption. Also, the above
_are_ only default assumptions - either may be proved false by better
data, so ultimately I agree with Bob. Also note that there will be a
lot of traits - morphological features and otherwise - that will not
fall into either category. In this case the
adaptationists (including myself) will dream up unsubstantiated Just So
stories to which the drifters (sorry -
the term has both a nice slightly pejorative ring to my ears as well as
reminding me of the 60's rock band) will recoil in horror :-)
Yours,
Bill Morse
Tim Tyler
> I can understand your "feeling." Since we don't have very good evidence
> one way of the other is it valid science to rely on "feeling"? Why are
> you asking for experimental evidence against your feeling? I could just
> as easily state that most features are due to drift and it's up to you
> to prove otherwise. Would that be an example of good science?
>
> Why don't we just say that morphological features can become fixed in
> a population by adaptation - and quote some known expamples. We don't
> know if *most* morphological features are due to adaptation or whether
> they are accidents of evolution.
Simon Conway Morris's latest book bears on this question:
``Life's Solution : Inevitable Humans in a Lonely Universe''
It suggests that evolution has designed functionally the *same* structure
from *different* starting points - in a very large number of cases.
He gives quite a few good examples of this convergent evolution.
It is easily explicable on the assumption that "most features" of
organisms were adaptations - but would be puzzling if they were accidents.
Michael Ragland
What role do neutral mutations play in evolution? One reads about
genetic drift and how much the immense genetic variety is due to neutral
mutations and inconsequential to survival and reproduction. Afterall, a
neutral mutation is a mutation which results in a change of the genotype
without changing the phenotype or associated fitness value. Or this this
too simplistic a definition of neutral mutation?
The role of neutral mutations are stressed in the theory of punctuated
equilibrium. As Gould maintained this theory was never intended to
replace Darwinian gradualism but rather to add to it. According to the
theory if enough "beneficial neutral mutations e.g. a combination which
is beneficial and reaches a certain theshold..it can result in an
episode of punctuated eqilibrium or speciation. Such an event doesn't
represent a major transition from one organism to another but rather
"little jumps".
My question is if enough neutral mutations accumulated which resulted in
some beneficial combination...wouldn't natural selection then act? What
determines that a particular accumulation of neutral mutations is
beneficial?
Michael Ragland
Guy Hoelzer
nygdan_mo...@yahoo.com wrote on 2/27/04 8:40 AM:
I am saying something roughly like your last alternative. I think that the
evidence is now overwhelming, and mostly overlooked by evolutionary
biologists, that natural selection is a particular form of more general
(thermodynamic) set of optimizing, adaptive processes. Biology specializes
on natural selection as an adaptive process, but there is no reason that
others kinds of adaptive mechanisms can't also participate in causing
adaptive evolution.
Guy
Tim Tyler
> If the trait shows little
> variation throughout a large population or is strongly correlated with
> an obvious environmental variable, and has an obvious relation to an
> aspect of species behavior, one can make the default assumption that it
> is an adaptation, especially if it has existed for a long period.(Again
> based on recollection, Wirt did a much better job than I just did of
> defining what traits could be considered adaptive as a default).
> Examples would include large ears in elephants, skin color in humans, and
> almost any morphological feature of horseshoe crabs.
>
> If the trait shows wide variation throughout a population regardless of
> environmental variables, or is confined to isolated subpopulations with
> no obvious relation to fitness, one can make the default assumption
> that it is due to drift. Examples include coat color in domestic cats
> and the Rh- blood type in humans.
Genes for traits can reach fixation by accident in small populations.
They can remain fixed due to selective lock-in if other adaptations
come to depend on their presence.
Old, non-variable traits (of any sort) need not /necessarily/ represent
adaptations.
Incidentally, are you /really/ suggesting a human blood type is neutral?
Are not blood types often critical in disease resistance? That is surely
a case of parasite-driven selection favouring diversity.
Larry Moran
William Morse <wdm...@twcny.rr.com> wrote:
> lam...@bioinfo.med.utoronto.ca (Larry Moran) wrote in
> news:c1ikj8$2pkb$1...@darwin.ediacara.org:
[snip]
>> Tim seems to be making the default assumption that most
>> morphological features are due to natural selection. Dawkins
>> certainly makes that assumption. Is this valid?
>
> Haven't we had this debate before on sbe? I believe it was termed
> at that time the "null hypothesis" rather than the "default
> assumption". My personal opinion, FWIW, is that we can make a good
> first guess about a trait without the need for a default.
Yes, I think we've debated this before on sbe. :-)
Is there a rule about not bringing up the same topic again? It
seems to me that there are a some topics that seem to be "debated"
over and over again on this newsgroup so I assumed that this was
okay. :-)
Seriously, I think it's more interesting to discuss adaptionism and
random genetic drift than some of the other things that are taking
up time on sbe. Do you agree?
> If the trait shows little
> variation throughout a large population or is strongly correlated with
> an obvious environmental variable, and has an obvious relation to an
> aspect of species behavior, one can make the default assumption that it
> is an adaptation, especially if it has existed for a long period.(Again
> based on recollection, Wirt did a much better job than I just did of
> defining what traits could be considered adaptive as a default).
> Examples would include large ears in elephants, skin color in humans, and
> almost any morphological feature of horseshoe crabs.
>
> If the trait shows
> wide variation throughout a population regardless of environmental
> variables, or is confined to isolated subpopulations with no obvious
> relation to fitness, one can make the default assumption that it is due
> to drift. Examples include coat color in domestic cats and the Rh- blood
> type in humans.
Hmmmm .... I would have thought that ear size in elephants and skin
color in humans were excellent example of drift. Don't you see how
difficult it is to make general rules? Your decision about what the
"default" hypothesis should be depends to a great extent on your
original biases. This is exactly the point that Lewontin and Gould
made in their original paper. If you tend to emphasize natural
selection in your thinking about evolution then you will look to
adaptive explanations ahead of non-adaptive explanations.
> Note that I am cheating somewhat, as I am assuming there is at
> least some data available to make a "default" assumption.
Part of the problem is that even the selection of "data" has
built-in biases. If you are an adaptionist, and you prefer an
adaptionist explanation, then you go looking for data to support
your assumption. For example, if you think human skin color is
adaptive then the only "data" you quote is the little bit that
might explains why people with white skin lived in Northern Europe.
> Also, the above _are_ only default assumptions - either may be
> proved false by better data, so ultimately I agree with Bob.
> Also note that there will be a lot of traits - morphological
> features and otherwise - that will not fall into either category.
> In this case the adaptationists (including myself) will dream up
> unsubstantiated Just So stories to which the drifters (sorry -
> the term has both a nice slightly pejorative ring to my ears as
> well as reminding me of the 60's rock band) will recoil in
> horror :-)
No offense. I'm a drifter in the sense that it's part of my
self-proclaimed "mission" to educate people about the importance
of random genetic drift and evolution by accident. I'm not having
much luck on sci.bio.evolution. This newsgroup is heavily dominated
by people who reject the very concept of drift or who have deliberately
chosen not to understand it. I find this very strange in a newsgroup
that's supposed to be devoted to discussing evolution at a serious
level.
Larry Moran
Jeffrey Turner
> Jeffrey Turner wrote:
>>Tim Tyler wrote:
>>
>>
>>>Drift is most effective when population sizes are small. Selection
>>>is most effective when population sizes are large. I reckon this fact
>>>(in conjunction with nature's population sizes) will often limit's drift's
>>>usefulness as an explanation for features of organisms.
>>
>>What is "drift"? Genes mutate randomly, malign mutations die out,
>>mutations that have no effect on an organism don't really matter and
>>beneficial mutations propagate and supplant organisms without that
>>mutation. This generally leads to a new species, in time. But what's
>>"drift"?
>
>
Off-hand, I'd say 3 is probably correct. There is a finite
probability of any other distribution, however. Is one hundred
individuals a realistic population? It seems very small, and the odds
of any appreciable "drift" decrease dramatically as population size
increases. So, it seems to me, drift may be conceptualizable but it
won't be a significant phenomenon. As for how any significant
"deviant" population would arise in the first place without selection,
it must either have arisen by mutation or been inherited early in the
history of a species _or_ occurred as a fairly regular mutation in a
well established species.
From an evolutionary standpoint, the most realistic answer is 7.
--Jeff
--
A man, a plan, a cat, a canal - Panama!
Ho, ho, ho, hee, hee, hee
and a couple of ha, ha, has;
That's how we pass the day away,
in the merry old land of Oz.
TomHendricks474
from *different* starting points - in a very large number of cases.
He gives quite a few good examples of this convergent evolution.
It is easily explicable on the assumption that "most features" of
organisms were adaptations - but would be puzzling if they were accidents.
-- >>
If you consider life as the ability to moderate heat then life everywhere would
be convergent in that respect.
If they had variants that were neutral to heat moderation then they would lead
in different directions.
R.Schenck
besides nat select. ? I understand that other mechanims are involved
in evolution, but not that they necessarily lead to adapatations,
whereas natural selection 'selects' for adapatations. So what are
these other mechanisms that select adapations? I guess i don't expect
a full explanation here, but what texts go into it at least? I
probably shouldn't be asking for -more- stuff to read now, but at
least i could add it to the list.
Tim Tyler
> > Guy Hoelzer <hoe...@unr.edu> wrote in message
> >> My point was that natural selection is not the only possible adaptive
> >> process.
> >
> > what other adpative process is there? i understand that drift is
> > useful for 'adaptive peaks and valleys' and all, but even then its
> > selection that is the over-riding factor. Or are you saying that
> > selection is merely not the only mechanism/force/player whatever
> > involved?
>
> I am saying something roughly like your last alternative. I think that the
> evidence is now overwhelming, and mostly overlooked by evolutionary
> biologists, that natural selection is a particular form of more general
> (thermodynamic) set of optimizing, adaptive processes.
I.e. self-organising systems.
> Biology specializes on natural selection as an adaptive process, but
> there is no reason that others kinds of adaptive mechanisms can't also
> participate in causing adaptive evolution.
I'm sure they do.
To take a simple example, I think the human brain is /heavily/ influenced
by "self-organising" mechanisms during its development.
Speaking /very/ crudely, I think the genome says something like: make lots
of these neuron things, according to these rules, wire them together with
these sensors and these motor units - and then let them get on with things.
The resulting adult brain thus owes a great deal to self-organising
processes.
Such processes can influence gene frequencies via selection and the
Baldwin effect.
Having said that, natural selection is /still/ pretty fundamental.
Since it gets to decide which self-organising systems exist and
which don't, it pretty-much has the final word.
In the future we will see completely new ways for adaptions to
arise in organisms - namely they will be designed and engineered
to be there - the products of "mutations" directed by intelligent
design - but even then, natural selection will still preside over
everything.
dkomo
>
> Note that I am cheating somewhat, as I am assuming there is at least
> some data available to make a "default" assumption. Also, the above
> _are_ only default assumptions - either may be proved false by better
> data, so ultimately I agree with Bob. Also note that there will be a
> lot of traits - morphological features and otherwise - that will not
> fall into either category. In this case the
> adaptationists (including myself) will dream up unsubstantiated Just So
> stories to which the drifters (sorry -
> the term has both a nice slightly pejorative ring to my ears as well as
> reminding me of the 60's rock band) will recoil in horror :-)
>
Right. As far as I can tell, Gould's spandrels don't fall into either
category. These are incidental traits produced as side-effects of the
overall morphology of an organism. Spandrels are not adaptations nor
do they result from genetic drift.
John Edser
Larry Moran <lam...@bioinfo.med.utoronto.ca> wrote or quoted:
> I can understand your "feeling." Since we don't have very good evidence
> one way of the other is it valid science to rely on "feeling"? Why are
> you asking for experimental evidence against your feeling? I could just
> as easily state that most features are due to drift and it's up to you
> to prove otherwise. Would that be an example of good science?
>
> Why don't we just say that morphological features can become fixed in
> a population by adaptation - and quote some known expamples. We don't
> know if *most* morphological features are due to adaptation or whether
> they are accidents of evolution.
TT:-
Simon Conway Morris's latest book bears on this question:
``Life's Solution : Inevitable Humans in a Lonely Universe''
It suggests that evolution has designed functionally the *same* structure
from *different* starting points - in a very large number of cases.
He gives quite a few good examples of this convergent evolution.
It is easily explicable on the assumption that "most features" of
organisms were adaptations - but would be puzzling if they were accidents.
JE:-
Why is it impossible for gene centric Neo Darwinists to
understand that the probable _rate_ of "accidents" such
as sampling error (genetic drift) can be selected at the
Darwinian fertile organism level of selection?
Respectfully,
John Edser
Independent Researcher
PO Box 266
Church Pt
NSW 2105
Australia
dkomo
The answer is (5) and is given in the thread in which the original
post appeared:
To summarize what appeared there, I wrote:
"The answer is (5) above. (1) and (2) are each possible, with
probabilities 0.198 and 0.287, as Chris Ho Stuart pointed out. There
is also a small chance of (3). (4) is clearly incorrect because it
*is* possible to make a statistical prediction of the distribution of
marbles after 100 experiments.
There was a variety of interesting responses in this thread. The main
thing I wanted to point out with this example is that a statistical
process can drive an allele distribution in a population either to
fixation, where the frequency of the allele becomes 100%, or to
extinction, where it disappears from the population. And such a
process is independent of any selection pressure -- that is, the
selection coefficient of the allele is near zero.
In particular, if the jar starts out with 50 red and 50 blue marbles,
it will *inevitably* end up with either 100 red marbles or 100 blue
after a sufficiently large number of "generations." This can be
proven mathematically. The probability of either case is 0.50. I
found this to be a fascinating counterintuitive result. The intuitive
situation would be a aimless drifting around the equilibrium point of
50 red and 50 blue.
The other interesting result is what happens to a *single* mutation,
e.g. a single red marble in a population of 99 blue marbles. It has
only a 1% chance of reaching fixation and a 99% chance of being
eliminated. Thus, only 1 out of every 100 neutral mutations can
stabilize within the population."
Mark VandeWettering computed the results using monte carlo
simulation. Chris Ho Stuart computed it analytically, but the
calculation was so laborious he needed to write a computer program to
derive the final probabilities. His 2nd post in the thread contains
the C code for his program.
> Is one hundred individuals a realistic population?
According to what people have stated here on sbe, subpopulations this
small or smaller are the *norm* for genetics.
> It seems very small, and the odds
> of any appreciable "drift" decrease dramatically as population size
> increases.
Yes, and I'd like to know exactly how fast it decreases as population
size increases. I may write my own monte carlo simulation. The
discussion of drift on sbe has thus far been too qualitative and
vague.
> So, it seems to me, drift may be conceptualizable but it
> won't be a significant phenomenon.
Not if small subpopulations are the dominant reality in population
genetics.
> As for how any significant
> "deviant" population would arise in the first place without selection,
> it must either have arisen by mutation or been inherited early in the
> history of a species _or_ occurred as a fairly regular mutation in a
> well established species.
>
> From an evolutionary standpoint, the most realistic answer is 7.
>
That's what the debate here is all about.
Tim Tyler
>> > Why don't we just say that morphological features can become fixed in
>> > a population by adaptation - and quote some known expamples. We don't
>> > know if *most* morphological features are due to adaptation or whether
>> > they are accidents of evolution.
>>
>> Simon Conway Morris's latest book bears on this question:
>>
>> ``Life's Solution : Inevitable Humans in a Lonely Universe''
>>
>> It suggests that evolution has designed functionally the *same* structure
>> from *different* starting points - in a very large number of cases.
>>
>> He gives quite a few good examples of this convergent evolution.
>>
>> It is easily explicable on the assumption that "most features" of
>> organisms were adaptations - but would be puzzling if they were accidents.
>
> Why is it impossible for gene centric Neo Darwinists to
> understand that the probable _rate_ of "accidents" such
> as sampling error (genetic drift) can be selected at the
> Darwinian fertile organism level of selection?
Organisms can alter their mutation rate by the degree of investment
they put into insulation, gene repair, cell house-keeping - and so
on. Normally they try to make mutation levels low - but can't
necessarily afford the budget to do it really effectively.
...but what does that have to do with the issue?
Surely there is no argument that the supposed examples of genetic
drift are /really/ adaptations - because organisms have some
control over their own mutation rates ;-)
I do think homoplasy is significant.
It may not allow us to say much about the relative significance
of adaptation and drift - but it does mean that we can point to
some specific organism features and say - with a reasonable level
of confidence - this as an adaptation - and so is this - and so
is this - without being accused of concocting "just so" stories.
Morris's purpose is not illumating this debate - but some of the
most striking illustrations of homoplasy I've seen are to be found
in his book.
Tim Tyler
> > dkomo wrote:
> > > Jeffrey Turner wrote:
> > >>Tim Tyler wrote:
> > >>>Drift is most effective when population sizes are small. Selection
> > >>>is most effective when population sizes are large. I reckon this
> > >>>fact (in conjunction with nature's population sizes) will often
> > >>>limit's drift's usefulness as an explanation for features of
> > >>>organisms.
[...]
> > > 1. The jar will contain 100 red marbles.
> > > 2. The jar will contain 100 blue marbles.
> > > 3. The jar will contain a mix of red and blue marbles in
> > > approximately the same ratio as it had initially.
> > > 4. It's not possible to predict the marble ratios.
> > > 5. None of the above.
> > > 6. I don't know.
> > > 7. Who cares?
> > >
> > > Note that if the number of either the red or blue marbles reaches 100,
> > > no further change is possible because "mutations" are disallowed
> > > (red->blue, or blue->red during reproduction).
> >
> > Off-hand, I'd say 3 is probably correct. There is a finite
> > probability of any other distribution, however.
>
> The answer is (5) and is given in the thread in which the original
> post appeared:
>
> http://tinyurl.com/2crm3
[...]
> The main thing I wanted to point out with this example is that a
> statistical process can drive an allele distribution in a population
> either to fixation, where the frequency of the allele becomes 100%, or
> to extinction, where it disappears from the population. And such a
> process is independent of any selection pressure -- that is, the
> selection coefficient of the allele is near zero.
I think you mean "*IF* the selection coefficient of the allele is near
zero" Large selection pressures are not irrelevant - and would
change the answer to the problem from 5 to 1 or 2.
> > Is one hundred individuals a realistic population?
>
> According to what people have stated here on sbe, subpopulations this
> small or smaller are the *norm* for genetics.
For the genetics of small populations on the verge of extiction?
The quantitly of relevance of the calculaton is known as the
"effective populaton size".
An effective population size of 500 is considered to be a threshold
for status as an endangered species.
The figures you are talking about (in isolated populations) would
represent effective population sizes of 25-50 - putting them straight
into the red, flashing region of the endangered species list.
It is true that we are in the middle of a mass extinction at the momement
- and so it's inevitable that more than the usual number of species are
going through small population sizes as part of the process of
shuffling off this mortal coil.
However, the population sizes you talk about still seem to be very low.
Guy Hoelzer
nygdan_mo...@yahoo.com wrote on 2/29/04 10:34 AM:
>> I am saying something roughly like your last alternative. I think that the
>> evidence is now overwhelming, and mostly overlooked by evolutionary
>> biologists, that natural selection is a particular form of more general
>> (thermodynamic) set of optimizing, adaptive processes. Biology specializes
>> on natural selection as an adaptive process, but there is no reason that
>> others kinds of adaptive mechanisms can't also participate in causing
>> adaptive evolution.
> i am curious about this, what other mechanisms lead to adaption
> besides nat select. ?
"Learning" is an example familiar to biologists. I think that "entrainment"
is a more general physical example.
> I understand that other mechanims are involved
> in evolution, but not that they necessarily lead to adapatations,
> whereas natural selection 'selects' for adapatations. So what are
> these other mechanisms that select adapations?
To keep the discussion centered on biological evolution, you should consider
the "Baldwin Effect", as suggested by Tim Tyler.
> I guess i don't expect
> a full explanation here, but what texts go into it at least? I
> probably shouldn't be asking for -more- stuff to read now, but at
> least i could add it to the list.
I don't think that any of the standard textbooks on evolutionary biology
deal with these issues. IMHO this is a problem. You might want to add
"Darwinism Evolving" (Depew and Weber) or "Signs of Life" (Sole and Goodwin)
to your list. Also, you will find tons of material on the Baldwin Effect
with a Google search.
Cheers,
Guy
dkomo
What I meant is that the statistical process alone can strongly affect
the allele frequencies and that can happen in the absence of any
selection pressure, which is when the selection coefficient of the
allele is effectively zero.
Even if there is selection pressure, the drift component still
operates independently. The final allele distribution will be a
result of the sum of both processes.
> > > Is one hundred individuals a realistic population?
> >
> > According to what people have stated here on sbe, subpopulations this
> > small or smaller are the *norm* for genetics.
>
> For the genetics of small populations on the verge of extiction?
>
> The quantitly of relevance of the calculaton is known as the
> "effective populaton size".
>
> An effective population size of 500 is considered to be a threshold
> for status as an endangered species.
>
> The figures you are talking about (in isolated populations) would
> represent effective population sizes of 25-50 - putting them straight
> into the red, flashing region of the endangered species list.
>
> It is true that we are in the middle of a mass extinction at the momement
> - and so it's inevitable that more than the usual number of species are
> going through small population sizes as part of the process of
> shuffling off this mortal coil.
>
> However, the population sizes you talk about still seem to be very low.
>
What I said about small populations had nothing to do with endangered
species. I was referring to the following statements here in this
thread:
dkomo:
It may be that many features of organisms are incidental and play no
role in their evolution. That doesn't necessarily imply that these
features are subject to drift. Drift is a phenomenon of small,
isolated populations.
Anon:
And there are a lot of them about, even in organisms like insects.
Larry Moran:
Exactly right. In the real world it's almost impossible to have a
large
population of randomly mating individuals (i.e., panmitic). Almost any
population that you can think of is subdivided into a large number of
much smaller sub-populations that are more-or-less genetically
isolated
from each other. This is obvious in humans but it's true of every
other
species as well.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
So if it is common to have genetically isolated small sub-populations
of large populations of animals, the phenomenon of genetic drift is
going to be dominant and very widespread. And that is going to blow a
huge hole into the side of theories that most features of organisms
are adaptations.
John Edser
> JE:-
> Why is it impossible for gene centric Neo Darwinists to
> understand that the probable _rate_ of "accidents" such
> as sampling error (genetic drift) can be selected at the
> Darwinian fertile organism level of selection?
TT:-
Organisms can alter their mutation rate by the degree of investment
they put into insulation, gene repair, cell house-keeping - and so
on. Normally they try to make mutation levels low - but can't
necessarily afford the budget to do it really effectively.
JE:-
My information is that loci mutation rates
are not consistent. The implication is
that nature has selected to reduce mutation
rates at _some_ loci but allow it to increase
at others, i.e. selection can favour more
or less variation at different loci so that
mutation _rates_ are under selective control.
TT:-
...but what does that have to do with the issue?
JE:-
As you may know I disallow drift as valid
"evolution" but allow it as "temporal
variation" because evolutionary theory
becomes non testable if random gene
freq. change is allowed as evolution
but remains testable when allowed as
temporal variation.
Just as selection can control the rate
of mutation at different loci and thus
control the rate of loci variation, nature
can control the rate of temporal variation.
Explaining drift as temporal variation
allows drift to be used as a
a powerful view for the adaptive argument
and not within just a non adaptive argument.
Drift is misused as just a competing force
_against_ Darwinian natural selection.
TT:-
Surely there is no argument that the supposed examples of genetic
drift are /really/ adaptations - because organisms have some
control over their own mutation rates ;-)
JE:-
I am arguing that "examples of genetic
drift are /really/ adaptations " in the
general but not the specific, sense, i.e.
nature cannot predict the outcome of
specific random events but she can increase
or decrease them where needed. Forms
that optimise variation can have a higher
fitness.
TT:-
I do think homoplasy is significant.
It may not allow us to say much about the relative significance
of adaptation and drift - but it does mean that we can point to
some specific organism features and say - with a reasonable level
of confidence - this as an adaptation - and so is this - and so
is this - without being accused of concocting "just so" stories.
JE:-
So called "just so" stories are IMO
maligned by the "drift is evolution"
school because "just so" stories have
been shown in the past to be valuable
and testable hypothesis. What remains
non testable is the common "drift is
evolution" concept.
Regards,
Jeffrey Turner
> William Morse <wdm...@twcny.rr.com> wrote:
>
>
>>If the trait shows little
>>variation throughout a large population or is strongly correlated with
>>an obvious environmental variable, and has an obvious relation to an
>>aspect of species behavior, one can make the default assumption that it
>>is an adaptation, especially if it has existed for a long period.(Again
>>based on recollection, Wirt did a much better job than I just did of
>>defining what traits could be considered adaptive as a default).
>>Examples would include large ears in elephants, skin color in humans, and
>>almost any morphological feature of horseshoe crabs.
>>
>>If the trait shows
>>wide variation throughout a population regardless of environmental
>>variables, or is confined to isolated subpopulations with no obvious
>>relation to fitness, one can make the default assumption that it is due
>>to drift. Examples include coat color in domestic cats and the Rh- blood
>>type in humans.
>
> Hmmmm .... I would have thought that ear size in elephants and skin
> color in humans were excellent example of drift.
So where are all the small-eared elephants?
> Don't you see how
> difficult it is to make general rules? Your decision about what the
> "default" hypothesis should be depends to a great extent on your
> original biases. This is exactly the point that Lewontin and Gould
> made in their original paper. If you tend to emphasize natural
> selection in your thinking about evolution then you will look to
> adaptive explanations ahead of non-adaptive explanations.
Considering genetic diversity, itself, gives a species an advantage,
you're going to have to explain why traits would develop for
non-adaptive reasons.
>>Note that I am cheating somewhat, as I am assuming there is at
>>least some data available to make a "default" assumption.
>
> Part of the problem is that even the selection of "data" has
> built-in biases. If you are an adaptionist, and you prefer an
> adaptionist explanation, then you go looking for data to support
> your assumption. For example, if you think human skin color is
> adaptive then the only "data" you quote is the little bit that
> might explains why people with white skin lived in Northern Europe.
>
>
>>Also, the above _are_ only default assumptions - either may be
>>proved false by better data, so ultimately I agree with Bob.
>>Also note that there will be a lot of traits - morphological
>>features and otherwise - that will not fall into either category.
>>In this case the adaptationists (including myself) will dream up
>>unsubstantiated Just So stories to which the drifters (sorry -
>>the term has both a nice slightly pejorative ring to my ears as
>>well as reminding me of the 60's rock band) will recoil in
>>horror :-)
>
>
> No offense. I'm a drifter in the sense that it's part of my
> self-proclaimed "mission" to educate people about the importance
> of random genetic drift
Genetic drift isn't very interesting, changes in phenotype are all
that evolution can work with.
> and evolution by accident.
Evolution by accident? Can you explain?
> I'm not having
> much luck on sci.bio.evolution. This newsgroup is heavily dominated
> by people who reject the very concept of drift or who have deliberately
> chosen not to understand it. I find this very strange in a newsgroup
> that's supposed to be devoted to discussing evolution at a serious
> level.
Maybe because "drift" doesn't seem to be very well defined.
Anon.
population.
Tim Tyler
> Evolution by accident? Can you explain?
Check out the differences between mammals and marsupials.
[what? Marsupials aren't mammals? - JAH]
To /some/ extent they exhibit convergent evolution - with similar forms
occupying similar niches.
However in other areas, they show significant differences.
Attributing these differences to selection caused by a different
environment is /possible/ - but mammals seem to do OK in Australia,
despite all the unusual and unfamiliar species over there - so the
environment probably isn't /that/ different.
The most obvious explanation of the differences is chance. Marsupials
*happened* to do things a different way - simply since there's more
than one way to do things - and the differences became fixed over time.
It /looks/ like the marsupials were better at *spreading* initailly -
but that they were not so good at defending their turf.
A similar thing - perhaps on an even more dramatic scale - happened in
South America 3 million years ago:
``In the upper Pliocene, 3 million years ago, the isthmus of Panama
reappeared as a result of changes in the earth's crust. This was a
disaster for many of the animals that had evolved in isolation in South
America. South America was invaded by deer, camels, raccoons, tapirs,
horses, mastodons, bears, peccaries, rabbits, shrews, cats, dogs,
weasels and rodents. For some reason these animals were able to
displace many of the South American species, driving many of them
to extinction.''
- http://darwin.bio.uci.edu/~sustain/bio65/lec02/b65lec02.htm#SouthAm
While divergence can be caused by drift, such large scale displacements
of whole species are examples of selection.
It /often/ seems to be the smaller population that suffers when
populations join.
Perhaps there are fewer different sorts of competitor in the smaller
environment - and so less pressure.
Or perhaps the smaller environment is likely to be less well furnished
with specialised species in the first place - so when existing
specialists do arrive they are simply better equipped than the natives
(who have more recently adopted the roles) to exploit the available niches.
Tim Tyler
> Tim Tyler wrote:
> > dkomo <dkomo...@cris.com> wrote or quoted:
> > For the genetics of small populations on the verge of extiction?
> >
> > The quantitly of relevance of the calculaton is known as the
> > "effective populaton size".
> >
> > An effective population size of 500 is considered to be a threshold
> > for status as an endangered species.
>
> What I said about small populations had nothing to do with endangered
> species. I was referring to the following statements here in this
> thread:
[...]
> Larry Moran:
>
> [...] In the real world it's almost impossible to have a large
> population of randomly mating individuals (i.e., panmitic). Almost any
> population that you can think of is subdivided into a large number of
> much smaller sub-populations that are more-or-less genetically
> isolated from each other. This is obvious in humans but it's true of
> every other species as well.
>
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> So if it is common to have genetically isolated small sub-populations
> of large populations of animals, the phenomenon of genetic drift is
> going to be dominant and very widespread. And that is going to blow a
> huge hole into the side of theories that most features of organisms
> are adaptations.
Humans are "subdivided into a large number of much smaller
sub-populations that are more-or-less genetically isolated
from each other"?
Give me a break. These populations are extremely unlikely to
/actually/ be genetically isolated from one another. The number of
migrants between groups needed to destroy the effect of drift is
notorious for being low - of the order of one migrant per generation -
and not many populations are *that* isolated.
Most of humanity is one big genetic melting pot. There are a /few/
areas where small populations have invaded other cultures and mate
mostly with their neighbours - and take things to the point of
inbreeding depression - but this isn't common and doesn't last long.
Humans deliberately avoid inbreeding - and are usually successful at
doing it.
Larry Moran
Jeffrey Turner <jtu...@localnet.com> wrote:
> Larry Moran wrote:
>> William Morse <wdm...@twcny.rr.com> wrote:
>>
>>>If the trait shows little variation throughout a large population or is
>>>strongly correlated with an obvious environmental variable, and has an obvious
>>>relation to an aspect of species behavior, one can make the default assumption
>>>that it is an adaptation, especially if it has existed for a long period.
>>>(Again based on recollection, Wirt did a much better job than I just did of
>>>defining what traits could be considered adaptive as a default). Examples
>>>would include large ears in elephants, skin color in humans, and almost any
>>>morphological feature of horseshoe crabs.
>>>
>>>If the trait shows wide variation throughout a population regardless of
>>>environmental variables, or is confined to isolated subpopulations with no
>>>obvious relation to fitness, one can make the default assumption that it is
>>>due to drift. Examples include coat color in domestic cats and the Rh- blood
>>>type in humans.
>>
>> Hmmmm .... I would have thought that ear size in elephants and skin
>> color in humans were excellent example of drift.
>
> So where are all the small-eared elephants?
Hmmmm ... I see where you're coming from. You observe that all modern species
of elphants have bigger ears than their ancestors and their modern cousins
such as manatees, dugongs, and hyraxes. This leads you to the conclusion that
large ears are an adaptation. However, if the ancestors of modern elephants
just happened to have large ears, and large ears were not a disadvantage,
then the presence of large ears could just as easily be due to drift. The
fact that modern species possess a certain characteristic feature is not
prima facie evidence of adaptation since drift and the founder effect would
achieve the same result.
But that's not what I had in mind. I was referring to the fact that Asian
elephants have much smaller ears than African elephants. If ear size is
under strong selection then one has to account for this fact. On the other
hand, if ear size is non-adaptive then the difference between Asian and
African elephants could be due entirely to chance.
>> Don't you see how
>> difficult it is to make general rules? Your decision about what the
>> "default" hypothesis should be depends to a great extent on your
>> original biases. This is exactly the point that Lewontin and Gould
>> made in their original paper. If you tend to emphasize natural
>> selection in your thinking about evolution then you will look to
>> adaptive explanations ahead of non-adaptive explanations.
>
> Considering genetic diversity, itself, gives a species an advantage,
> you're going to have to explain why traits would develop for
> non-adaptive reasons.
Two points ...
1. Genetic diversity cannot be an adaptation since this requires a form
of group selection that has been thoroughly discredited. If a species
accidently possesses more diversity then it will be the lucky survivor
when the environment changes. This is more like evolution by chance
that real adaptation.
2. All kinds of traits can arise by chance. Take the ability of some
people to roll their tongues as a simple example. Why do I have
to explain why traits would develop for non-adaptive reasons? Is
it because of your (irrational) belief that everything MUST be
an adaptation?
[snip]
>> No offense. I'm a drifter in the sense that it's part of my
>> self-proclaimed "mission" to educate people about the importance
>> of random genetic drift
>
> Genetic drift isn't very interesting, changes in phenotype are all
> that evolution can work with.
Two points ....
1. The mechanism of random genetic drift is the basic evolutionary
mechanism underlying most of molecular evolution. I find this very
interesting. You may not. Furthermore, I'm quite interested in
the organization of genomes and junk DNA. Part of the modern
explanation of genome evolution requries random genetic drift.
You may not be interested in this either. Finally, I'm really
interested in correct explanations of the main features of
modern species (and speciation in general). If you aren't interested
in random genetic drift then you mustn't be interested in those
things either. It's okay to focus all of your attention on
adaptations and to admit that nothing else about evolution interests
you. But please don't assume that others share your bias.
2. The most reasonable minimal definition of evolution is change in
the frequency of heritable characteristics in a population over
time. This definition includes fixation by random genetic drift of
almost neutral alleles. You seem to want to change that definition
to restrict it to changes in phenotype - where presumably you mean
only observable phenotypes. Furthermore, when you say that this is
"all that evolution can work" with you imply that evolution is
synonomous with natural selection. In other words, you would like to
change the definition of evolution so that the only "real" evolution
is adaptation. This is consistent with the fact that you aren't
interested in any other kind of evolution but here you go one step
farther. Now you are suggesting that we re-define evolution so
that my interests become illegitimate. If you succeed (highly
unlikely) then what word will you use for all those heritable changes
that aren't adaptations? Will this be pseudoevolution? :-)
>> and evolution by accident.
>
> Evolution by accident? Can you explain?
Yes, I'm referring to evolution that takes place without natural selection
playing a significnat role. It includes things such as the random
elimination of some species, and the survival of others, at the time of
mass extinctions. (The so-called "Field of Bullets" senario of David Raup.)
It includes lots of other things as well. When I use the phrase "evolution
by accident" I mean it to be a direct contrast to adaptionism. The phrase
is intended to provoke people into thinking outside their box. (It's
also a convenient way to emphasize the contrast between real evolution and
intelligent design.)
>> I'm not having
>> much luck on sci.bio.evolution. This newsgroup is heavily dominated
>> by people who reject the very concept of drift or who have deliberately
>> chosen not to understand it. I find this very strange in a newsgroup
>> that's supposed to be devoted to discussing evolution at a serious
>> level.
>
> Maybe because "drift" doesn't seem to be very well defined.
Not true. It's as well-defined as natural selection. It may be a more
difficult concept to grasp and it may be unfamiliar to those who have
been brought up on a steady diet of adaptionist dogma, but that's a
different kettle of fish. You can't dismiss random genetic drift just
because you don't understand it.
Larry Moran
Jeffrey Turner
True, but the advantage of large ears in a large mammal that can't
really stay out of the tropical sun is obvious. Why would you think
that big ears would be a random occurrence? Drift is probably a minor
effect, while founders are interesting because of the advantage that
made them a new species not because of their random minor traits.
> But that's not what I had in mind. I was referring to the fact that Asian
> elephants have much smaller ears than African elephants. If ear size is
> under strong selection then one has to account for this fact. On the other
> hand, if ear size is non-adaptive then the difference between Asian and
> African elephants could be due entirely to chance.
Gee, why don't humans have large ears if they are just by chance?
Ever think that climate differences account for the smaller ears in
Indian elephants? There's no reason to believe that non-adaptive
mutations lead to speciation - and that's where all the marbles are.
>>>Don't you see how
>>>difficult it is to make general rules? Your decision about what the
>>>"default" hypothesis should be depends to a great extent on your
>>>original biases. This is exactly the point that Lewontin and Gould
>>>made in their original paper. If you tend to emphasize natural
>>>selection in your thinking about evolution then you will look to
>>>adaptive explanations ahead of non-adaptive explanations.
>>
>>Considering genetic diversity, itself, gives a species an advantage,
>>you're going to have to explain why traits would develop for
>>non-adaptive reasons.
>
>
> Two points ...
>
> 1. Genetic diversity cannot be an adaptation since this requires a form
> of group selection that has been thoroughly discredited. If a species
> accidently possesses more diversity then it will be the lucky survivor
> when the environment changes. This is more like evolution by chance
> that real adaptation.
Discredited? We all know that in many species that have familial
groups, say lions, the males leave or are expelled from the group to
find mates elsewhere. That type of behavior occurs across many
species with the obvious effect of diversifying the genetics. I seem
to recall research that showed that pheromones may play a role in
selecting a mate with different characteristics even in humans.
> 2. All kinds of traits can arise by chance. Take the ability of some
> people to roll their tongues as a simple example. Why do I have
> to explain why traits would develop for non-adaptive reasons? Is
> it because of your (irrational) belief that everything MUST be
> an adaptation?
Not everything is an adaptation, but adaptation plays a much more
important role than chance.
> [snip]
>
>
>>>No offense. I'm a drifter in the sense that it's part of my
>>>self-proclaimed "mission" to educate people about the importance
>>>of random genetic drift
>>
>>Genetic drift isn't very interesting, changes in phenotype are all
>>that evolution can work with.
>
>
> Two points ....
>
> 1. The mechanism of random genetic drift is the basic evolutionary
> mechanism underlying most of molecular evolution. I find this very
> interesting. You may not. Furthermore, I'm quite interested in
> the organization of genomes and junk DNA. Part of the modern
> explanation of genome evolution requries random genetic drift.
> You may not be interested in this either. Finally, I'm really
> interested in correct explanations of the main features of
> modern species (and speciation in general). If you aren't interested
> in random genetic drift then you mustn't be interested in those
> things either. It's okay to focus all of your attention on
> adaptations and to admit that nothing else about evolution interests
> you. But please don't assume that others share your bias.
Adaptations ARE evolution. Evolution doesn't care about junk DNA or
mutations that are neutral from the perspective of natural selection.
> 2. The most reasonable minimal definition of evolution is change in
> the frequency of heritable characteristics in a population over
> time. This definition includes fixation by random genetic drift of
> almost neutral alleles. You seem to want to change that definition
> to restrict it to changes in phenotype - where presumably you mean
> only observable phenotypes. Furthermore, when you say that this is
> "all that evolution can work" with you imply that evolution is
> synonomous with natural selection. In other words, you would like to
> change the definition of evolution so that the only "real" evolution
> is adaptation. This is consistent with the fact that you aren't
> interested in any other kind of evolution but here you go one step
> farther. Now you are suggesting that we re-define evolution so
> that my interests become illegitimate. If you succeed (highly
> unlikely) then what word will you use for all those heritable changes
> that aren't adaptations? Will this be pseudoevolution? :-)
Your interests aren't "illegitimate," they are other aspects of
biology. But genetic drift isn't important to evolution, junk DNA and
other unexpressed genes aren't either. Biology and genetics are areas
that hold other intrinsic interest. Why are you trying to shoehorn
all of biology into the study of evolution?
>>>and evolution by accident.
>>
>>Evolution by accident? Can you explain?
>
> Yes, I'm referring to evolution that takes place without natural selection
> playing a significnat role. It includes things such as the random
> elimination of some species, and the survival of others, at the time of
> mass extinctions. (The so-called "Field of Bullets" senario of David Raup.)
Something usually causes mass extinctions. A significant stressor.
It may or may not be transitory. But I suspect that, for the most
part, we can find common characteristics among the surviving species
that would explain why they survived. I have my doubts that things
are totally random.
> It includes lots of other things as well. When I use the phrase "evolution
> by accident" I mean it to be a direct contrast to adaptionism. The phrase
> is intended to provoke people into thinking outside their box. (It's
> also a convenient way to emphasize the contrast between real evolution and
> intelligent design.)
Ah, curiosities for arguing with Luddites. Can you actually convince
them of anything?
>>>I'm not having
>>>much luck on sci.bio.evolution. This newsgroup is heavily dominated
>>>by people who reject the very concept of drift or who have deliberately
>>>chosen not to understand it. I find this very strange in a newsgroup
>>>that's supposed to be devoted to discussing evolution at a serious
>>>level.
>>
>>Maybe because "drift" doesn't seem to be very well defined.
>
> Not true. It's as well-defined as natural selection. It may be a more
> difficult concept to grasp and it may be unfamiliar to those who have
> been brought up on a steady diet of adaptionist dogma, but that's a
> different kettle of fish. You can't dismiss random genetic drift just
> because you don't understand it.
I can dismiss it because it's not significant in evolution. You
haven't shown any method by which it would cause speciation.
Tim Tyler
> 2. All kinds of traits can arise by chance. Take the ability of some
> people to roll their tongues as a simple example. [...]
Simple - but /not/ good - it seems:
I found an essay on whether this trait is genetic:
``Everybody who stayed awake through the first nine minutes of
high school biology knows the ability to roll your tongue
into the shape of a tube is hereditary.
"We know it's a dominant trait," Wayne Carley, executive
director of the National Association of Biology Teachers,
told me.
"We teach it because it's an easy thing to test: You either
can roll your tongue, or you can't." .
A public-affairs person at the National Center for Genome Research
confidently tells me the same thing. "If a child can, then
at least one of her parents can."
But she's wrong. All the biology teachers are wrong, too.
[...]
Back in 1952 "Matlock" (scientists, like detectives, go by
last name) concluded that identical twins don't always share
the tongue-rolling trait. In 1975 "Martin" demonstrated that
identical twins are no more likely to share tongue-rolling
than are fraternal twins. In 1983 a Hungarian named Forrai
found no genetic basis for tongue-curling -- or hand-
clasping or arm-folding. And studying the Greeks of
Thessaloniki in 1982, Cruz-Gonzalez established that while
dry ear wax and attached ear lobes are recessive traits,
which means you need the gene from both your parents, the
genetic basis for tongue-rolling was less clear. [...]''
- http://www.discovery.com/area/skinnyon/skinnyon970226/skinny1.html
I tracked down some of the references - and found:
``TONGUE CURLING, FOLDING, OR ROLLING''
- http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?cmd=entry&id=189300
...which draws much the same conclusion - and has a comprehensive
bibliography on the subject.
There is no good evidence that the trait is genetic - and much evidence
that it is not.
Tim Tyler
> 1. Genetic diversity cannot be an adaptation since this requires a form
> of group selection that has been thoroughly discredited. [...]
Hmm. What about sex? Hamilton and others have suggested that having
a different genotype from your neighbours offers some protection
from their parasites - and "having a different genotype from your
neighbours" is another way of saying "genetic diversity".
To me, sex looks like an adaptation where one of its major functions
is generating genetic diversity. The resulting diversity acts to
slow the spread of parasites through the population - and increases
the number of individuals who are not infected. This benefits the
population - but it /also/ benefits the individuals - and therefore does
not need much in the way of group selection to explain its existence.
Tim Tyler
> Jeffrey Turner <jtu...@localnet.com> wrote:
> > Larry Moran wrote:
> >> Hmmmm .... I would have thought that ear size in elephants and skin
> >> color in humans were excellent example of drift.
> >
> > So where are all the small-eared elephants?
>
> Hmmmm ... I see where you're coming from. You observe that all modern species
> of elphants have bigger ears than their ancestors and their modern cousins
> such as manatees, dugongs, and hyraxes. This leads you to the conclusion that
> large ears are an adaptation. [...]
A couple of "just so" stories - about why Asian elephants might not
/need/ such large ears:
Cooling off is a major challenge to a large creature such as an african
elephant. Their ears - and the skin behind them - are rich with
blood vessels - and the African elephant can fan its large ears backward
and forward to circulate cool air over these blood vessels and control its
body temperature.
``Sometimes they will even stand with their face to the wind and spread
their ears wide open to allow the wind to cool the blood in the arteries
of their ears.''
- http://ladybug.xs4all.nl/saint/pages/ele/
``Asian elephants are much smaller, weighing between 6,615 and 11,020
pounds at a height of about 7 to 12 feet compared to the 8,820 to
15,430 at 10 to 13 feet of the African elephant.''
- http://www.thewildones.org/Animals/elephant.html
A less extreme volume to surface area ratio will mean less need for
alternative thermoregulation strategies - since the bigger you are,
the harder it is to cool off.
Also, the Asian elephant lives further north than the African
one - so its typical environment may be cooler.
In the light of this, I doubt whether the resulting ear size is an
accidental feature.
Jeffrey Turner
> Jeffrey Turner <jtu...@localnet.com> wrote or quoted:
>
>
>>Evolution by accident? Can you explain?
>
> Check out the differences between mammals and marsupials.
>
> [what? Marsupials aren't mammals? - JAH]
>
> To /some/ extent they exhibit convergent evolution - with similar forms
> occupying similar niches.
>
> However in other areas, they show significant differences.
>
> Attributing these differences to selection caused by a different
> environment is /possible/ - but mammals seem to do OK in Australia,
> despite all the unusual and unfamiliar species over there - so the
> environment probably isn't /that/ different.
>
> The most obvious explanation of the differences is chance. Marsupials
> *happened* to do things a different way - simply since there's more
> than one way to do things - and the differences became fixed over time.
Sure. Species aren't perfect creations, just the best that could be
arranged for with the tools on hand.
> It /looks/ like the marsupials were better at *spreading* initailly -
> but that they were not so good at defending their turf.
Well, when you introduce a new species into an ecosystem it will
either be killed off or thrive and probably kill off or force out
other species. Oh, it could also find an empty niche and blend in.
> A similar thing - perhaps on an even more dramatic scale - happened in
> South America 3 million years ago:
>
> ``In the upper Pliocene, 3 million years ago, the isthmus of Panama
> reappeared as a result of changes in the earth's crust. This was a
> disaster for many of the animals that had evolved in isolation in South
> America. South America was invaded by deer, camels, raccoons, tapirs,
> horses, mastodons, bears, peccaries, rabbits, shrews, cats, dogs,
> weasels and rodents. For some reason these animals were able to
> displace many of the South American species, driving many of them
> to extinction.''
>
> - http://darwin.bio.uci.edu/~sustain/bio65/lec02/b65lec02.htm#SouthAm
>
> While divergence can be caused by drift, such large scale displacements
> of whole species are examples of selection.
>
> It /often/ seems to be the smaller population that suffers when
> populations join.
>
> Perhaps there are fewer different sorts of competitor in the smaller
> environment - and so less pressure.
>
> Or perhaps the smaller environment is likely to be less well furnished
> with specialised species in the first place - so when existing
> specialists do arrive they are simply better equipped than the natives
> (who have more recently adopted the roles) to exploit the available niches.
Hrm, changes in ecosystems happen - sometimes rapidly - due to
geological processes and species must either adapt or die out. That's
evolution. Evolution isn't always driven by advantageous mutations of
species within a stable ecosystem. You're not proposing any
significant change in the theory, just applying it to species in
extremis.
William Morse
news:c1tbc1$85n$1...@darwin.ediacara.org:
> William Morse <wdm...@twcny.rr.com> wrote or quoted:
>
>> If the trait shows little
>> variation throughout a large population or is strongly correlated
>> with an obvious environmental variable, and has an obvious relation
>> to an aspect of species behavior, one can make the default assumption
>> that it is an adaptation, especially if it has existed for a long
>> period.(Again based on recollection, Wirt did a much better job than
>> I just did of defining what traits could be considered adaptive as a
>> default). Examples would include large ears in elephants, skin color
>> in humans, and almost any morphological feature of horseshoe crabs.
>>
>> If the trait shows wide variation throughout a population regardless
>> of environmental variables, or is confined to isolated subpopulations
>> with no obvious relation to fitness, one can make the default
>> assumption that it is due to drift. Examples include coat color in
>> domestic cats and the Rh- blood type in humans.
>
> Genes for traits can reach fixation by accident in small populations.
Surely. This is why I left the caveat that the default assumption is only
an assumption - and why I did not include traits with little variation in
small populations.
> They can remain fixed due to selective lock-in if other adaptations
> come to depend on their presence.
In which case they will still show little variation in large populations
- but those populations will also give more opportunity for competing
suites of adaptations to develop and overcome the lock-in.
> Old, non-variable traits (of any sort) need not /necessarily/
> represent adaptations.
I disagree strongly. If they are not being fixed by stabilizing
selection, they will drift.
> Incidentally, are you /really/ suggesting a human blood type is
> neutral? Are not blood types often critical in disease resistance?
> That is surely a case of parasite-driven selection favouring
> diversity.
The Rh- example comes from Cavalli-Sforza. But yes he is really
suggesting that Rh- is due to drift.It apparently comes from a relatively
small (historically) population in central Europe - and given the extreme
effects on reproduction (you generally only get one child when mated with
an Rh+) it is unlikely to be parasite-driven. In fact he notes that the
absence of B blood types in Amerindians could also be due to drift -
although that one is open to question since it could also be parasite-
driven by syphilis.
Yours,
Bill Morse
William Morse
> On Sat, 28 Feb 2004 18:18:20 +0000 (UTC),
> William Morse <wdm...@twcny.rr.com> wrote:
>> lam...@bioinfo.med.utoronto.ca (Larry Moran) wrote in
>> news:c1ikj8$2pkb$1...@darwin.ediacara.org:
> Is there a rule about not bringing up the same topic again? It
> seems to me that there are a some topics that seem to be "debated"
> over and over again on this newsgroup so I assumed that this was
> okay. :-)
> Seriously, I think it's more interesting to discuss adaptionism and
> random genetic drift than some of the other things that are taking
> up time on sbe. Do you agree?
Yes, entirely. In fact I was hoping to encourage continued discussion
with my follow. You may think that drift is given short shrift on sbe,
but I think if you look at number of posters (vs. volume of posts by a
few individuals) you will find that most of us think drift is significant
in evolution - the interesting question is how significant, and this is
what I was trying to draw a bead on.
>> If the trait shows little
>> variation throughout a large population or is strongly correlated
>> with an obvious environmental variable, and has an obvious relation
>> to an aspect of species behavior, one can make the default assumption
>> that it is an adaptation, especially if it has existed for a long
>> period.(Again based on recollection, Wirt did a much better job than
>> I just did of defining what traits could be considered adaptive as a
>> default). Examples would include large ears in elephants, skin color
>> in humans, and almost any morphological feature of horseshoe crabs.
>>
>> If the trait shows
>> wide variation throughout a population regardless of environmental
>> variables, or is confined to isolated subpopulations with no obvious
>> relation to fitness, one can make the default assumption that it is
>> due to drift. Examples include coat color in domestic cats and the
>> Rh- blood type in humans.
>
> Hmmmm .... I would have thought that ear size in elephants and skin
> color in humans were excellent example of drift. Don't you see how
> difficult it is to make general rules? Your decision about what the
> "default" hypothesis should be depends to a great extent on your
> original biases. This is exactly the point that Lewontin and Gould
> made in their original paper. If you tend to emphasize natural
> selection in your thinking about evolution then you will look to
> adaptive explanations ahead of non-adaptive explanations.
I will stand by my example of ear size in elephants - my reference is a
book entitled "Why Elephants Have Big Ears" - which despite its title was
written by Chris Lavers, not Rudyard Kipling :-) In another follow on
this thread you questioned why Indian elephants have smaller ears. Lavers
notes that both Indian elephants and African forest elephants - both of
which have smaller ears than African savanna elephants - inhabit forests
with lower temperatures than the savanna. He also notes that woolly
mammoths had tiny ears.
Skin color in humans is obviously controversial, but is a very
interesting example. AFAIK skin pigmentation is fairly well correlated
with latitude in the Old World, even among populations with rather
different origins, e.g. Indo-Europeans in India and Bantu speakers in
central Africa. And there is a plausible explanation for this - the
balance between Vitamin D production and folate production. However there
is little variation with latitude in the New World - probably an example
of founder effect - while there is considerable variation among
relatively isolated island populations in New Guinea - probably an
example of sampling error.
>> Note that I am cheating somewhat, as I am assuming there is at
>> least some data available to make a "default" assumption.
>
> Part of the problem is that even the selection of "data" has
> built-in biases. If you are an adaptionist, and you prefer an
> adaptionist explanation, then you go looking for data to support
> your assumption.
Of course - that's how science works. Fortunately for me there are people
like you that prefer stochastic explanations and try to poke holes in my
data while finding data that support your assumptions. As long as we are
polite in our discourse, honest in our data, and don't exclude from the
table those with ideas out of the mainstream, the system works pretty
well.
> No offense. I'm a drifter in the sense that it's part of my
> self-proclaimed "mission" to educate people about the importance
> of random genetic drift and evolution by accident. I'm not having
> much luck on sci.bio.evolution. This newsgroup is heavily dominated
> by people who reject the very concept of drift or who have
> deliberately chosen not to understand it. I find this very strange in
> a newsgroup that's supposed to be devoted to discussing evolution at a
> serious level.
See my comment above. In fact, while I still (as you have undoubtedly
noted) have a strong adaptationist bias, I have learned a lot about drift
from discussions on this newsgroup, which have often lead me to do
further reading. You noted in another follow that you are interested in
the mechanism of speciation. While I can keep hoping, I have not seen any
convincing explanations based on adaptation for the extent and pace of
speciation. Adaptive explanations may explain _why_ there should be two
different niches available for sticklebacks in Canadian lakes, but not
_how_ one species could rapidly diversify to fill both niches. But it is
getting late, so perhaps I will leave further discussion of that topic
for another day.
Yours,
Bill Morse
dkomo
Natural selection does not and will not preside over everything. It
doesn't have any influence over those phenotypical features that are
neutral and don't affect the ability of an organism to reproduce.
Some of us believe that this constitutes the majority of features
observed, whether those features were produced by genetic drift or are
accidental side effects like spandrels, or are results of
self-organizing processes.
The new ways you're talking about also won't necessarily be affected
by natural selection either. Consider genetic engineering to boost
the intelligence of humans. Humans with IQ's of 250 are not
necessarily going to produce more children than those with IQ's of
95. In fact they may think that the intelligent thing is not to have
children at all. Natural selection can only act where there is
differential success in producing offspring. Yet here we can have a
case where there can be a constant, or perhaps even increasing number
of IQ 250 humans independent of the reproductive success of those
humans. How? By genetic engineering of the sperm or eggs of those
ordinary IQ humans who wish to have enhanced children.
What do you call someone who sees natural selection and adaptation
behind every rock? An Ultra-Darwinist.
Anon.
> On Tue, 2 Mar 2004 04:48:40 +0000 (UTC),
> Jeffrey Turner <jtu...@localnet.com> wrote:
>
>
> But that's not what I had in mind. I was referring to the fact that Asian
> elephants have much smaller ears than African elephants. If ear size is
> under strong selection then one has to account for this fact. On the other
> hand, if ear size is non-adaptive then the difference between Asian and
> African elephants could be due entirely to chance.
>
with different selection pressures, so they may have different optimum
ear sizes.
Pan-adaptionist? Me?
I think the explanation for large ears is that they are used for
cooling, in which case one could examine the effect of size on cooling,
and the necessity for cooling in the two environments, and see if the
elephants in India need less cooling. Then if you can show that there
is selection pressure against large ears (e.g. because they are
expensive to make, or they fray very easily), you might have an
explanation that would convince Larry. Without this sort of work, both
points of view can be supported, and indeed both should be supported,
until we have enough evidence to decide one way or the other.
>
>>>Don't you see how
>>>difficult it is to make general rules? Your decision about what the
>>>"default" hypothesis should be depends to a great extent on your
>>>original biases. This is exactly the point that Lewontin and Gould
>>>made in their original paper. If you tend to emphasize natural
>>>selection in your thinking about evolution then you will look to
>>>adaptive explanations ahead of non-adaptive explanations.
>>
>>Considering genetic diversity, itself, gives a species an advantage,
>>you're going to have to explain why traits would develop for
>>non-adaptive reasons.
>
>
> Two points ...
>
> 1. Genetic diversity cannot be an adaptation since this requires a form
> of group selection that has been thoroughly discredited. If a species
> accidently possesses more diversity then it will be the lucky survivor
> when the environment changes. This is more like evolution by chance
> that real adaptation.
>
Two points ...
1. Inbreeding depression is a form of lack of genetic diversity that can
increase the chance that a population goe extinct. This will generally
work at low effective population sizes.
2. If you view diversity as a trait of a group, and has sufficiently
high "heritability" (i.e. heritability at the group level), then it can
evolve. For example, if the environment keeps on changing. To be
honest, I doubt this is a major force in evolution, but it might work in
some cases, for example with species competing against each other. This
is an example of the sort of group selection that hasn't been
discredited (yet) - trait group selection.
Larry Moran
> Larry Moran wrote:
[snip]
>> Hmmmm ... I see where you're coming from. You observe that all modern species
>> of elphants have bigger ears than their ancestors and their modern cousins
>> such as manatees, dugongs, and hyraxes. This leads you to the conclusion that
>> large ears are an adaptation. However, if the ancestors of modern elephants
>> just happened to have large ears, and large ears were not a disadvantage,
>> then the presence of large ears could just as easily be due to drift. The
>> fact that modern species possess a certain characteristic feature is not
>> prima facie evidence of adaptation since drift and the founder effect would
>> achieve the same result.
>
> True, but the advantage of large ears in a large mammal that can't
> really stay out of the tropical sun is obvious.
Not obvious to me. There are all kinds of species that inhabit similar
environments but don't have big ears.
> Why would you think that big ears would be a random occurrence?
It's a reasonable hypothesis. My main point is to simulate people into
recognizing the possibility instead of blindly attributing everything
to selection.
> Drift is probably a minor
> effect, while founders are interesting because of the advantage that
> made them a new species not because of their random minor traits.
I understand that you think of random genetic drift as a trivial process
in evolution. I'm hoping to get you to examine that assumption.
>> But that's not what I had in mind. I was referring to the fact that Asian
>> elephants have much smaller ears than African elephants. If ear size is
>> under strong selection then one has to account for this fact. On the other
>> hand, if ear size is non-adaptive then the difference between Asian and
>> African elephants could be due entirely to chance.
>
> Gee, why don't humans have large ears if they are just by chance?
Are you serious? Do you understand what chance is?
> Ever think that climate differences account for the smaller ears in
> Indian elephants?
That's a characteristic response from an adaptionist. Whenever you're
faced with new bits of information you make up a new just-so story to
support adaptation. Start thinking about other possibilities.
> There's no reason to believe that non-adaptive mutations lead to
> speciation - and that's where all the marbles are.
I can see that you're not familiar with modern evolutionary theory
of speciation. I suggest you read any of the standard textbooks on
evolution. The section on allopatric speciation should be most
informative.
[snip]
>>>Considering genetic diversity, itself, gives a species an advantage,
>>>you're going to have to explain why traits would develop for
>>>non-adaptive reasons.
>>
>>
>> Two points ...
>>
>> 1. Genetic diversity cannot be an adaptation since this requires a form
>> of group selection that has been thoroughly discredited. If a species
>> accidently possesses more diversity then it will be the lucky survivor
>> when the environment changes. This is more like evolution by chance
>> that real adaptation.
>
> Discredited? We all know that in many species that have familial
> groups, say lions, the males leave or are expelled from the group to
> find mates elsewhere. That type of behavior occurs across many
> species with the obvious effect of diversifying the genetics. I seem
> to recall research that showed that pheromones may play a role in
> selecting a mate with different characteristics even in humans.
You can't select for future events. While it's true that diversity within
a species might pay off when the environment changes, it's not true
that you can *select* for diversity on the off-chance that it will be
beneficial sometime in the future. That kind of group selection has
been discredited.
>> 2. All kinds of traits can arise by chance. Take the ability of some
>> people to roll their tongues as a simple example. Why do I have
>> to explain why traits would develop for non-adaptive reasons? Is
>> it because of your (irrational) belief that everything MUST be
>> an adaptation?
>
> Not everything is an adaptation, but adaptation plays a much more
> important role than chance.
I understand that you think this. I'm hoping to get you to re-examine
that faith.
[snip]
> Adaptations ARE evolution. Evolution doesn't care about junk DNA or
> mutations that are neutral from the perspective of natural selection.
Sorry, you don't get to redefine evolution to suit your personal
prejudices.
>> 2. The most reasonable minimal definition of evolution is change in
>> the frequency of heritable characteristics in a population over
>> time. This definition includes fixation by random genetic drift of
>> almost neutral alleles. You seem to want to change that definition
>> to restrict it to changes in phenotype - where presumably you mean
>> only observable phenotypes. Furthermore, when you say that this is
>> "all that evolution can work" with you imply that evolution is
>> synonomous with natural selection. In other words, you would like to
>> change the definition of evolution so that the only "real" evolution
>> is adaptation. This is consistent with the fact that you aren't
>> interested in any other kind of evolution but here you go one step
>> farther. Now you are suggesting that we re-define evolution so
>> that my interests become illegitimate. If you succeed (highly
>> unlikely) then what word will you use for all those heritable changes
>> that aren't adaptations? Will this be pseudoevolution? :-)
>
> Your interests aren't "illegitimate," they are other aspects of
> biology. But genetic drift isn't important to evolution, junk DNA and
> other unexpressed genes aren't either. Biology and genetics are areas
> that hold other intrinsic interest. Why are you trying to shoehorn
> all of biology into the study of evolution?
I understand that you aren't interested in any kind of evolution that
doesn't involve adaptation. I don't share your narrow approach to
what's interesting in evolution.
>>>>and evolution by accident.
>>>
>>>Evolution by accident? Can you explain?
>>
>> Yes, I'm referring to evolution that takes place without natural selection
>> playing a significnat role. It includes things such as the random
>> elimination of some species, and the survival of others, at the time of
>> mass extinctions. (The so-called "Field of Bullets" senario of David Raup.)
>
> Something usually causes mass extinctions. A significant stressor.
> It may or may not be transitory. But I suspect that, for the most
> part, we can find common characteristics among the surviving species
> that would explain why they survived. I have my doubts that things
> are totally random.
That's a typical answer from an adaptionist. When faced with a question
about evolution (e.g., the results of mass extinctions) the first (only?)
response is an adaptionist just-so story. I'm hoping to convince you that
there are other possibilities worth considering. Do you have any idea
what the "Field of Bullets" scenario is all about?
>> It includes lots of other things as well. When I use the phrase "evolution
>> by accident" I mean it to be a direct contrast to adaptionism. The phrase
>> is intended to provoke people into thinking outside their box. (It's
>> also a convenient way to emphasize the contrast between real evolution and
>> intelligent design.)
>
> Ah, curiosities for arguing with Luddites. Can you actually convince
> them of anything?
I'm not having any luck here. You need to abandon your old-fashioned out-
dated view of evolution and move into the 21st century.
>>>>I'm not having
>>>>much luck on sci.bio.evolution. This newsgroup is heavily dominated
>>>>by people who reject the very concept of drift or who have deliberately
>>>>chosen not to understand it. I find this very strange in a newsgroup
>>>>that's supposed to be devoted to discussing evolution at a serious
>>>>level.
>>>
>>>Maybe because "drift" doesn't seem to be very well defined.
>>
>> Not true. It's as well-defined as natural selection. It may be a more
>> difficult concept to grasp and it may be unfamiliar to those who have
>> been brought up on a steady diet of adaptionist dogma, but that's a
>> different kettle of fish. You can't dismiss random genetic drift just
>> because you don't understand it.
>
> I can dismiss it because it's not significant in evolution. You
> haven't shown any method by which it would cause speciation.
You don't know much about evolution, do you?
Larry Moran
Steve Schaffner
> The quantitly of relevance of the calculaton is known as the
> "effective populaton size".
>
> An effective population size of 500 is considered to be a threshold
> for status as an endangered species.
>
> The figures you are talking about (in isolated populations) would
> represent effective population sizes of 25-50 - putting them straight
> into the red, flashing region of the endangered species list.
>
> It is true that we are in the middle of a mass extinction at the momement
> - and so it's inevitable that more than the usual number of species are
> going through small population sizes as part of the process of
> shuffling off this mortal coil.
>
> However, the population sizes you talk about still seem to be very low.
Those are low for effective population sizes, at least for most
species. Larger numbers lead to the same conclusion, however. A
population size of five or ten thousand leads to marked genetic drift
over a few thousand generations. Genetic drift is also responsible
for eliminating most new selectively favored mutations, whatever the
population size.
--
Steve Schaffner s...@broad.mit.edu
Immediate assurance is an excellent sign of probable lack of
insight into the topic. Josiah Royce
Steve Schaffner
> Adaptations ARE evolution. Evolution doesn't care about junk DNA or
> mutations that are neutral from the perspective of natural selection.
[...]
> Your interests aren't "illegitimate," they are other aspects of
> biology. But genetic drift isn't important to evolution, junk DNA and
> other unexpressed genes aren't either. Biology and genetics are areas
> that hold other intrinsic interest. Why are you trying to shoehorn
> all of biology into the study of evolution?
You are free to invent whatever meanings you like for words, but if
you want to communicate with others, you'll have to use standard
definitions. Neutral evolution, and genetic drift more generally, are
part of evolution as evolutionary biologists use the term. Molecular
evolution, in particular, studies changes in DNA (or DNA products),
regardless of whether those changes are the result of selection or
not. I have no idea how you could model adaptive evolution without
also modelling genetic drift -- evolution is an inherently stochastic
process.
> I can dismiss it because it's not significant in evolution. You
> haven't shown any method by which it would cause speciation.
Geographic isolation and genetic drift are pretty much guaranteed to
cause speciation eventually. Whether drift is in fact a major
contributor to speciation is an empirical question, but there's no
doubt that it can produce speciation.
Larry Moran
> news:c1tbc9$8hi$1...@darwin.ediacara.org:
[snip]
>> Hmmmm .... I would have thought that ear size in elephants and skin
>> color in humans were excellent example of drift. Don't you see how
>> difficult it is to make general rules? Your decision about what the
>> "default" hypothesis should be depends to a great extent on your
>> original biases. This is exactly the point that Lewontin and Gould
>> made in their original paper. If you tend to emphasize natural
>> selection in your thinking about evolution then you will look to
>> adaptive explanations ahead of non-adaptive explanations.
>
> I will stand by my example of ear size in elephants - my reference is a
> book entitled "Why Elephants Have Big Ears" - which despite its title was
> written by Chris Lavers, not Rudyard Kipling :-) In another follow on
> this thread you questioned why Indian elephants have smaller ears. Lavers
> notes that both Indian elephants and African forest elephants - both of
> which have smaller ears than African savanna elephants - inhabit forests
> with lower temperatures than the savanna. He also notes that woolly
> mammoths had tiny ears.
I have't read the book.
How does one distinguish between a just-so story and a valid explanation?
If it turned out that Asian elephants had big ears and African elephants
had small ones do you think that someone would come up with an adaptionist
explanation? I do. That's the problem. With sufficient imagination one can
conjure up an adaptionist explanation for almost anything that happens in
biology. This isn't a very good reason for preferring adaptionist explanations
over chance and accident - expecially since we know for a fact that chance
plays the major role at the molecular level. Why shouldn't it play a major
role at the morphological level as well?
> Skin color in humans is obviously controversial, but is a very
> interesting example. AFAIK skin pigmentation is fairly well correlated
> with latitude in the Old World, even among populations with rather
> different origins, e.g. Indo-Europeans in India and Bantu speakers in
> central Africa. And there is a plausible explanation for this - the
> balance between Vitamin D production and folate production. However there
> is little variation with latitude in the New World - probably an example
> of founder effect - while there is considerable variation among
> relatively isolated island populations in New Guinea - probably an
> example of sampling error.
So, is it possible that variation in skin color is due to selection in
some parts of the world (Northern Europe) but drift elsewhere?
>>> Note that I am cheating somewhat, as I am assuming there is at
>>> least some data available to make a "default" assumption.
>>
>> Part of the problem is that even the selection of "data" has
>> built-in biases. If you are an adaptionist, and you prefer an
>> adaptionist explanation, then you go looking for data to support
>> your assumption.
>
> Of course - that's how science works. Fortunately for me there are people
> like you that prefer stochastic explanations and try to poke holes in my
> data while finding data that support your assumptions. As long as we are
> polite in our discourse, honest in our data, and don't exclude from the
> table those with ideas out of the mainstream, the system works pretty
> well.
This is exactly right. There should always be healthy debate over the
various explanations of the data. This requires that everyone accept the
main principles of evolutionary theory - especially that random gentic
drift is a known mechanism. It's fun to discuss this with you but it's
very frustrating to have a similar discussion with someone who doesn't
even accept the existence of random genetic drift.
(A minor quibble ... natural selection also has a major stochastic
component. Most beneficial mutations are eliminated from the population.
The best you can do is calulate the "probability" that a given allele
will become fixed if you know the selection coefficient.)
>> No offense. I'm a drifter in the sense that it's part of my
>> self-proclaimed "mission" to educate people about the importance
>> of random genetic drift and evolution by accident. I'm not having
>> much luck on sci.bio.evolution. This newsgroup is heavily dominated
>> by people who reject the very concept of drift or who have
>> deliberately chosen not to understand it. I find this very strange in
>> a newsgroup that's supposed to be devoted to discussing evolution at a
>> serious level.
>
> See my comment above. In fact, while I still (as you have undoubtedly
> noted) have a strong adaptationist bias, I have learned a lot about drift
> from discussions on this newsgroup, which have often lead me to do
> further reading. You noted in another follow that you are interested in
> the mechanism of speciation. While I can keep hoping, I have not seen any
> convincing explanations based on adaptation for the extent and pace of
> speciation. Adaptive explanations may explain _why_ there should be two
> different niches available for sticklebacks in Canadian lakes, but not
> _how_ one species could rapidly diversify to fill both niches. But it is
> getting late, so perhaps I will leave further discussion of that topic
> for another day.
Okay.
Larry Moran
Larry Moran
Anon. <bob....@SOD.OFF.Spammers.helsinki.fi> wrote:
> Larry Moran wrote:
[snip]
>> Two points ...
>>
>> 1. Genetic diversity cannot be an adaptation since this requires a form
>> of group selection that has been thoroughly discredited. If a species
>> accidently possesses more diversity then it will be the lucky survivor
>> when the environment changes. This is more like evolution by chance
>> that real adaptation.
>>
> Two points ...
> 1. Inbreeding depression is a form of lack of genetic diversity that can
> increase the chance that a population goe extinct. This will generally
> work at low effective population sizes.
This is correct but that's not the point. The point is whether you can
*select* for diversity within a population based on the assumption that
it will become useful at some future date. Similary, the lack of genetic
diversity might not be a problem in a stable environment. What's to prevent
a species from going this route by chance? You can't warn it that this is
a bad idea for its future ancestors. Species tend not to listen to such
arguments. (Especially those with small ears!)
> 2. If you view diversity as a trait of a group, and has sufficiently
> high "heritability" (i.e. heritability at the group level), then it can
> evolve. For example, if the environment keeps on changing. To be
> honest, I doubt this is a major force in evolution, but it might work in
> some cases, for example with species competing against each other. This
> is an example of the sort of group selection that hasn't been
> discredited (yet) - trait group selection.
Hmmm .... that's a bit different. Now you're talking about species sorting
and not group selection. I assumed that the original comment referred to
diverity within a population and not diversity within a clade. I'm
curious, but agnostic, about species sorting even though I've read every
page of "The Structure of Evolutionary Theory."
Larry Moran
Tim Tyler
> I will stand by my example of ear size in elephants - my reference is a
> book entitled "Why Elephants Have Big Ears" - which despite its title was
> written by Chris Lavers, not Rudyard Kipling :-)
Lest anyone get the wrong idea, this is the title of one of the essays
in the book (the first one) - not a whole book about elephant ears ;-)
> Skin color in humans is obviously controversial, but is a very
> interesting example. AFAIK skin pigmentation is fairly well correlated
> with latitude in the Old World, even among populations with rather
> different origins, e.g. Indo-Europeans in India and Bantu speakers in
> central Africa. And there is a plausible explanation for this - the
> balance between Vitamin D production and folate production. However there
> is little variation with latitude in the New World - probably an example
> of founder effect - while there is considerable variation among
> relatively isolated island populations in New Guinea - probably an
> example of sampling error.
Well put.
Here it is mostly the individuals that are doing the drifting ;-)
> Adaptive explanations may explain _why_ there should be two
> different niches available for sticklebacks in Canadian lakes, but not
> _how_ one species could rapidly diversify to fill both niches. But it is
> getting late, so perhaps I will leave further discussion of that topic
> for another day.
There is "divergent selection" to consider:
When two species are only partially inter-fertile, selection can act
to reinforce mating cues that allow individuals to distingush members
of the other species - to avoid costly failed offspring.
Also, species-level selection may have something to say about the issue.
Tim Tyler
> Hrm, changes in ecosystems happen - sometimes rapidly - due to
> geological processes and species must either adapt or die out. That's
> evolution. Evolution isn't always driven by advantageous mutations of
> species within a stable ecosystem. You're not proposing any
> significant change in the theory, just applying it to species in
> extremis.
Genetic drift is /already/ part of the theory of evolution.
Far from not being "very well defined", it is defined clearly
in all the textbooks. Check it out.
Tim Tyler
> > They can remain fixed due to selective lock-in if other adaptations
> > come to depend on their presence.
>
> In which case they will still show little variation in large populations
> - but those populations will also give more opportunity for competing
> suites of adaptations to develop and overcome the lock-in.
Overcoming lock-ins is difficult. That's why they are so called.
> > Old, non-variable traits (of any sort) need not /necessarily/
> > represent adaptations.
>
> I disagree strongly. If they are not being fixed by stabilizing
> selection, they will drift.
You criticism doesn't address my point, though. Locked-in accidents
*are* kept in place by stabilizing selection. If they change, then
all the adaptations that depend on them crash.
Your criticsim only deals with traits *not* fixed by stabilising selection.
A locked-in accident is certainly not like that. Attempts to change
such traits meet strong resitsance from selection.
However that does not mean they didn't originally arise from the founder
effect - or some such - and at the time they first formed, they may well
have been near-neutral.
[snip blood types]
Tim Tyler
> > Jeffrey Turner <jtu...@localnet.com> wrote:
> Adaptations ARE evolution. Evolution doesn't care about junk DNA or
> mutations that are neutral from the perspective of natural selection.
They are evolution as well - by the *definition* of the term.
> >>Maybe because "drift" doesn't seem to be very well defined.
> >
> > Not true. It's as well-defined as natural selection. It may be a more
> > difficult concept to grasp and it may be unfamiliar to those who have
> > been brought up on a steady diet of adaptionist dogma, but that's a
> > different kettle of fish. You can't dismiss random genetic drift just
> > because you don't understand it.
>
> I can dismiss it because it's not significant in evolution. You
> haven't shown any method by which it would cause speciation.
Nor should he have to.
Island speciation represents an instance of drift causing speciation.
Tim Tyler
> > Guy Hoelzer <hoe...@unr.edu> wrote or quoted:
> > > in article c1nrui$1dba$1...@darwin.ediacara.org, R.Schenck at
> > > > Guy Hoelzer <hoe...@unr.edu> wrote in message
[...]
> > Having said that, natural selection is /still/ pretty fundamental.
> >
> > Since it gets to decide which self-organising systems exist and
> > which don't, it pretty-much has the final word.
> >
> > In the future we will see completely new ways for adaptions to
> > arise in organisms - namely they will be designed and engineered
> > to be there - the products of "mutations" directed by intelligent
> > design - but even then, natural selection will still preside over
> > everything.
>
> Natural selection does not and will not preside over everything. It
> doesn't have any influence over those phenotypical features that are
> neutral and don't affect the ability of an organism to reproduce.
> Some of us believe that this constitutes the majority of features
> observed, whether those features were produced by genetic drift or are
> accidental side effects like spandrels, or are results of
> self-organizing processes.
A king can still rule a land - without decreeing whether the subjects
part their hair to the left or to the right.
> The new ways you're talking about also won't necessarily be affected
> by natural selection either. Consider genetic engineering to boost the
> intelligence of humans. Humans with IQ's of 250 are not necessarily
> going to produce more children than those with IQ's of 95. In fact
> they may think that the intelligent thing is not to have
> children at all. Natural selection can only act where there is
> differential success in producing offspring. Yet here we can have a
> case where there can be a constant, or perhaps even increasing number
> of IQ 250 humans independent of the reproductive success of those
> humans. How? By genetic engineering of the sperm or eggs of those
> ordinary IQ humans who wish to have enhanced children.
Natural selection would still be completely in charge. The only way
I can see to unseat natural selection is the way I describe on:
http://alife.co.uk/misc/one_big_organism/
If you can do that - or something closely equivalent - then it's the end
for competition - at least for a little while. Otherwise living things
will remain subject to selective forces.
phillip smith
wdm...@twcny.rr.com wrote on 4/3/04 5:51 AM:
> While I can keep hoping, I have not seen any
> convincing explanations based on adaptation for the extent and pace of
> speciation.
Simple, speciation is adaptive !
--
Phillip Smith
phills@(buggger).co.nz replace bugger with ihug
http://www.applied-evolution.co.nz
"he who is smeared with blubber has the kindest heart" -- a Greenland Eskimo
adage
Jim Menegay
> [snip]
> IMHO, if Dawkins and his followers continue to ignore the overwhelming
> evidence of adaptive "evolution" in complex dynamical systems that seemingly
> lack the basic ingredients for the process of natural selection (e.g.,
> populations of reproducing agents), they will look increasingly like
> closed-minded zealots as time goes on.
> [snip]
This interests me, but puzzles me. What does "adaptive" mean in this
context? I have a picture of a system (without reproducing parts) getting
better at something - presumably something that is in its own best interests.
But I don't see in what sense a dynamical system can be said to have
interests.
Also, I wonder what "complex" means in this context. Presumably, dynamical
systems that are not complex don't exhibit this phenomenon of adaptive
evolution. But what is complexity? Does it come from the large number
of dimensions in the state space? The strangeness of the attractors? Our
lack of understanding of how the system works?
(Or did I misunderstand the "e.g."? Are you saying that a population of
reproducing, but non-mutating, agents will evolve adaptively? One model of
this, of course, would be Daisy World.)
Tim Tyler
> > Larry Moran wrote:
> >> 1. Genetic diversity cannot be an adaptation since this requires a form
> >> of group selection that has been thoroughly discredited. [...]
>
> This is correct but that's not the point. The point is whether you can
> *select* for diversity within a population based on the assumption that
> it will become useful at some future date.
The point seemed to be that "genetic diversity cannot be an adaptation".
The adaptive mechanism that produces diversity doesn't /have/
to select on the basis that diversity will be useful in the
future. It can favour diversity on the grounds that making
offspring systematically different from yourself will reduce
the chance of them being susceptible to the most common
parasites. A rather short term effect, requiring no precognition.
> Similary, the lack of genetic diversity might not be a
> problem in a stable environment. What's to prevent a
> species from going this route by chance? You can't warn
> it that this is a bad idea for its future ancestors.
For most species, there's no such thing as a stable environment.
That's because one of the components in their environment is
a seething pool of parasites. These are in constant flux -
and adapt to attack the most common genotype - resulting in
powerful frequency-dependent selection for being of a rare
breed.
Species can't usually reach stability by eliminating their
parasites. Practically all species of large organisms have
plenty of parasites - and if parasites are ever rare, the cost
of defending against them goes down - so soon, the parasites
become more numerous again.
Anon.
The usual adaptive explanation for this behaviour is that it reduces
kin-kin competition, so that it may have nothing to do with diversity.
Come to that, this behaviour may not have an effect on diversity at the
species level, but only on how it is distributed.
<snip>
>>>>I'm not having
>>>>much luck on sci.bio.evolution. This newsgroup is heavily dominated
>>>>by people who reject the very concept of drift or who have deliberately
>>>>chosen not to understand it. I find this very strange in a newsgroup
>>>>that's supposed to be devoted to discussing evolution at a serious
>>>>level.
>>>
>>>Maybe because "drift" doesn't seem to be very well defined.
>>
>>Not true. It's as well-defined as natural selection. It may be a more
>>difficult concept to grasp and it may be unfamiliar to those who have
>>been brought up on a steady diet of adaptionist dogma, but that's a
>>different kettle of fish. You can't dismiss random genetic drift just
>>because you don't understand it.
>
>
> I can dismiss it because it's not significant in evolution. You
> haven't shown any method by which it would cause speciation.
>
I don't know if Larry knows (or cares) about the genetics of allopatric
speciation, but that I interpret that evidence as showing that
speciation occurs through two populations becoming physically isolated,
and then becoming genetically isolated through drift.
Jim Menegay
I agree with Tim. And I suspect that there are many other species-level
traits that might promote diversity.
The standard way of thoroughly discrediting group selection is to point
out that selection at the level of individuals would "trump" the much
weaker process at the group level. But in this case particularly, that
argument doesn't seem to apply. What could a selfish individual possibly
do that would subvert the species from carrying out its strategy of
genetic diversity?
TomHendricks474
to select on the basis that diversity will be useful in the
future. >>
I suggest this general rule:
As adaptive fitness increases stabilizing selection increases and directional
and diversifying selection decreases,
and vice versa.
As adaptive fitness decreases
stabilizing selection decreases and directional and diversifying selection
increases.
Tim Tyler
> > [snip]
> > IMHO, if Dawkins and his followers continue to ignore the overwhelming
> > evidence of adaptive "evolution" in complex dynamical systems that seemingly
> > lack the basic ingredients for the process of natural selection (e.g.,
> > populations of reproducing agents), they will look increasingly like
> > closed-minded zealots as time goes on.
> > [snip]
>
> This interests me, but puzzles me. What does "adaptive" mean in this
> context? I have a picture of a system (without reproducing parts) getting
> better at something - presumably something that is in its own best interests.
> But I don't see in what sense a dynamical system can be said to have
> interests.
A brain is a complex adaptive system - it changes over time in a manner
that matches and reflects elements in its environment.
You don't have to be able to self-reproduce to be able to adapt -
since there are other ways of adapting besides natural selection -
e.g. learning.
Tim Tyler
> The standard way of thoroughly discrediting group selection is to point
> out that selection at the level of individuals would "trump" the much
> weaker process at the group level. But in this case particularly, that
> argument doesn't seem to apply. What could a selfish individual possibly
> do that would subvert the species from carrying out its strategy of
> genetic diversity?
It's going to look as though I am playing both sides of this - but:
In asexual species, diversity is a function of the uncorrected mutation
rate.
Individuals can control their mutation rates to some extent - by choosing
to what extent they invest in clean-burn technology, and clean-up
technology.
According to genetic-algorithm folklore, a population will best explore
the fitness landscape if there's about one mutation per individual per
generation. I figure this is what species selection would probably
favour.
However, individuals benefit most from avoiding mutations completely -
since often mutataions lead to broken offspring.
In some single-celled organisms, I've read [sorry no reference today] that
the individual gets its way. The mutation rate is *much* lower (by a
couple of orders of magnitude) than it should be if the species wanted to
be able to evolve rapdily in the face of a changing environment.
Here, the individuals could do something to stop diversity arising -
namely lower their mutation rates to *extremely* low levels.
Apparently, sometimes that's exactly what they do.
TomHendricks474
over chance and accident - expecially since we know for a fact that chance
plays the major role at the molecular level. Why shouldn't it play a major
role at the morphological level as well? >>
There is good reason still to question that chance
plays the major role at the molecular level.
If every aspect of life evolves in a cyclical temperature environment, then how
can randomness evolve out of a non randon environment?
It would be more correct to say that it has some random
and some non random parts.
I agree with all your points, but I think the cyclical environmental
temperature
may play a bigger part on the molecular level than most think now.
William Morse
> William Morse <wdm...@twcny.rr.com> wrote or quoted:
>> Tim Tyler <t...@tt1lock.org> wrote in
>> > Old, non-variable traits (of any sort) need not /necessarily/
>> > represent adaptations.
>>
>> I disagree strongly. If they are not being fixed by stabilizing
>> selection, they will drift.
>
> You criticism doesn't address my point, though. Locked-in accidents
> *are* kept in place by stabilizing selection. If they change, then
> all the adaptations that depend on them crash.
>
> Your criticsim only deals with traits *not* fixed by stabilising
> selection.
>
> A locked-in accident is certainly not like that. Attempts to change
> such traits meet strong resitsance from selection.
>
> However that does not mean they didn't originally arise from the
> founder effect - or some such - and at the time they first formed,
> they may well have been near-neutral.
> [snip blood types]
Sorry- I misread you. Even though you specifically discussed lock-ins, I
read it as linkage - which can also limit variation in selectively
neutral traits but which is subject to unlinkage given enough time or a
large enough population. I will concede that lock-ins are an exception to
my default assumptions - but fortunately for myself I _did_ point out
that they were only assumptions, subject to correction by better data:-)
And I will further note that non-adaptive lock-ins are unlikely to
represent very many traits in old, widespread, morphologically stable
species, because such species are still subject to competition from other
species and have been for a long time. So they cannot afford too much
extra baggage.
Yours,
Bill Morse
Tim Tyler
> And I will further note that non-adaptive lock-ins are unlikely to
> represent very many traits in old, widespread, morphologically stable
> species, because such species are still subject to competition from other
> species and have been for a long time. So they cannot afford too much
> extra baggage.
What if - after not very long - all their competition comes from other
organisms with the same lock-in?
I fully expect this is the case regarding a number of old, widespread and
stable adaptations - such as the genetic code.
I don't want to give too much weight to non-adaptive traits - but frozen
accidents are certainly possible.
Jeffrey Turner
If chance and accident were the overriding determiners, then we would
expect greater variety. Why shouldn't there be three species of
elephant on the African savannah, or seven or twenty? Why don't
animals come in all sorts of random shapes and sizes? Why have
speciation at all? Where _are_ the small eared African savannah
elephants? If there aren't advantages to adaptations why have
evolution at all?
--Jeff
--
A man, a plan, a cat, a canal - Panama!
Ho, ho, ho, hee, hee, hee
and a couple of ha, ha, has;
That's how we pass the day away,
in the merry old land of Oz.
Guy Hoelzer
jimme...@sbcglobal.net wrote on 3/4/04 8:39 AM:
> Guy Hoelzer <hoe...@unr.edu> wrote in message
> news:<c1dfif$143o$1...@darwin.ediacara.org>...
>
>> [snip]
>> IMHO, if Dawkins and his followers continue to ignore the overwhelming
>> evidence of adaptive "evolution" in complex dynamical systems that seemingly
>> lack the basic ingredients for the process of natural selection (e.g.,
>> populations of reproducing agents), they will look increasingly like
>> closed-minded zealots as time goes on.
>> [snip]
>
> This interests me, but puzzles me. What does "adaptive" mean in this
> context? I have a picture of a system (without reproducing parts) getting
> better at something - presumably something that is in its own best interests.
> But I don't see in what sense a dynamical system can be said to have
> interests.
I agree with your intuition about how to conceive of adaptation as something
not limited to biological populations. Note that I think of this
hierarchically, so that any explanation of self-interest in the bigger
picture should apply fully to our narrower understanding of self-interest in
the biological context. I see non-equilibrial thermodynamics as explaining
the notion of self-interest most generally.
Your concern about the nature of self-interest in non-biological, dynamical
systems is understandable; but interestingly I think that most evolutionary
biologists would have a similar problem with the notion of self-interest at
the level of populations of biological organisms, which is exactly the level
at which they are most comfortable with the notion of natural selection as
the adaptive process. The general claim of the theory of complex adaptive
systems, as I see it, is that they emerge (manifest) because they serve a
thermodynamic imperative. The teleological aspect of service thus imbues
all dynamical systems with self-interest in a sense that does not require
anything like cognition.
> Also, I wonder what "complex" means in this context. Presumably, dynamical
> systems that are not complex don't exhibit this phenomenon of adaptive
> evolution.
Well -- the theory as I understand it suggests that there cannot be such a
thing as a simple dynamical system. Complexity (decentralized control in
networks of interacting parts) is claimed to be a co-requisite for the
emergence of systematic (coherent) functional activity.
> But what is complexity? Does it come from the large number
> of dimensions in the state space? The strangeness of the attractors? Our
> lack of understanding of how the system works?
It is emphatically not about our lack of understanding, although it can be
harder to understand the inner workings of complex systems than it is to
understand simple relations. I hope my explanation above suggests the
conceptual links of complexity with dimensionality and strange attractors.
> (Or did I misunderstand the "e.g."? Are you saying that a population of
> reproducing, but non-mutating, agents will evolve adaptively? One model of
> this, of course, would be Daisy World.)
No; you seem to have understood my "e.g." correctly, although I agree with
your point.
Cheers,
Guy
Jim Menegay
But would you say that the motion of the planets around the sun is a kind
of self-interest because it serves a gravitational imperative? I don't
think so.
NeoDarwinism is sometimes characterized by the slogan that "Genes mutate,
individuals are selected, and species evolve". It might be added that
the end result of this evolution is that the typical individual is
adapted. But, "adaptation" for a complex system must apply to the same
entity that evolves - namely the system itself. There are no lower level
entities. Are you saying that NeoPrigoginism's slogan would be "Systems
evolve, systems become adapted"? Or, are you saying that complex systems
are automatically adaptive (adapted?) - they don't need to evolve to
become adapted? As you can see, I am struggling here to come up with
some analogy with Evolution/NaturalSelection that lets me categorize your
viewpoint and usee of the word "adapt".
Let me suggest that thermodynamic systems far from equilibrium sometimes
exhibit a kind of "self organization" and you might say that they have an
interest in maintaining that organization. I am still a little
uncomfortable with using the word "adaptive" to describe this hypothetical
behavior by a complex system. It seems to be little more than a kind
of (meta)stability. I am also not yet convinced that the inevitable
appearance of this kind of behavior is backed by "overwhelming evidence"
>
> > Also, I wonder what "complex" means in this context. Presumably, dynamical
> > systems that are not complex don't exhibit this phenomenon of adaptive
> > evolution.
>
> Well -- the theory as I understand it suggests that there cannot be such a
> thing as a simple dynamical system. Complexity (decentralized control in
> networks of interacting parts) is claimed to be a co-requisite for the
> emergence of systematic (coherent) functional activity.
You are apparently reading different texts than I am. My sources use the
term dynamical system for simple systems such as pendula and two-body
orbital mechanics problems. But this is merely a quibble over terminology.
>
> > But what is complexity? Does it come from the large number
> > of dimensions in the state space? The strangeness of the attractors? Our
> > lack of understanding of how the system works?
>
> It is emphatically not about our lack of understanding, although it can be
> harder to understand the inner workings of complex systems than it is to
> understand simple relations. I hope my explanation above suggests the
> conceptual links of complexity with dimensionality and strange attractors.
>
> > (Or did I misunderstand the "e.g."? Are you saying that a population of
> > reproducing, but non-mutating, agents will evolve adaptively? One model of
> > this, of course, would be Daisy World.)
>
> No; you seem to have understood my "e.g." correctly, although I agree with
> your point.
I'm happy that you agree with me, but I'm not sure I successfully
communicated my point. Daisy World is a crock IMHO. Lovelock created an
artificial model to illustrate the kinds of mechanisms that might lead
to a Gaian homeostasis. But it would be just as easy to create a model
of a world that doesn't exhibit homeostasis - that is actively unstable.
TomHendricks474
*select* for diversity within a population based on the assumption that
it will become useful at some future date. >>
I couldn't agree with this more.
It is a basic argument for every aspect of selection.
So why does everyone throw it right out the window when it comes to prebiotic
chemistry selection?
Shouldn't every step of the way, every day of the origin, be that day's
prebiotic chemistry selection - and not for some want-to-reach event later?
How could it be otherwise? If otherwise - explain .
The most obvious misuse of this is that amino acids acted as they did 4 billion
years ago to get to the 20 we need today.
How many times have you read a version of that?
I would contend that every step of the origin was a prebiotic chemical selected
advantage for that very day - and so we look at what forces pushed selection 4
billion years ago not at what it became later.
(and as most know by now I come up with cyclic heat cycle as that force)
Jim Menegay
But the brain is an evolved mechanism. Sure, systems that have been
constructed by evolution or by intelligent design can be adaptive. The
adaptiveness of such systems arises from their genesis, not from their
complexity. I thought that the issue was whether there is some sort of
compulsion or tendency of complex systems to become adaptive.
Jim Menegay
> On Wed, 3 Mar 2004 16:51:17 +0000 (UTC),
> Anon. <bob....@SOD.OFF.Spammers.helsinki.fi> wrote:
> > Larry Moran wrote:
>
> [snip]
>
> >> Two points ...
> >>
> >> 1. Genetic diversity cannot be an adaptation since this requires a form
> >> of group selection that has been thoroughly discredited. If a species
> >> accidently possesses more diversity then it will be the lucky survivor
> >> when the environment changes. This is more like evolution by chance
> >> that real adaptation.
> >>
> > Two points ...
> > 1. Inbreeding depression is a form of lack of genetic diversity that can
>
> This is correct but that's not the point. The point is whether you can
> *select* for diversity within a population based on the assumption that
> it will become useful at some future date.
This discussion involves an intricate interplay of several ideas
1. Species selection vs individual selection.
2. Selection vs drift
3. Long term vs short term.
I hope I don't complicate things more by introducing a fourth issue - the
dreaded Haldane's dilemma.
My take on HD is that it points out that selection has a lot of work to
do killing off the unfit, and only a finite time to do it. Selective
deaths are a scarce resource, and natural selection is unlikely to waste
them on trivial things like optimizing the size of an elephant's ears -
especially since there has only been a short time since African and Indian
elephants diverged.
That is, I am taking HD as an argument against extreme adaptationism.
But HD is also applicable to the question of long term vs short term.
If a trait is disadvantageous in the short term, but advantageous in the
long term, should we expect the trait to persist in a population? Sure,
why not, suggests HD, as long as the short term disadvantage is small in
comparison with the other issues that selection has to deal with.
That is, I am suggesting here that the orthodox belief in the idea that
the short term always trumps the long term is probably wrong. Long term
advantageous traits, for example a mutation rate slightly larger than
the short term optimum, can be selected for in the face of a short term
disadvantage.
Consider the population just after one of the sporadic long term events.
For example, look at it just after a major attack by a new virus. The
survivors were lucky in having a high mutation rate that let them "respond"
to the attack. So the population at this point in time will have a high
mutation rate. But, this high mutation rate is disadvantageous in the
short term, so we can expect it to decline under selection. But HD says
that the rate of decline will be finite. If the trait of a high mutation
rate is not totally extinguished by short term selection before the next
big virus attack, then long term selective pressure can win over short
term selective pressure. And, if it doesn't win, then it could be claimed
that there wasn't really any long term advantage to begin with.
TomHendricks474
NeoDarwinism is sometimes characterized by the slogan that "Genes mutate,
individuals are selected, and species evolve". >>
Nothing is simple. What if there is selection on
GC base pair over AT base pair?
GC is often found in stems where stability is an
important trait.
Is it being selected for on that basis?
Tom
TomHendricks474
Daisy World is a crock IMHO. Lovelock created an
artificial model to illustrate the kinds of mechanisms that might lead
to a Gaian homeostasis. But it would be just as easy to create a model
of a world that doesn't exhibit homeostasis - that is actively unstable.
>>
I challenge you on that. Give an example.
I think you will find that with out variations in the environment you won't
have variants to select from, and more importantly there will be no cyclic
predictable force for a chemistry system to adapt to - which is what life is
IMO.
Tom
Jim Menegay
But it is the individual that benefits if it has a high mutation rate
and it lucks out by coming up with just the mutation that is needed.
Hmmm... But the species also benefits in some sense. All the other
low mutation rate individuals in the population have the opportunity
to recombine with the mutant. So, they may have some reason to encourage
the altruistic mutator and to provide some kind of compensation.
What do you know... They do compensate. They assume a share of the risks
of mutation; their descendents will occasionally get a double dose of
recessive lethals. In this viewpoint, sex is a species level system which
creates a kind of reciprocity between high mutation-rate individuals and
low mutation-rate individuals.
This idea is new to me, but it can't be new. Has anyone seen anything like
this in the literature.
Larry Moran
Jim Menegay <jimme...@sbcglobal.net> wrote:
[snip]
> I hope I don't complicate things more by introducing a fourth issue
> - the dreaded Haldane's dilemma.
You did complicate things by introducing "Haldane's dilemma."
The discussion will now diverge into meaningless debate about a
non-existent phenomenon that is of no practical interest to modern
evolutionary biologists.
What is it with "Haldane's dilemma", anyways? I can understand why
anti-science idiots would want to use it a club to beat on evolution
but why would any real scientist pay attention?
Larry Moran
William Morse
> On Wed, 3 Mar 2004 16:51:14 +0000 (UTC),
> William Morse <wdm...@twcny.rr.com> wrote:
>> lam...@bioinfo.med.utoronto.ca (Larry Moran) wrote in
How major a role? Darwin's logic is fairly incontrovertible here - if
organisms produce more offspring than can survive (which they do), and if
there is heritable variation between those offspring (which there is)
then _if_ that variation results in a differential fitness (which appears
to be the crux of our disagreement) there _will be selection_ for the
morphological trait. Drift plays the major role at the molecular level
because most changes at that level _are_ selectively neutral. I can
change an alanine for a valine far from a binding site and selection
won't (at first) see it. But AFAIK drift hasn't made much of a dent in
the binding site of hemoglobin, to give only one obvious example.
Now while it is true that adaptationists are prone to conjuring up
explanations for observed morphological traits, that doesn't make those
explanations wrong, it just makes them untested. Ideally one would like
to alter the ear genes for African elephants, stick a bunch of small-
eared ones in an otherwise identical savanna environment, and see if they
survive as well as big eared ones, but even if we could perform the
experiment we would have to wait 20000 years for results, and even
postdocs might get a little antsy :-) Luckily for us mother nature has
performed some of these experiments for us. Pangolins, aardvarks,
anteaters, and echidnas are all mammals but otherwise quite unrelated -
except that they share the same ecological niche and share numerous
morphological traits. Take a good look sometime at pictures of the heads
of deer and kangaroos, which also only distantly share a common ancestor,
and use quite different mechanisms of locomotion (score one for
contingency!), but share a similar niche. A zoologist can look at the
teeth of an animal and tell you what it eats, can look at its skin and
tell you what climate it inhabits, can look at its eyes and tell you
whether it is predator or prey. So how are these morphological traits
_not_ adaptations?
The argument for drift is a much tougher row to hoe. You've got all the
tools of molecular biology that prove that drift occurs, but on a
morphological basis how do you prove a negative? And even if you do,
where is the glory? The adaptationist gets to come up with a great (if
unprovable) story, while the stochasticist is left with endless strings
of purines and pyrimidenes which mostly cannot (yet) be linked to
morphology and behavior.
(snip intro to this)
> So, is it possible that variation in skin color is due to selection in
> some parts of the world (Northern Europe) but drift elsewhere?
Certainly (although my argument is that "some parts of the world"
includes all of Europe, Africa, Asia and Australia) . Drift happens.
Selection happens. Calamity (aka shit) happens :-) If Arlin Stoltzfus
were still contributing to sbe he would be telling us that mutation
pressure happens. Evolution doesn't care which of the above is leading to
changes in gene frequencies. What I was trying to define with my "default
assumptions" was traits that were _primarily_ shaped by one or the other
- but there are no magic force fields that protect reproducing organisms
from any of the above effects.
(snip)
> (A minor quibble ... natural selection also has a major stochastic
> component. Most beneficial mutations are eliminated from the
> population. The best you can do is calulate the "probability" that a
> given allele will become fixed if you know the selection coefficient.)
Agreed. One of the reasons that zebra mussels have been able to spread so
rapidly in North American fresh waters is their ability to fix to a
substrate. This ability is common in mussels throughout the world, but
there are no native North American freshwater mussels that can do this.
Even I have difficulty in coming up with a Just So story to explain this
- it may well be due to "bad luck".
Yours,
Bill Morse
Tim Tyler
> This discussion involves an intricate interplay of several ideas
> 1. Species selection vs individual selection.
> 2. Selection vs drift
> 3. Long term vs short term.
>
> I hope I don't complicate things more by introducing a fourth issue - the
> dreaded Haldane's dilemma.
>
> My take on HD is that it points out that selection has a lot of work to
> do killing off the unfit, and only a finite time to do it. Selective
> deaths are a scarce resource [...]
Selective deaths /may/ be a scarse resource - so it's a good thing that
evolution can *also* produce adaptations via differential reproductive
success.
> and natural selection is unlikely to waste them on trivial things like
> optimizing the size of an elephant's ears - especially since there has
> only been a short time since African and Indian elephants diverged.
I'm pretty convinced that the large ears of African elephants exist
because they /are/ adaptive - primarily in the role of a thermoregulation
device. Asian elephants are significantly smaller *and* generally live
further north - in a cooler climate.
William Morse
> William Morse <wdm...@twcny.rr.com> wrote or quoted:
>
>> And I will further note that non-adaptive lock-ins are unlikely to
>> represent very many traits in old, widespread, morphologically stable
>> species, because such species are still subject to competition from
>> other species and have been for a long time. So they cannot afford
>> too much extra baggage.
>
> What if - after not very long - all their competition comes from other
> organisms with the same lock-in?
>
> I fully expect this is the case regarding a number of old, widespread
> and stable adaptations - such as the genetic code.
>
> I don't want to give too much weight to non-adaptive traits - but
> frozen accidents are certainly possible.
In another follow on this thread you mentioned that you might be accused
of arguing both sides of the point. I think that you _have_ been doing
that, and doing a right good job of it! One of Darwin's many good points
was his ability to see both sides of an argument - you also seem to have
this ability. I will now try to evince the same.
One of the key features of evolution is that it builds on previous
successes, vs. reinventing the wheel at every step. The downside of this
is that it is hard to go back. I seem to recall a recent article about a
clade of insects (dragonflies maybe?) reinventing flight after having
lost it. This was news because it almost never happens. So yes there will
be frozen accidents. Lavers in discussing elephant ears notes that
elephants don't sweat, perhaps because their ancestors lost the ability
during an aquatic phase (don't let Larry Moran know this!). Their big
ears may only be a "contingent" adaptation.
Yours,
Bill Morse
Tim Tyler
> Daisy World is a crock IMHO. Lovelock created an artificial model
> to illustrate the kinds of mechanisms that might lead to a Gaian
> homeostasis. But it would be just as easy to create a model
> of a world that doesn't exhibit homeostasis - that is actively unstable.
...if true, that would impact Lovelock's thesis not in the slightest.
He only suggested that the planet spends most of its time in a
homeostatic equilibrium orchestrated by living organisms.
The possibility of processes that drive the state away from equilibrium
is acknoledged - but they will only manifest themselves noticably during
times of instability - and dynamical systems are likely to spend most
of their times in stable states if these exist.
Indeed, the existence of such unstable processes simply echo the warnings
from the Gaia enthusiasts that the Earth will only stomach being pushed
so far before it flips into a new state - possibly one less habitable
by the forces causing the instability in the first place.
Also check out the properties of daisy world:
It suggests that white dasies reflect away more heat - and in hot times
will spread selfishly - and have the effect of cooling down the whole
planet.
Note that the local effect and the global one are both derived from
the same bit of physics: reflecting away heat cools you down.
If the model was changed - by wiping out the Sun and having the
heat source inside the planet - then black dasies will survives
better when it is too hot - since they will radiate heat away
from themselves better. However a planet covered with black
dasies will also cool down faster by radiating heat.
The fact that the model survives this sort of modification
suggests there is a general principle at work - /sometimes/
acting locally really does produce similar effects globally.
Some other examples where this might happen include reducing
levels of pollution, and dealing with resource shortages.
Jim Menegay
> JM:-
> Daisy World is a crock IMHO. Lovelock created an
> artificial model to illustrate the kinds of mechanisms that might lead
> to a Gaian homeostasis. But it would be just as easy to create a model
> of a world that doesn't exhibit homeostasis - that is actively unstable.
> >>
>
>
> I challenge you on that. Give an example.
>
OK. Lovelock's planet has two species - black daisies that absorb sunlight
warming the planet and white daisies that reflect sunlight cooling the
planet. My example will have the same two species.
In Lovelock's world, the black daisies prefer cool temperatures and the
white daisies prefer warm temperatures. Suppose the sun heats up for some
reason. Some of the black daisies die off and the white daisies occupy
their territory. This causes cooling, thus moderating the effect of the
solar fluctuation. Homeostasis.
In my world, which is equally likely, the black daisies prefer it hot, and
the white daisies prefer it cool. Now, when the sun heats up, the planet
heats up even more than a dead planet would. Instability.
> TH:-
> I think you will find that with out variations in the environment you won't
> have variants to select from, and more importantly there will be no cyclic
> predictable force for a chemistry system to adapt to - which is what life is
> IMO.
This confuses me. The whole point of Daisy World was to show that a living
planet suppresses variation in the environment. I would have expected that
you would have welcomed my opinion that this hypothetical suppression of
variation is a crock.
Tim Tyler
> Tim Tyler <t...@tt1lock.org> wrote in message news:<c28lqk$13co$1...@darwin.ediacara.org>...
> > Jim Menegay <jimme...@sbcglobal.net> wrote or quoted:
> > > Guy Hoelzer <hoe...@unr.edu> wrote in message news:<c1dfif$143o$1...@darwin.ediacara.org>...
> > > > IMHO, if Dawkins and his followers continue to ignore the
> > > > overwhelming evidence of adaptive "evolution" in complex
> > > > dynamical systems that seemingly lack the basic
> > > > ingredients for the process of natural selection (e.g.,
> > > > populations of reproducing agents), they will look
> > > > increasingly like closed-minded zealots as time goes on.
> > >
> > > This interests me, but puzzles me. What does "adaptive" mean in this
> > > context? I have a picture of a system (without reproducing parts)
> > > getting better at something - presumably something that is in its
> > > own best interests. But I don't see in what sense a dynamical
> > > system can be said to have interests.
> >
> > A brain is a complex adaptive system - it changes over time in a manner
> > that matches and reflects elements in its environment.
> >
> > You don't have to be able to self-reproduce to be able to adapt -
> > since there are other ways of adapting besides natural selection -
> > e.g. learning.
>
> But the brain is an evolved mechanism. Sure, systems that have been
> constructed by evolution or by intelligent design can be adaptive. The
> adaptiveness of such systems arises from their genesis, not from their
> complexity. [...]
Water poured onto a rocky landscape exhibits a "good fit" with the
contours of the landscape - and preserves it in the face of deformations
of that landscape.
For me, that's the essence of an adaptive system: it's exactly the
same sort of process that genes in organisms are performing on their
fitness landscapes.
> I thought that the issue was whether there is some sort of
> compulsion or tendency of complex systems to become adaptive.
Guy was saying that not all adaptive systems were the product of
evolution.
That seems a bit different to whether there's a tendency for
some class of systems to come to exhibit adaptive behaviour.
John Edser
> >> Two points ...
> >>
> >> 1. Genetic diversity cannot be an adaptation since this requires a form
> >> of group selection that has been thoroughly discredited. If a
species
> >> accidently possesses more diversity then it will be the lucky
survivor
> >> when the environment changes. This is more like evolution by chance
> >> that real adaptation.
> > Two points ...
> > 1. Inbreeding depression is a form of lack of genetic diversity that can
> > increase the chance that a population goes extinct. This will generally
> > work at low effective population sizes.
> This is correct but that's not the point. The point is whether you can
> *select* for diversity within a population based on the assumption that
> it will become useful at some future date.
JM:-
This discussion involves an intricate interplay of several ideas
1. Species selection vs individual selection.
2. Selection vs drift
3. Long term vs short term.
JE:-
Why did you exclude "Organism Fitness Mutualism"
(OFM)?
The main reason as to why "you can
*select* for diversity within a population
based on the assumption that
it will become useful at some future date"
is because it increases _mutualised_ fitness.
When forms make associations that benefit
each form in absolute fitness but do not
necessarily benefit them equally, then
selection must increase the diversity between
mutualised forms. This is because there
is little point forming an OFM association
when they are mostly the same. OFM is a form of
unconscious trade. It is best to trade with
those who do things better and differently.
IMO, the most obvious example of OFM selecting
for increased diversity is in the evolution of
sex. Gene centrists have great difficulty in
attempting to explain the evolution of non hermaphrodite
sex because the males do not give birth
resulting is a 50% _gene centric_ loss. Of course
if you only use Darwinian fitness this "loss" is only
a possibility, i.e. it is not measured as an actual
loss. In Darwinian fitness terms a potential
loss can only be measured by a reduction of _fertile_
forms reproduced. For sex to evolve via Darwinian
evolution and Darwinian fitness any potential
loss must have resolved itself to become, an absolute
parental fitness GAIN.
The more intense OFM becomes, the more selective
pressure that is applied to each, separate,
Darwinian entity to increase heritable diversity for
each entity within each OFM group. I stress:
THIS IS NOT GROUP SELECTION.
L. Moran et al, do not understand how group selection
differs from Darwinian selection. This is proven when
b within Hamilton's rule was not understood by them
to be group selective in the classical sense of the
word.
JM:-
I hope I don't complicate things more by introducing a fourth issue - the
dreaded Haldane's dilemma.
My take on HD is that it points out that selection has a lot of work to
do killing off the unfit, and only a finite time to do it. Selective
deaths are a scarce resource, and natural selection is unlikely to waste
them on trivial things like optimizing the size of an elephant's ears -
especially since there has only been a short time since African and Indian
elephants diverged.
That is, I am taking HD as an argument against extreme adaptationism.
But HD is also applicable to the question of long term vs short term.
If a trait is disadvantageous in the short term, but advantageous in the
long term, should we expect the trait to persist in a population? Sure,
why not, suggests HD, as long as the short term disadvantage is small in
comparison with the other issues that selection has to deal with.
That is, I am suggesting here that the orthodox belief in the idea that
the short term always trumps the long term is probably wrong.
JE:-
You should go back in sbe archives and read the long
tortuous discussions between Walter ReMine and Prof.
Felsenstein on Haldane's Dilemma. Haldane is the source
of two major Neo Darwinistic errors re: model _misuse_:
1) Haldane's Dilemma
2) His discussion of OFA that preceded
Hamilton's views on the same subject.
Haldane's Dilemma:
The discussion was based on Haldane's
simplified model that predicted that not enough
time existed to allow man and chimp to evolve
from a common ancestor. Haldane based his calculations
on an _inflated_ size re: the human genome. His
assumption of the probable size of the human genome
was many more times bigger than it was actually
proven to be. Since the discovery of the relatively
small size of the human genome, the "Haldane's Dilemma"
story has been reduced to just a waste caused by crossing
gene centric bridges before you come to
them. Given the actual size of the human genome
and the tiny differences that exist between it
and the chimp genome, more than enough time has
passed to evolve chimps and men from a common
ancestor, using Haldane's assumptions. Thus it
just is red faces all round on this issue.
ReMine (a creationist) who had written a large
book on the subject and was attempting to hit
evolutionary theory over the head with
Haldane's dilemma, refused to admit that he
was wrong. Prof. Felsenstein refused to admit
that the dilemma was unreal to start with ,
i.e. was a just a waste of time and resources
caused by the _misuse_ of Haldane's oversimplified
view of nature.
The most important issue re: Haldane's
Dilemma remains NON DISCUSSED. The dilemma
was wrong because Haldane's inflated size for
the human genome, was wrong. Why did gene centric
Neo Darwinists consider such a huge genome
a necessity? Simply because they needed
such a huge genome if just additive epistasis
(which just means no epistasis at all!) was
allowed as "heritable". Fisher's model deleted
all gene fitness epistasis. It redefined
"non additive" epistasis as "inherited" but
"non heritable" and thus "non selectable".
We are stuck with Fisher to this very day.
The fact is, the failure of Haldane's dilemma
points to Fisher's failure re: what is and what
is not validly regarded as "heritable". If non additive
information can be "heritable" and thus "selectable"
then the human genome can be compressed like a zip
file.
OFA:
In the now famous pub discussion, Haldane
did not include any value for cmax. This
discussion pre-empted Hamilton by many years.
Hamilton made the same mistake of not including
a maximal value for c within his famous rule.
In both cases, only relative fitness was included
allowing for totally erroneous arguments to
occupy evolutionary theory for over 50 years
re: the evolution of OFA within nature.
OFA could not be supported by Hamilton's rule
because OFA can only be diagnosed from OFM
using the sign of c. Within Hamilton's rule.
the sign of c remains _arbitrary_ .
Thus at all times OFM OR OFA can be validly
supposed to be operating within
Hamilton's rule. Thus the rule was entirely
misused to support OFA within nature after
group selection failed to do so. To this day,
no theory of nature has been proposed that
supports OFA. Gene centric
Neo Darwinists have had to resort to redefining
nature as just their simplified model view while wheeling
in Post Modern epistemology to justify such nonsense.
Respectfully,
John Edser
Independent Researcher
PO Box 266
Church Pt
NSW 2105
Australia