Natural selection vs mutation - in the news
Tim Tyler
http://www.sciencedaily.com/releases/2008/01/080118134531.htm
Evolution Is Deterministic, Not Random, Biologists Conclude From
Multi-species Study
http://www.sciencedaily.com/releases/2007/11/071119123929.htm
Of course, these studies look at traits, not gene sequences.
--
__________
|im |yler http://timtyler.org/ t...@tt1lock.org Remove lock to reply.
Ron O
> New Findings Confirm Darwin's Theory: Evolution Not Random
>
> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
Sounds like muddled gobblety goop.
QUOTE:
When the researchers measured changes in 40 defined characteristics of
the nematodes' sexual organs (including cell division patterns and the
formation of specific cells), they found that most were uniform in
direction, with the main mechanism for the development favoring a
natural selection of successful traits, the researchers said.
"Since random development would not create such unifying trends, we
concluded that the observed development was deterministic, not
random," said Professor Benjamin Podbilewicz from the Technion Faculty
of Biology.
The findings, which constitute a significant milestone in establishing
and reaffirming the mechanism of Darwin's theory, will help in
understanding how evolution works in all living creatures, said
Podbilewicz.
END QUOTE:
These guys either rediscovered canalization, or they don't understand
that biological evolution has to build on what came before. Where
else are beneficial phenotypes going to come from? The negative, not
so beneficial, phenotypes have to come from the same starting
phenotypes. Does anyone not get that? Something probably got lost in
translation.
Ron Okimoto
Tim Tyler
> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>> New Findings Confirm Darwin's Theory: Evolution Not Random
>>
>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
> Sounds like muddled gobblety goop.
>
> QUOTE:
> When the researchers measured changes in 40 defined characteristics of
> the nematodes' sexual organs (including cell division patterns and the
> formation of specific cells), they found that most were uniform in
> direction, with the main mechanism for the development favoring a
> natural selection of successful traits, the researchers said.
>
> "Since random development would not create such unifying trends, we
> concluded that the observed development was deterministic, not
> random," said Professor Benjamin Podbilewicz from the Technion Faculty
> of Biology.
>
> The findings, which constitute a significant milestone in establishing
> and reaffirming the mechanism of Darwin's theory, will help in
> understanding how evolution works in all living creatures, said
> Podbilewicz.
> END QUOTE:
>
> These guys either rediscovered canalization, or they don't understand
> that biological evolution has to build on what came before. Where
> else are beneficial phenotypes going to come from? [...]
You mean if not from random mutation? I don't think they
are denying that random mutations exist, merely suggesting
that they do not determine the direction of evolution in
the cases they studied.
Rather like the way brownian motion does not determine
the direction of modern aircraft.
Sure, if you take away the air, the plane falls out of
the sky - but the molecular impacts don't seem to
determine the plane's destination, whereas the travel
schedule back at air traffic control reveals all.
Lorentz
> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>
> > New Findings Confirm Darwin's Theory: Evolution Not Random
>
> > http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
> Sounds like muddled gobblety goop.
investigators got Lamarkian and Darwinian evolution exactly backwards.
I thought Lamarkian evolution is where "useful" traits get
preferentially inherited, and that in Darwinian evolution traits
usually get inherited without any preference to "useful traits." The
article is seemed to be claiming that Darwinian evolution is the model
where "useful" traits get inherited.
However, it seems on rereading the articles that the writer
doesn't have a clear idea of what Darwinian evolution is. The
existence of a directional trend does not disprove the idea of
"random" inheritance. The long term trend could be directional due to
natural selection, it is only the generation to generation variation
that has to be "random."
For example, they claim that the number of cell divisions
consistently decreased in time even in different lineages. However,
the data they have isn't resolved on a generation by generation basis.
So maybe there were nematodes individuals who showed an increase in
cell divisions relative to their parents. They got selected out. They
died. Averaging the number of cell divisions per vulva in each
generation, a trend shows up where the average number of cell
divisions decreases with the number of generations. That has nothing
to do with whether the inheritance is deterministic or not. What are
these guys talking about?
Ron O
> Ron O wrote:
> > On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >> New Findings Confirm Darwin's Theory: Evolution Not Random
>
> >> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
> > Sounds like muddled gobblety goop.
>
> > QUOTE:
> > When the researchers measured changes in 40 defined characteristics of
> > the nematodes' sexual organs (including cell division patterns and the
> > formation of specific cells), they found that most were uniform in
> > direction, with the main mechanism for the development favoring a
> > natural selection of successful traits, the researchers said.
>
> > "Since random development would not create such unifying trends, we
> > concluded that the observed development was deterministic, not
> > random," said Professor Benjamin Podbilewicz from the Technion Faculty
> > of Biology.
>
> > The findings, which constitute a significant milestone in establishing
> > and reaffirming the mechanism of Darwin's theory, will help in
> > understanding how evolution works in all living creatures, said
> > Podbilewicz.
> > END QUOTE:
>
> > These guys either rediscovered canalization, or they don't understand
> > that biological evolution has to build on what came before. Where
>
> You mean if not from random mutation? I don't think they
> are denying that random mutations exist, merely suggesting
> that they do not determine the direction of evolution in
> the cases they studied.
>
> Rather like the way brownian motion does not determine
> the direction of modern aircraft.
>
> Sure, if you take away the air, the plane falls out of
> the sky - but the molecular impacts don't seem to
> determine the plane's destination, whereas the travel
> schedule back at air traffic control reveals all.
> __________
> |im |yler http://timtyler.org/ t...@tt1lock.org Remove lock to reply.- Hide quoted text -
>
> - Show quoted text -
You are just describing the fact that biological evolution has to
build on what it has at the moment. No matter what new mutations
occur they have to interact with the current genetics and phenotype of
the organism. This means that we don't expect Mammals to sprout
feathered wings on their shoulders. No big surprise. Look up
canalization. This is absolutely no surprise to evolutionary
biologists. Why would these guys expect evolution to be directionless
when it obviously has a starting point to work from? Your options of
useful mutations is limited. Just think for a moment. Would the same
mutations in the same genes have to have the same effect in birds as
in mammals? The answer is no. A mutation that stiffened the wing
feathers of a bird might just make the fur coarser in mammals. One
might benefit flight in birds and the same mutation in mammals might
do something about heat exchange.
Ron Okimoto
Tim Tyler
> On Jan 21, 10:52 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>> Ron O wrote:
>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>>> Sounds like muddled gobblety goop.
[...]
>>> These guys either rediscovered canalization, or they don't understand
>>> that biological evolution has to build on what came before. Where
>>> else are beneficial phenotypes going to come from? [...]
>>
>> You mean if not from random mutation? I don't think they
>> are denying that random mutations exist, merely suggesting
>> that they do not determine the direction of evolution in
>> the cases they studied.
>>
>> Rather like the way brownian motion does not determine
>> the direction of modern aircraft. [...]
>
> You are just describing the fact that biological evolution has to
> build on what it has at the moment. No matter what new mutations
> occur they have to interact with the current genetics and phenotype of
> the organism. This means that we don't expect Mammals to sprout
> feathered wings on their shoulders. No big surprise. Look up
> canalization. This is absolutely no surprise to evolutionary
> biologists. Why would these guys expect evolution to be directionless
> when it obviously has a starting point to work from? Your options of
> useful mutations is limited. Just think for a moment. Would the same
> mutations in the same genes have to have the same effect in birds as
> in mammals? The answer is no. A mutation that stiffened the wing
> feathers of a bird might just make the fur coarser in mammals. One
> might benefit flight in birds and the same mutation in mammals might
> do something about heat exchange.
This thread is not about canalization.
There is a longstanding debate in biology about the significance
of the role of chance in forming observed biological structures.
E.g. see "Chance and Necessity" by Jacques Monod, as reviewed here:
http://dannyreviews.com/h/Chance_and_Necessity.html
To summarise:
We have examples of contingency in biology - e.g.
as far as anyone knows, the liver could equally
well have been on the left hand side of the body -
and only accidents among our ancestors placed it
on the right.
We also have examples of chance not making much difference,
e.g. see:
http://en.wikipedia.org/wiki/Convergent_evolution
....which illustrates organisms converging on the
same adaptation, *despite* differing starting points.
So: the issue arises of which /kind/ of explanation to invoke
when faced with the observed features of organisms:
Chance? Or necessity?
The point of this thread is that it reports on experiments
which bear on that issue.
Arlin
>
> > New Findings Confirm Darwin's Theory: Evolution Not Random
>
> > http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
> Sounds like muddled gobblety goop.
Yes, the analysis is flawed, particularly by the use of the concept of
"deterministic". They may be able to argue for a statistical bias in
some cases, but "deteminism" is not the right word. Regardless, it
might help to get the issues straight here on sbe. Kiontke, et al.
present an impressive set of systematic data that deserves careful
scrutiny. The data are on the divergence of a large number of
phenotypic characters (relating to worm vulval morphology and
development) for a large number of species. We desperately need
systematic data sets just like this to address "evo-devo" questions.
The first issue to address is whether the results of their
phylogenetic reconstructions eliminate an unbiased random walk model
for the characters studied. The second question is, in the case of
biased evolution of a character, what is the cause of the bias. They
consider two possible causes, directional selection and "developmental
constraint".
My initial reading of the paper is that the first issue is not
addressed properly. If a character changes 4 times in one direction,
and once in the other direction, this is not a statistically
significant result, i.e., it does not eliminate the null hypothesis of
an unbiased random walk in which the chance of a change in one
direction is the same as in the other. There are some impressive
examples of bias, but most of the characters do not seem to change
much. In my opinion, if one looks closely at the results in Table 1,
the authors conclusion on this issue is tenuous at best.
On the second issue, contrary to what some people here on sbe are
suggesting, the authors do not report any firm conclusion. They
suggest that the biases might be due to selection, or to what they
call "selection-independent" constraints (in this regard, they cite
authors such as Arthur or Yampolsky and Stoltzfus who do not really
agree on the relevance of their conception of "constraint"). They do
not claim to be able to distinguish these two competing
explanations. The interesting question to ask, in this case, is how
one might use further experiments and analysis to distinguish these
explanations.
Arlin
Alberto Gómez Corona
Evolution is the fact of reality,
Natural selection is the key part of the scientific theory that
explain this fact of reality without invocating either religious or
naturalistic magic steps and
Mutation is one of variation mechanisms that permits a selection among
the varieties generated.
Thus, neither "natural selection vs mutation" or "mutation theory"
or "Evolution theory" makes any sense
Ron O
> >> Ron O wrote:
> >>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >>>> New Findings Confirm Darwin's Theory: Evolution Not Random
> >>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
> >>> Sounds like muddled gobblety goop.
>
>
>
>
>
>
>
>
> >>> These guys either rediscovered canalization, or they don't understand
> >>> that biological evolution has to build on what came before. Where
> __________
> |im |yler http://timtyler.org/ t...@tt1lock.org Remove lock to reply.-
Nope, still canalization, just think about it. You only have a
limited number of avenues to take from a given starting point.
Similar selective conditions will only be able to exploit those
limited ways to go. No mystery.
Now they would really have something if they claimed that they had
found fish that evolved lungs, warm blooded, placental live birth, and
a blow hole at the top of their heads, and moved into the whales
niche.
Ron Okimoto
Tim Tyler
> On Jan 22, 10:29 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>> Ron O wrote:
>>> On Jan 21, 10:52 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>> Ron O wrote:
>>>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
>>>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
[...]
>>>>> These guys either rediscovered canalization, or they don't understand
>>>>> that biological evolution has to build on what came before. Where
>>>>> else are beneficial phenotypes going to come from? [...]
>>>> You mean if not from random mutation? I don't think they
>>>> are denying that random mutations exist, merely suggesting
>>>> that they do not determine the direction of evolution in
>>>> the cases they studied.
>>>> Rather like the way brownian motion does not determine
>>>> the direction of modern aircraft. [...]
>>> You are just describing the fact that biological evolution has to
>>> build on what it has at the moment. [...]
>> This thread is not about canalization.
>>
>> There is a longstanding debate in biology about the significance
>> of the role of chance in forming observed biological structures.
>> E.g. see "Chance and Necessity" by Jacques Monod, as reviewed here:
>>
>> http://dannyreviews.com/h/Chance_and_Necessity.html
>>
>> To summarise: [...]
>> So: the issue arises of which /kind/ of explanation to invoke
>> when faced with the observed features of organisms:
>> Chance? Or necessity?
>>
>> The point of this thread is that it reports on experiments
>> which bear on that issue.
>
> Nope, still canalization, just think about it. You only have a
> limited number of avenues to take from a given starting point.
> Similar selective conditions will only be able to exploit those
> limited ways to go. No mystery.
I /thought/ I had already replied clearly :-|
To use your terminology, from any given starting point
there will be a limited number of directions in which
an organism can develop - due to factors such as
developmental constraints.
However, there may /still/ be choices - about which
evolutionary path species will taken.
The "chance" perspective suggests choices are common -
and that selection plays a relatively minor role
in determining the direction taken - instead,
chance is responsible.
The "necessity" perspective suggests choices are
either rare or that they lead to the same
endpoint - and so don't make much difference
in the long term.
Obviously some combination of these perspectives
is correct, but their relative frequency,
weighting or significance is not obvious -
and the point of this thread is that it
reports on experiments which bear on this issue.
I am puzzeled about why I am having to explain
this repeatedly.
Aren't sci.bio.evolution posters /supposed/ to
understand what the "Chance and Necessity"
issue is about?
Ron O
> Ron O wrote:
> > On Jan 22, 10:29 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >> Ron O wrote:
> >>>> Ron O wrote:
> >>>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >>>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
> >>>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
>
>
>
>
>
> >>>>> These guys either rediscovered canalization, or they don't understand
> >>>>> that biological evolution has to build on what came before. Where
This is the important point. "May/still/be choices" is what you have
to demonstrate. You have to take the examples that you are using and
demonstrate that there were choices, how many, and how varied would
their end points be given the basic genetics and phenotype of the
organism and the environment that it finds itself? Do you have such a
paper? Why couldn't canalization explain any such examples put
forward. It will until the researchers can determine that there were
other paths that would have made a significant difference in the
outcome, and that these other paths had an equal chance of being
taken, or at least enough of a chance of being taken to have been
observed more often than they are observed. There really are not a
large number of possibilities that have an equal chance of occurring.
In any given case there are probably no equally probable paths to
take. Wouldn't you agree with that last statement? How equally
probable would two choices be for either to be taken a significant
number of times? I don't know.
Ron Okimoto
>
> The "chance" perspective suggests choices are common -
> and that selection plays a relatively minor role
> in determining the direction taken - instead,
> chance is responsible.
>
> The "necessity" perspective suggests choices are
> either rare or that they lead to the same
> endpoint - and so don't make much difference
> in the long term.
>
> Obviously some combination of these perspectives
> is correct, but their relative frequency,
> weighting or significance is not obvious -
> and the point of this thread is that it
> reports on experiments which bear on this issue.
>
> I am puzzeled about why I am having to explain
> this repeatedly.
>
> Aren't sci.bio.evolution posters /supposed/ to
> understand what the "Chance and Necessity"
> issue is about?
> --
> __________
John W Edser
>> The "chance" perspective suggests choices are common -
>> and that selection plays a relatively minor role
>> in determining the direction taken - instead,
>> chance is responsible.
>> The "necessity" perspective suggests choices are
>> either rare or that they lead to the same
>> endpoint - and so don't make much difference
>> in the long term.
JE:-
Chance provides heritable change which can only limit what the Darwinian non
random process of natural selection may select. Chance can indeed determine
which way a heritable pathway may take. An example would be which way around
the pre-retinal cells within a primordial eye happened to be facing.
However, it should be self evident that this _complex phenotype_ can only
remain a heritable trait if it is coded by genes at many different loci in
the same genome, acting in concert. IOW this 50/50 chance switching event
was not just the action of an isolated random process because it was and
remains, critically incorporated within a non random mechanism. In the
vertebrates and most probably only by chance, the primordial retinal cells
were facing the wrong way; however the invertebrates were luckier. IOW
epistatic (non additive in fitness) _heritable gene complexes_ act like
single mutated genes which can switch more complex phenotypes. Note that non
additive epistasis can employ a high or low gearing to preserve a phenotype
against change (canalization) or accelerate the rate of heritable change of
a different phenotype (assimilation) within the same genome accelerating the
rate of evolution. The invertebrate eye of an octopus is analogous to that
of a mammal. Analogies are common testifying to the power of non random
evolution over supposed, incorrect propositions of independent acts of
random evolution (heritable mutation and genetic drift). My point: random
processes work hand in hand with the non random process of natural selection
because they remain 100% incorporated within the one, same falsifiable
theory of evolution. Attempting to separate them by deploying mathematics
can only provide biological absurdities.
> I am puzzeled about why I am having to explain
> this repeatedly.
> Aren't sci.bio.evolution posters /supposed/ to
> understand what the "Chance and Necessity"
> issue is about?
JE:-
Random processes were and remain corporated with non random natural
selection within just the one, same falsifiable theory of evolution. This is
what "Chance and Necessity" is all about. Attempts by mathematicians to
separate "chance" from the "necessity" of non random selection events within
the one, same falsifiable theory represents a critical error.
Regards,
John Edser
Independent Researcher
J.A.Legris
> Ron O wrote:
> > On Jan 22, 10:29 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >> Ron O wrote:
> >>>> Ron O wrote:
> >>>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >>>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
> >>>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
>
>
>
> >>>>> These guys either rediscovered canalization, or they don't understand
> >>>>> that biological evolution has to build on what came before. Where
> and that selection plays a relatively minor role
> in determining the direction taken - instead,
> chance is responsible.
>
> The "necessity" perspective suggests choices are
> either rare or that they lead to the same
> endpoint - and so don't make much difference
> in the long term.
>
> is correct, but their relative frequency,
> weighting or significance is not obvious -
> and the point of this thread is that it
> reports on experiments which bear on this issue.
>
> this repeatedly.
>
> Aren't sci.bio.evolution posters /supposed/ to
> understand what the "Chance and Necessity"
> issue is about?
>
Perhaps not. But it might be a good idea if everyone read the article
in question (e-mail me if you want to see "my" copy):
Kiontke et al.
Trends, Stasis, and Drift in the Evolution of Nematode Vulva
Development.
Current Biology 17, 1925-1937, November 20, 2007
--
Joe
Tim Tyler
> On Jan 26, 12:18 am, Tim Tyler <seemy...@cyberspace.org> wrote:
>> Ron O wrote:
>>> On Jan 22, 10:29 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>> Ron O wrote:
>>>>> On Jan 21, 10:52 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>>>> Ron O wrote:
>>>>>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
>>>>>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
>>>>>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
[...]
>>>>>>> These guys either rediscovered canalization, or they don't understand
>>>>>>> that biological evolution has to build on what came before. Where
>>>>>>> else are beneficial phenotypes going to come from? [...]
>>>>> You are just describing the fact that biological evolution has to
I /did/ give an example of chance:
``We have examples of contingency in biology - e.g.
as far as anyone knows, the liver could equally
well have been on the left hand side of the body -
and only accidents among our ancestors placed it
on the right.''
This is not canalization - since the resulting
phenotypes are different.
Another source of such symmetry breaking which is /not/
so trivial arises through divergent selection. There,
it doesn't matter much who gets which trait /provided/
different species get different traits, and either
they don't want to mate, or can't mate with their
more distant cousins.
Sexual selection seems to be another source of randomness,
since fashion is a notoriously unpredictable subject.
The frequency and significance of such chance events is what
is discussed in the paper the news article reported on:
Trends, Stasis, and Drift in the Evolution of Nematode Vulva Development
http://download.current-biology.com/pdfs/0960-9822/PIIS0960982207021938.pdf
> In any given case there are probably no equally probable paths to
> take. Wouldn't you agree with that last statement?
In the example of liver location, from a suitably distant ancestor -
e.g. the LUCA - my estimate of the chances would be between 49% and
51%. As close to 50-50 as makes no practical difference.
Rereading this thread, I /do/ see the link to genetic canalisation;
my aplogies for denying such a connection.
John W Edser
> ``We have examples of contingency in biology - e.g.
> as far as anyone knows, the liver could equally
> well have been on the left hand side of the body -
> and only accidents among our ancestors placed it
> on the right.''
>
> This is not canalization - since the resulting
> phenotypes are different.
JE:-
Incorrect. It was indeed canalization because both of these 100% randomly
switched phenotypes had to be epistatically (non additively) coded just to
remain heritable (making nonsense out of Fisher's dictate that non additive
epistasis cannot be heritable). If this was not the case they would be
randomly switching backwards and forwards to this very day. Your attempt to
focus attention on just the random aspect of the example belies the
biological fact that a random base rate of mutation incorporated within non
random natural selection remains the basis of a falsifiable Darwinian theory
and not either as heuristically separate theories of evolution in their own
right. Only ignorant mathematicians attempt to separate them into just
futile competing camps.
Ron O
> Ron O wrote:
> > On Jan 26, 12:18 am, Tim Tyler <seemy...@cyberspace.org> wrote:
> >> Ron O wrote:
> >>> On Jan 22, 10:29 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >>>> Ron O wrote:
> >>>>>> Ron O wrote:
> >>>>>>> On Jan 19, 4:51 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
> >>>>>>>> New Findings Confirm Darwin's Theory: Evolution Not Random
> >>>>>>>> http://www.sciencedaily.com/releases/2008/01/080118134531.htm
>
>
>
>
>
>
> >>>>>>> These guys either rediscovered canalization, or they don't understand
> >>>>>>> that biological evolution has to build on what came before. Where
> as far as anyone knows, the liver could equally
> well have been on the left hand side of the body -
> and only accidents among our ancestors placed it
> on the right.''
>
> This is not canalization - since the resulting
> phenotypes are different.
This is not a good example. How many times did the liver evolve and
it likely occurs on the other side in some cases. How do you know
that it isn't canalization that only one liver (who cares on what
side) evolved due to developmental constraints imposed by
development? Symetry with two livers might have been expected, but
due to developmental constraints in evolving other single organs what
would make the liver different?
>
> Another source of such symmetry breaking which is /not/
> so trivial arises through divergent selection. There,
> it doesn't matter much who gets which trait /provided/
> different species get different traits, and either
> they don't want to mate, or can't mate with their
> more distant cousins.
This could also be canalization just think. at any given point if you
diverge from one phenotype, how many ways can you diverge? Is there a
more likely path due to where you are starting in either direction? I
would think so. You have to determine how many possible paths and how
likely they are to be taken before you can rule out canalization as an
explanation for similar paths taken from a single point.
>
> Sexual selection seems to be another source of randomness,
> since fashion is a notoriously unpredictable subject.
What gets sexually selected, doesn't it depend on what is already
present?
Don't you have to have eye spots already before you select for more or
less of them? How many ways can you shorten or lenghten a tail?
Select for larger or smaller head ornaments? Not only that, but just
look at the birds of paradise where is the similar paths taken by
sexual selection in that case? It looks like females picked up on a
wide variety of differences to select on. Sure the same feather
tracks got changed, but in different colors and in various ways.
There was a limitation how the ornaments changed, but the various
species still changed them in different ways. You might claim that
there was a general trend to elongate the coverts or some other
feather tract, but how many ways are you going to change the growth of
the coverts to make something unusual? What similarities in this
variety can't have something to do with canalization?
>
> The frequency and significance of such chance events is what
> is discussed in the paper the news article reported on:
>
> Trends, Stasis, and Drift in the Evolution of Nematode Vulva Development
>
> http://download.current-biology.com/pdfs/0960-9822/PIIS09609822070219...
If you look at nematodes they have a very limited character set to
change. They have a fairly simple basic body plan that has been
retained for about as long as anything else except possibly the flat
worm body plan. Beats me how many ways you can change the vulva
development, but there has been stablizing selection for the basic
body plan for quite a long time. The sexual parts are about the only
thing that you can use to tell some species apart. I don't know if I
would bet the farm on generalizing from nematode evolution.
>
> > In any given case there are probably no equally probable paths to
> > take. Wouldn't you agree with that last statement?
>
> In the example of liver location, from a suitably distant ancestor -
> e.g. the LUCA - my estimate of the chances would be between 49% and
> 51%. As close to 50-50 as makes no practical difference.
How many times did the liver evolve? What does it tell you about
paths usually taken more often than chance?
Ron Okimoto
>
> Rereading this thread, I /do/ see the link to genetic canalisation;
> my aplogies for denying such a connection.
> --
> __________