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Zebra stripes evolved to keep biting flies at bay
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Metspitzer
Feb 10, 2012, 6:33:07 PM2/10/12
to
Why zebras evolved their characteristic black-and-white stripes has
been the subject of decades of debate among scientists.
Now researchers from Hungary and Sweden claim to have solved the
mystery.
The stripes, they say, came about to keep away blood-sucking flies.
They report in the Journal of Experimental Biology that this pattern
of narrow stripes makes zebras "unattractive" to the flies.
They key to this effect is in how the striped patterns reflect light.
Continue reading the main story
"We started off studying horses with black, brown or white coats,"
explained Susanne Akesson from Lund University, a member of the
international research team that carried out the study.
"We found that in the black and brown horses, we get horizontally
polarised light." This effect made the dark-coloured horses very
attractive to flies.
It means that the light that bounces off the horse's dark coat - and
travels in waves to the eyes of a hungry fly - moves along a
horizontal plane, like a snake slithering along with its body flat to
the floor.
Dr Akesson and her colleagues found that horseflies, or tabanids, were
very attracted by these "flat" waves of light.
"From a white coat, you get unpolarised light [reflected]," she
explained. Unpolarised light waves travel along any and every plane,
and are much less attractive to flies. As a result, white-coated
horses are much less troubled by horseflies than their dark-coloured
relatives.
Having discovered the flies' preference for dark coats, the team then
became interested in zebras. They wanted to know what kind of light
would bounce off the striped body of a zebra, and how this would
affect the biting flies that are a horse's most irritating enemy.
"We created an experimental set-up where we painted the different
patterns onto boards," Dr Akesson told BBC Nature.
http://www.bbc.co.uk/nature/16944753
been the subject of decades of debate among scientists.
Now researchers from Hungary and Sweden claim to have solved the
mystery.
The stripes, they say, came about to keep away blood-sucking flies.
They report in the Journal of Experimental Biology that this pattern
of narrow stripes makes zebras "unattractive" to the flies.
They key to this effect is in how the striped patterns reflect light.
Continue reading the main story
"We started off studying horses with black, brown or white coats,"
explained Susanne Akesson from Lund University, a member of the
international research team that carried out the study.
"We found that in the black and brown horses, we get horizontally
polarised light." This effect made the dark-coloured horses very
attractive to flies.
It means that the light that bounces off the horse's dark coat - and
travels in waves to the eyes of a hungry fly - moves along a
horizontal plane, like a snake slithering along with its body flat to
the floor.
Dr Akesson and her colleagues found that horseflies, or tabanids, were
very attracted by these "flat" waves of light.
"From a white coat, you get unpolarised light [reflected]," she
explained. Unpolarised light waves travel along any and every plane,
and are much less attractive to flies. As a result, white-coated
horses are much less troubled by horseflies than their dark-coloured
relatives.
Having discovered the flies' preference for dark coats, the team then
became interested in zebras. They wanted to know what kind of light
would bounce off the striped body of a zebra, and how this would
affect the biting flies that are a horse's most irritating enemy.
"We created an experimental set-up where we painted the different
patterns onto boards," Dr Akesson told BBC Nature.
http://www.bbc.co.uk/nature/16944753
chris thompson
Feb 10, 2012, 6:48:01 PM2/10/12
to
Dipterans were attracted to differing light patterns, and if that
matched up with the different widths of stripe patterns on the
different species of zebras.
Chris
Richard Norman
Feb 10, 2012, 8:46:34 PM2/10/12
to
behavioral studies in the actual paper show that the zebra striped
pattern is less attactive to horse flies, Tabanids, than either solid
black or white. The abstract to the real paper doesn't emphasize the
polarized light aspect and the title is about brightness/polarization
patterns. I haven't yet checked the text to see just what role
polarized light plays other than as a possibility.
The paper itself is
Polarotactic tabanids find striped patterns with brightness and/or
polarization modulation least attractive: an advantage of zebra
stripes
A Egri et al.
J Exp Bio l215, 736-745 (2012)
http://jeb.biologists.org/content/215/5/736
To be specific, the abstract claims:
"Here, we demonstrate that a zebra-striped horse model attracts far
fewer horseflies (tabanids) than either homogeneous black, brown, grey
or white equivalents...Besides brightness, one of the likely
mechanisms underlying this protection is the polarization of reflected
light from the host animal. We show that the attractiveness of striped
patterns to tabanids is also reduced if only polarization modulations
(parallel stripes with alternating orthogonal directions of
polarization) occur in horizontal or vertical homogeneous grey
surfaces."
Don Cates
Feb 11, 2012, 12:31:15 AM2/11/12
to
attention of these flies and zebra reproductive success before claiming
any evolutionary connection?
--
--
Don Cates ("he's a cunning rascal" PN)
Richard Norman
Feb 11, 2012, 1:06:08 AM2/11/12
to
On Fri, 10 Feb 2012 23:31:15 -0600, Don Cates <caHOR...@mts.net>
wrote:
Horse flies are truly horrible blood sucking pests. Anyone aquainted
with their bites or has seen animals trying to escape them doesn't
doubt that protection from their attack is a Good Thing. Animals
attacked by a large number of flies are often severely weakened and
can die from blood loss, not to mention the diseases spread by the
flies.
In thinking about the effect of stripes, it occurs to me that the
flies (actually only the females bite and suck blood) might use a
search pattern to find prey locating very large dark objects
preferentially or alternatively large white objects. Objects that are
variegated or striped might not be seen as "large objects". The
pattern breaks up the animal's outline so a predator gets confused
about what is is looking at. That is an example of disruptive
coloration, usually the explanation for zebra stripes in confusing
predators like the big cats or hyenas. When zebras run together as a
herd it is very difficult to tell just where one particular animal
begins or ends. For insects, this effect would work equally
effectively for intensity (black vs white) and polarization (polarized
vs not) variation in the object viewed.
wrote:
with their bites or has seen animals trying to escape them doesn't
doubt that protection from their attack is a Good Thing. Animals
attacked by a large number of flies are often severely weakened and
can die from blood loss, not to mention the diseases spread by the
flies.
In thinking about the effect of stripes, it occurs to me that the
flies (actually only the females bite and suck blood) might use a
search pattern to find prey locating very large dark objects
preferentially or alternatively large white objects. Objects that are
variegated or striped might not be seen as "large objects". The
pattern breaks up the animal's outline so a predator gets confused
about what is is looking at. That is an example of disruptive
coloration, usually the explanation for zebra stripes in confusing
predators like the big cats or hyenas. When zebras run together as a
herd it is very difficult to tell just where one particular animal
begins or ends. For insects, this effect would work equally
effectively for intensity (black vs white) and polarization (polarized
vs not) variation in the object viewed.
jillery
Feb 11, 2012, 3:45:30 AM2/11/12
to
was focused on a particular animal which was standing in one place
grazing in the distance, apparently peacefully. Then it gave a mighty
shake, and it looked as if the animal's outline has suddenly ballooned
outward by about a half a diameter, and then settled back onto itself.
In fact it was a mass of flies covering the animal from head to tail.
The narrator mentioned that the caribou go into deep water to
temporarily hide from the flies. But then caribou can't eat either,
and so face a Hobson's choice.
I can only imagine what that must feel like.
Don Cates
Feb 11, 2012, 11:11:16 AM2/11/12
to
There are unstriped victims around for comparison (even other Equids
(why would that be))?
> In thinking about the effect of stripes, it occurs to me that the
> flies (actually only the females bite and suck blood) might use a
> search pattern to find prey locating very large dark objects
> preferentially or alternatively large white objects. Objects that are
> variegated or striped might not be seen as "large objects". The
> pattern breaks up the animal's outline so a predator gets confused
> about what is is looking at. That is an example of disruptive
> coloration, usually the explanation for zebra stripes in confusing
> predators like the big cats or hyenas. When zebras run together as a
> herd it is very difficult to tell just where one particular animal
> begins or ends.
Perhaps it's just an accident. Why aren't there more striped animals if
it's so useful?
For insects, this effect would work equally
> effectively for intensity (black vs white) and polarization (polarized
> vs not) variation in the object viewed.
>
>
> effectively for intensity (black vs white) and polarization (polarized
> vs not) variation in the object viewed.
>
>
Kalkidas
Feb 11, 2012, 11:29:41 AM2/11/12
to
are, and have always been, dark-colored), it would seem that the
coloration is irrelevant to survival of the species.
So why attribute "anti-irritation" features to "evolution" (i.e. natural
selection), if such features do not affect the survival of the species?
This is clearly another case of "has nothing to do with evolution but we
have to say it does anyway".
Friar Broccoli
Feb 11, 2012, 11:28:10 AM2/11/12
to
explanation for zebra stripes", not even suggesting he believes it.
Do you have a problem with folks presenting hypothesis?
Do something useful. Go find a creationist to fight with.
> Perhaps it's just an accident. Why aren't there more striped animals if
> it's so useful?
>> For insects, this effect would work equally
>> effectively for intensity (black vs white) and polarization (polarized
>> vs not) variation in the object viewed.
>>
>>
>
>
--
I consider ALL arguments in support of my views
chris thompson
Feb 11, 2012, 12:24:49 PM2/11/12
to
Note that some of the illustrations are paintings, but many are
photographs.
Don't get out much, eh?
>
> So why attribute "anti-irritation" features to "evolution" (i.e. natural
> selection), if such features do not affect the survival of the species?
selection is not at all concerned with "survival of the species". It
is concerned with the reproductive success of individuals.
As for "anti-irritation features" all I can surmise is that you have
never gone camping in upstate New York or, worse, Wisconsin in Spring
or Summer. "Anti-irritation" is typical scientific understatement.
Those biting flies are a heck of a lot worse than simple irritation.
When I googled for articles (using tail swishing flies) I unexpectedly
came up with a large number of articles concerned with domestic horses
and cattle, and the effects of tail-docking on their health. With
docked tails, horses and cattle cannot swat (or at least temporarily
scare off) flies. They suffer greatly. People look at those animals in
pastures wagging their tails and think "Oh, how pretty". It predator-
avoidance, plain and simple. Herd animals even stand close to one
another so they can reciprocally swish their tails at spots they
wouldn't normally be able to reach. And alpha males are known to
suffer even more from these critters because (a) they're spending too
much time defending their harem to engage in protective behaviors and
(b) they cannot engage in that sort of reciprocal behavior- they are
just too aggressive. (Read Zimmer's _Parasite Rex_ for more
information and (somewhat old) literature citations.)
That's just some indication of how bad those flies are. Get outside
this summer, and leave the Deep Woods Off at home. You'll understand.
>
> This is clearly another case of "has nothing to do with evolution but we
> have to say it does anyway".
little if any understanding of the topic, and less real-world
experience.
Chris
Richard Norman
Feb 11, 2012, 12:33:48 PM2/11/12
to
On Sat, 11 Feb 2012 11:28:10 -0500, Friar Broccoli <eli...@gmail.com>
wrote:
Actually I don't mind at all being pressed on a point especially when
I, myself, have been highly critical of just-so explanations. (OK, I
really do squirm when challenged but I have to accept it as part of
the game.)
Since this is somewhat out of my own specialized area of interest, I
really don't know what the general sentiment is among evolutionary
biologists about why, if highly specialized animals like giraffes or
zebras or whatever have good evolutionary explanations, then why
aren't there more examples of that specialization? And, since my
retirement, I can't just walk over to the guy in the office next door
and ask him.
I don't know of any specific information dealing with horse flies and
zebras in the context of disruptive coloration -- that was proposed as
a hypothesis that needs study -- but the notion of disruptive
coloration does have a large experimental basis. For example, a
symposium on "Disruptive and cryptic coloration" was published by Proc
Roy Soc B (Proceedings of the Royal Society, a rather prestigious
British journal)
http://rspb.royalsocietypublishing.org/content/273/1600/2425.short
Of special interest to this discussion is the paper "Empirical tests
of the role of disruptive coloration in reducing detectability" which
from the title would seem to answer Don Cates' question. The abstract
says: "Collectively, our results provide independent support for the
survival value of disruptive markings "
http://rspb.royalsocietypublishing.org/content/274/1615/1325.full
Don Cates essentially said "show me the data" and my response is "here
is the data". At least here is data about disruptive coloration. That
it applies to zebras and flies is another story. As to zebras and the
big carnivorous predators, just use Google scholar to search
"disruptive coloration zebra" although you do have to be careful to
weed out those papers dealing with the zebra fish.
wrote:
I, myself, have been highly critical of just-so explanations. (OK, I
really do squirm when challenged but I have to accept it as part of
the game.)
Since this is somewhat out of my own specialized area of interest, I
really don't know what the general sentiment is among evolutionary
biologists about why, if highly specialized animals like giraffes or
zebras or whatever have good evolutionary explanations, then why
aren't there more examples of that specialization? And, since my
retirement, I can't just walk over to the guy in the office next door
and ask him.
I don't know of any specific information dealing with horse flies and
zebras in the context of disruptive coloration -- that was proposed as
a hypothesis that needs study -- but the notion of disruptive
coloration does have a large experimental basis. For example, a
symposium on "Disruptive and cryptic coloration" was published by Proc
Roy Soc B (Proceedings of the Royal Society, a rather prestigious
British journal)
http://rspb.royalsocietypublishing.org/content/273/1600/2425.short
Of special interest to this discussion is the paper "Empirical tests
of the role of disruptive coloration in reducing detectability" which
from the title would seem to answer Don Cates' question. The abstract
says: "Collectively, our results provide independent support for the
survival value of disruptive markings "
http://rspb.royalsocietypublishing.org/content/274/1615/1325.full
Don Cates essentially said "show me the data" and my response is "here
is the data". At least here is data about disruptive coloration. That
it applies to zebras and flies is another story. As to zebras and the
big carnivorous predators, just use Google scholar to search
"disruptive coloration zebra" although you do have to be careful to
weed out those papers dealing with the zebra fish.
chris thompson
Feb 11, 2012, 12:27:41 PM2/11/12
to
Horvath et al. 2010. An unexpected advantage of whiteness in horses:
the most horsefly-proof horse has a depolarizing white coat. Proc.
Royal Soc. B. 277:1643.
Abstract:
White horses frequently suffer from malign skin cancer and visual
deficiencies owing to their high sensitivity to the ultraviolet solar
radiation. Furthermore, in the wild, white horses suffer a larger
predation risk than dark individuals because they can more easily be
detected. In spite of their greater vulnerability, white horses have
been highly appreciated for centuries owing to their natural rarity.
Here, we show that blood-sucking tabanid flies, known to transmit
disease agents to mammals, are less attracted to white than dark
horses. We also demonstrate that tabanids use reflected polarized
light from the coat as a signal to find a host. The attraction of
tabanids to mainly black and brown fur coats is explained by positive
polarotaxis. As the host's colour determines its attractiveness to
tabanids, this parameter has a strong influence on the parasite load
of the host. Although we have studied only the tabanid–horse
interaction, our results can probably be extrapolated to other host
animals of polarotactic tabanids, as the reflection–polarization
characteristics of the host's body surface are physically the same,
and thus not species-dependent.
Chris
Kalkidas
Feb 11, 2012, 12:54:39 PM2/11/12
to
hand waving and personal insults.
If dark coloration in horses is a disadvantage to the survival
of individuals, why are most horses dark colored and still surviving
quite well?
Evolutionary explanations must give the details of the alleged
evolution. If they don't, then it is misleading to call them
"evolutionary" explanations, It's just a version of the "evolutiondidit"
dogma.
jillery
Feb 11, 2012, 1:01:28 PM2/11/12
to
On Sat, 11 Feb 2012 10:11:16 -0600, Don Cates <caHOR...@mts.net>
Just because one species has stumbled upon a particular beneficial
trick (the benefit being defined by the environment BTW), there is no
reason to suppose that other animals can or should implement the same
trick as well. According to evolution, each species responds to its
environment, but its future response is contingent on it current
genome. Plus there are different strategies for dealing with the same
problem. Perhaps some animals have a thicker hide, or taste bad to
the flies, or they live where the flies aren't so common.
Flying creatures have tremendous advantages over non-flying creatures.
So why don't all animals fly? Your question implies assumptions
closer to Intelligent Design than to evolution.
trick (the benefit being defined by the environment BTW), there is no
reason to suppose that other animals can or should implement the same
trick as well. According to evolution, each species responds to its
environment, but its future response is contingent on it current
genome. Plus there are different strategies for dealing with the same
problem. Perhaps some animals have a thicker hide, or taste bad to
the flies, or they live where the flies aren't so common.
Flying creatures have tremendous advantages over non-flying creatures.
So why don't all animals fly? Your question implies assumptions
closer to Intelligent Design than to evolution.
chris thompson
Feb 11, 2012, 12:58:38 PM2/11/12
to
protective coloration to large predators (apparently not insects,
though) and light-colored equines suffer more from visual problems and
skin cancer (um, same as human albinos, you know).
>
> Evolutionary explanations must give the details of the alleged
> evolution. If they don't, then it is misleading to call them
> "evolutionary" explanations, It's just a version of the "evolutiondidit"
> dogma.
Richard Norman or me.
Chris
PS: http://rspb.royalsocietypublishing.org/content/277/1688/1643.long
Kalkidas
Feb 11, 2012, 1:24:31 PM2/11/12
to
problems?
>> Evolutionary explanations must give the details of the alleged
>> evolution. If they don't, then it is misleading to call them
>> "evolutionary" explanations, It's just a version of the "evolutiondidit"
>> dogma.
>
> And I bet you haven't tracked down a single reference provided by
> Richard Norman or me.
make sense either.
Walter Bushell
Feb 11, 2012, 1:34:48 PM2/11/12
to
In article <l2adj7t91igcik7lb...@4ax.com>,
that all animals would get it either. Most primates specialized in other
attributes and our line went just about extinct fairly recently.
--
It is the nature of the human species to reject what is true but unpleasant
and to embrace what is obviously false but comforting. -- H. L. Mencken
jillery <69jp...@gmail.com> wrote:
>
> Just because one species has stumbled upon a particular beneficial
> trick (the benefit being defined by the environment BTW), there is no
> reason to suppose that other animals can or should implement the same
> trick as well. According to evolution, each species responds to its
> environment, but its future response is contingent on it current
> genome. Plus there are different strategies for dealing with the same
> problem. Perhaps some animals have a thicker hide, or taste bad to
> the flies, or they live where the flies aren't so common.
>
>
> Flying creatures have tremendous advantages over non-flying creatures.
> So why don't all animals fly? Your question implies assumptions
> closer to Intelligent Design than to evolution.
Just because being tool using sophants is a great advantage doesn't mean
>
> Just because one species has stumbled upon a particular beneficial
> trick (the benefit being defined by the environment BTW), there is no
> reason to suppose that other animals can or should implement the same
> trick as well. According to evolution, each species responds to its
> environment, but its future response is contingent on it current
> genome. Plus there are different strategies for dealing with the same
> problem. Perhaps some animals have a thicker hide, or taste bad to
> the flies, or they live where the flies aren't so common.
>
>
> Flying creatures have tremendous advantages over non-flying creatures.
> So why don't all animals fly? Your question implies assumptions
> closer to Intelligent Design than to evolution.
that all animals would get it either. Most primates specialized in other
attributes and our line went just about extinct fairly recently.
--
It is the nature of the human species to reject what is true but unpleasant
and to embrace what is obviously false but comforting. -- H. L. Mencken
Friar Broccoli
Feb 11, 2012, 1:43:51 PM2/11/12
to
> Since this is somewhat out of my own specialized area of interest, I
> really don't know what the general sentiment is among evolutionary
> biologists about why, if highly specialized animals like giraffes or
> zebras or whatever have good evolutionary explanations, then why
> aren't there more examples of that specialization?
(1) If most or all animals did it, the flies would adapt by changing
their detection strategy removing the utility of the adaptation.
(2) Trade-off between not being seen by big predators (cats and canines)
and small ones (flies).
Also, not a lot of horses left in africa, three species of zebra and
numerous subspecies suggesting the striped formula is working best right
now.
Do you have any other hypothesis?
On the other hand, I just checked and zebras are slower than horses and
wildebeests which is the opposite of what I would have expected if my
hypothesis (2) were correct.
> And, since my
> retirement, I can't just walk over to the guy in the office next door
> and ask him.
>
> I don't know of any specific information dealing with horse flies and
> zebras in the context of disruptive coloration -- that was proposed as
> a hypothesis that needs study -- but the notion of disruptive
> coloration does have a large experimental basis. For example, a
> symposium on "Disruptive and cryptic coloration" was published by Proc
> Roy Soc B (Proceedings of the Royal Society, a rather prestigious
> British journal)
> http://rspb.royalsocietypublishing.org/content/273/1600/2425.short
>
> Of special interest to this discussion is the paper "Empirical tests
> of the role of disruptive coloration in reducing detectability" which
> from the title would seem to answer Don Cates' question. The abstract
> says: "Collectively, our results provide independent support for the
> survival value of disruptive markings "
> http://rspb.royalsocietypublishing.org/content/274/1615/1325.full
>
> Don Cates essentially said "show me the data" and my response is "here
> is the data". At least here is data about disruptive coloration. That
> it applies to zebras and flies is another story. As to zebras and the
> big carnivorous predators, just use Google scholar to search
> "disruptive coloration zebra" although you do have to be careful to
> weed out those papers dealing with the zebra fish.
>
Don Cates
Feb 11, 2012, 1:58:47 PM2/11/12
to
(morphological, genetic, biogeographical, etc). What is not so clear,
although there is *some* evidence, is how much of it is adaptive. You
seem to think that adaptation=evolution and Chris seems to want to
explain most (all?) evolution as adaptive, but it is probable that most
evolutionary change is neutral and adaptive explanations should be well
evidenced, not assumed.
>>>> No, it's clearly another case of someone sitting at a computer who has
>>>> little if any understanding of the topic, and less real-world
>>>> experience.
>>>
>>> It is as I said. You have given no evolutionary explanation. Just vague
>>> hand waving and personal insults.
>>>
>>> If dark coloration in horses is a disadvantage to the survival
>>> of individuals, why are most horses dark colored and still surviving
>>> quite well?
>>
>> Because there are competing pressures. Dark equines have better
>> protective coloration to large predators (apparently not insects,
>> though) and light-colored equines suffer more from visual problems and
>> skin cancer (um, same as human albinos, you know).
>
> Then why are light colored horses still around, if they have so many
> problems?
>
advantage that overcomes all the negatives; a significant number of
people like them that way.
>>> Evolutionary explanations must give the details of the alleged
>>> evolution. If they don't, then it is misleading to call them
>>> "evolutionary" explanations, It's just a version of the "evolutiondidit"
>>> dogma.
>>
>> And I bet you haven't tracked down a single reference provided by
>> Richard Norman or me.
>
> Do those "references" say the same things you're saying? Then they don't
> make sense either.
>
chris thompson
Feb 11, 2012, 2:02:08 PM2/11/12
to
allele for sickle cell disease still around? It's a horrible disease,
but in the heterozygote it confers an advantage against malaria! Until
about 2001, when HIV took over the slot, malaria was the number one
cause of death worldwide! ANYTHING that gave a survival/reproductive
advantage in the face of malaria (and it's a LOT worse in infants than
adults) would be selected for.
>
> >> Evolutionary explanations must give the details of the alleged
> >> evolution. If they don't, then it is misleading to call them
> >> "evolutionary" explanations, It's just a version of the "evolutiondidit"
> >> dogma.
>
> > And I bet you haven't tracked down a single reference provided by
> > Richard Norman or me.
>
> Do those "references" say the same things you're saying? Then they don't
> make sense either.
world-view.
Go to the references. When something is too hard to understand, post a
question and many people here will explain the answer.
Chris
jillery
Feb 11, 2012, 2:51:49 PM2/11/12
to
On Sat, 11 Feb 2012 13:34:48 -0500, Walter Bushell <pr...@panix.com>
wrote:
>In article <l2adj7t91igcik7lb...@4ax.com>,
> jillery <69jp...@gmail.com> wrote:
>
>>
>> Just because one species has stumbled upon a particular beneficial
>> trick (the benefit being defined by the environment BTW), there is no
>> reason to suppose that other animals can or should implement the same
>> trick as well. According to evolution, each species responds to its
>> environment, but its future response is contingent on it current
>> genome. Plus there are different strategies for dealing with the same
>> problem. Perhaps some animals have a thicker hide, or taste bad to
>> the flies, or they live where the flies aren't so common.
>>
>>
>> Flying creatures have tremendous advantages over non-flying creatures.
>> So why don't all animals fly? Your question implies assumptions
>> closer to Intelligent Design than to evolution.
>
>Just because being tool using sophants is a great advantage doesn't mean
>that all animals would get it either. Most primates specialized in other
>attributes and our line went just about extinct fairly recently.
True dat. That species don't have the best mix of features for a
given environment is the best single argument I can think of against
Intelligent Design and for natural evolution.
wrote:
>In article <l2adj7t91igcik7lb...@4ax.com>,
> jillery <69jp...@gmail.com> wrote:
>
>>
>> Just because one species has stumbled upon a particular beneficial
>> trick (the benefit being defined by the environment BTW), there is no
>> reason to suppose that other animals can or should implement the same
>> trick as well. According to evolution, each species responds to its
>> environment, but its future response is contingent on it current
>> genome. Plus there are different strategies for dealing with the same
>> problem. Perhaps some animals have a thicker hide, or taste bad to
>> the flies, or they live where the flies aren't so common.
>>
>>
>> Flying creatures have tremendous advantages over non-flying creatures.
>> So why don't all animals fly? Your question implies assumptions
>> closer to Intelligent Design than to evolution.
>
>Just because being tool using sophants is a great advantage doesn't mean
>that all animals would get it either. Most primates specialized in other
>attributes and our line went just about extinct fairly recently.
given environment is the best single argument I can think of against
Intelligent Design and for natural evolution.
Don Cates
Feb 11, 2012, 3:16:25 PM2/11/12
to
both parties) that a selectable adaptation is required for evolution to
be invoked. Perhaps I've been reading too much Sandwalk.
> Do you have a problem with folks presenting hypothesis?
>
> Do something useful. Go find a creationist to fight with.
>
assumption is worthwhile.
>
>
>
>> Perhaps it's just an accident. Why aren't there more striped animals if
>> it's so useful?
>>> For insects, this effect would work equally
>>> effectively for intensity (black vs white) and polarization (polarized
>>> vs not) variation in the object viewed.
>>>
>>>
>>
>>
>
>
--
>
>
>> Perhaps it's just an accident. Why aren't there more striped animals if
>> it's so useful?
>>> For insects, this effect would work equally
>>> effectively for intensity (black vs white) and polarization (polarized
>>> vs not) variation in the object viewed.
>>>
>>>
>>
>>
>
>
--
Don Cates
Feb 11, 2012, 3:53:55 PM2/11/12
to
>
> Since this is somewhat out of my own specialized area of interest, I
> really don't know what the general sentiment is among evolutionary
> biologists about why, if highly specialized animals like giraffes or
> zebras or whatever have good evolutionary explanations, then why
> aren't there more examples of that specialization? And, since my
> retirement, I can't just walk over to the guy in the office next door
> and ask him.
>
> I don't know of any specific information dealing with horse flies and
> zebras in the context of disruptive coloration -- that was proposed as
> a hypothesis that needs study -- but the notion of disruptive
> coloration does have a large experimental basis. For example, a
> symposium on "Disruptive and cryptic coloration" was published by Proc
> Roy Soc B (Proceedings of the Royal Society, a rather prestigious
> British journal)
> http://rspb.royalsocietypublishing.org/content/273/1600/2425.short
Hmmm, moths and birds, but with some relevance.
> Since this is somewhat out of my own specialized area of interest, I
> really don't know what the general sentiment is among evolutionary
> biologists about why, if highly specialized animals like giraffes or
> zebras or whatever have good evolutionary explanations, then why
> aren't there more examples of that specialization? And, since my
> retirement, I can't just walk over to the guy in the office next door
> and ask him.
>
> I don't know of any specific information dealing with horse flies and
> zebras in the context of disruptive coloration -- that was proposed as
> a hypothesis that needs study -- but the notion of disruptive
> coloration does have a large experimental basis. For example, a
> symposium on "Disruptive and cryptic coloration" was published by Proc
> Roy Soc B (Proceedings of the Royal Society, a rather prestigious
> British journal)
> http://rspb.royalsocietypublishing.org/content/273/1600/2425.short
>
> Of special interest to this discussion is the paper "Empirical tests
> of the role of disruptive coloration in reducing detectability" which
> from the title would seem to answer Don Cates' question. The abstract
> says: "Collectively, our results provide independent support for the
> survival value of disruptive markings "
> http://rspb.royalsocietypublishing.org/content/274/1615/1325.full
This comclusion was somewhat troubling.
> Of special interest to this discussion is the paper "Empirical tests
> of the role of disruptive coloration in reducing detectability" which
> from the title would seem to answer Don Cates' question. The abstract
> says: "Collectively, our results provide independent support for the
> survival value of disruptive markings "
> http://rspb.royalsocietypublishing.org/content/274/1615/1325.full
"Our disruptively patterned non-background-matching moths also had the
lowest overall survivorship, indicating that disruptive coloration alone
may not provide significant protection from predators."
This is more promising.
"More recent analyses have confirmed that disruptive markings can indeed
make inferences related to prey shape more challenging to observers
(Osorio & Srinivasan 1991; Stevens & Cuthill 2006). "
The study is considering being detected by predators at all rather than
being hard to pick out individuals from a crowd. So it has, perhaps,
more relevance to the zebra/fly scenario than the zebra/lion one.
>
> Don Cates essentially said "show me the data" and my response is "here
> is the data". At least here is data about disruptive coloration. That
> it applies to zebras and flies is another story. As to zebras and the
> big carnivorous predators, just use Google scholar to search
> "disruptive coloration zebra" although you do have to be careful to
> weed out those papers dealing with the zebra fish.
>
Well, I did just that and I couldn't find much in the way of data (lots
> Don Cates essentially said "show me the data" and my response is "here
> is the data". At least here is data about disruptive coloration. That
> it applies to zebras and flies is another story. As to zebras and the
> big carnivorous predators, just use Google scholar to search
> "disruptive coloration zebra" although you do have to be careful to
> weed out those papers dealing with the zebra fish.
>
of speculation). Did you have any particular study in mind?
Kalkidas
Feb 11, 2012, 4:07:12 PM2/11/12
to
chris thompson <chris.li...@gmail.com> wrote in
news:0f79c92a-6443-4aff...@o13g2000vbf.googlegroups.com:
I don't think you've gone to the references yourself. Otherwise, you
could explain why "evolution" needs to be invoked to explain why horses
are of different colors.
news:0f79c92a-6443-4aff...@o13g2000vbf.googlegroups.com:
could explain why "evolution" needs to be invoked to explain why horses
are of different colors.
Burkhard
Feb 11, 2012, 4:08:59 PM2/11/12
to
would seem that having guns and cannon was irrelevant for the creation
of a Spanish empire in Latin America
Richard Norman
Feb 11, 2012, 4:31:02 PM2/11/12
to
On Sat, 11 Feb 2012 13:43:51 -0500, Friar Broccoli <eli...@gmail.com>
wrote:
>On 2012-02-11 12:33, Richard Norman wrote:
<major snippage>
>> Since this is somewhat out of my own specialized area of interest, I
>> really don't know what the general sentiment is among evolutionary
>> biologists about why, if highly specialized animals like giraffes or
>> zebras or whatever have good evolutionary explanations, then why
>> aren't there more examples of that specialization?
>
>I can suggest the two all too obvious hypothesis:
>(1) If most or all animals did it, the flies would adapt by changing
>their detection strategy removing the utility of the adaptation.
>(2) Trade-off between not being seen by big predators (cats and canines)
>and small ones (flies).
>
>Also, not a lot of horses left in africa, three species of zebra and
>numerous subspecies suggesting the striped formula is working best right
>now.
>
>Do you have any other hypothesis?
>
>On the other hand, I just checked and zebras are slower than horses and
>wildebeests which is the opposite of what I would have expected if my
>hypothesis (2) were correct.
>
First, it is not at all clear that fly business is really the major
evolutionary factor controlling coat color in zebras. That stripes
offer some protection against flies may or may not offset any effect
on predation by hyenas and the big cats, the major predators on
zebras.
Second, my iimpression is that the flies also feed on pretty much any
large mammals they can find. Prime examples would be the bovines,
mainly antelope but also Cape Buffalo and others. There do exist
striped antelope -- the Zebra Duiker, for example -- so why not more
of these?
There are a wide variety of biting flies in Africa besides the
Tabanids but probably all have similar vision. Some flies can pierce
Hippotamus hide. Many of these breed in water and attraction to
horizontally polarized light is a particular feature of aquatic
insects since light reflected from the surface of water tends to be
horizontally polarized.
Contrary to your hypothesis (2): stripes are argued to be protective
against both predatory carnivores and biting flies. At least stripes
in the way that zebras behave in a herd. Solitary zebras might face
different selection pressures.
The real issue is finding evidence to support any definitive
conclusion. It is not difficult to test how well flies are attracted
to different visual patterns including color, intensity, and
polarization. It is difficult to test how well a lion can take down
prey of different visual patterns. It is probably virtually
impossible to test the relative significance of protection against
biting flies vs. protection against carnivorous predators.
As to hypothesis (1): there are known examples of frequency dependent
selection where being in a minority can be advantageous. It is
difficult to see what advantage there is, though, in preventing
members of different species adapting the same strategy. You are
arguing "if I do it, then I may survive but in the long run things may
turn out badly". Evolution doesn't seem to take the long view in that
way.
wrote:
>On 2012-02-11 12:33, Richard Norman wrote:
>> Since this is somewhat out of my own specialized area of interest, I
>> really don't know what the general sentiment is among evolutionary
>> biologists about why, if highly specialized animals like giraffes or
>> zebras or whatever have good evolutionary explanations, then why
>> aren't there more examples of that specialization?
>
>I can suggest the two all too obvious hypothesis:
>(1) If most or all animals did it, the flies would adapt by changing
>their detection strategy removing the utility of the adaptation.
>(2) Trade-off between not being seen by big predators (cats and canines)
>and small ones (flies).
>
>Also, not a lot of horses left in africa, three species of zebra and
>numerous subspecies suggesting the striped formula is working best right
>now.
>
>Do you have any other hypothesis?
>
>On the other hand, I just checked and zebras are slower than horses and
>wildebeests which is the opposite of what I would have expected if my
>hypothesis (2) were correct.
>
evolutionary factor controlling coat color in zebras. That stripes
offer some protection against flies may or may not offset any effect
on predation by hyenas and the big cats, the major predators on
zebras.
Second, my iimpression is that the flies also feed on pretty much any
large mammals they can find. Prime examples would be the bovines,
mainly antelope but also Cape Buffalo and others. There do exist
striped antelope -- the Zebra Duiker, for example -- so why not more
of these?
There are a wide variety of biting flies in Africa besides the
Tabanids but probably all have similar vision. Some flies can pierce
Hippotamus hide. Many of these breed in water and attraction to
horizontally polarized light is a particular feature of aquatic
insects since light reflected from the surface of water tends to be
horizontally polarized.
Contrary to your hypothesis (2): stripes are argued to be protective
against both predatory carnivores and biting flies. At least stripes
in the way that zebras behave in a herd. Solitary zebras might face
different selection pressures.
The real issue is finding evidence to support any definitive
conclusion. It is not difficult to test how well flies are attracted
to different visual patterns including color, intensity, and
polarization. It is difficult to test how well a lion can take down
prey of different visual patterns. It is probably virtually
impossible to test the relative significance of protection against
biting flies vs. protection against carnivorous predators.
As to hypothesis (1): there are known examples of frequency dependent
selection where being in a minority can be advantageous. It is
difficult to see what advantage there is, though, in preventing
members of different species adapting the same strategy. You are
arguing "if I do it, then I may survive but in the long run things may
turn out badly". Evolution doesn't seem to take the long view in that
way.
chris thompson
Feb 11, 2012, 3:46:59 PM2/11/12
to
ruminants seem to have a selective advantage- in one sense (i.e.,
biting flies don't target them). But overall, drift is probably a
stronger force than selection.
Chris
Richard Norman
Feb 11, 2012, 4:57:30 PM2/11/12
to
On Sat, 11 Feb 2012 14:53:55 -0600, Don Cates <caHOR...@mts.net>
As I indicated in a different branch of this thread, it is rather
difficult to test how well lions take down zebras of different stripe
patterns. It is rather easier to study fish or moths or birds. So
you do the best you can and speculate on the basis of the evidence you
can garner so that your speculation is persuasive and convincing to
people who also have experience in ecology and evolution and animal
behavior. So credible speculation forms the basis of many stories
that would otherwise be dismissed simply as just-so. How much money
and time and career do you want to spend on each little aspect of
evolutionary speculation and are there deeper and more significant
questions that better deserve your time and effort? That is the real
issue.
difficult to test how well lions take down zebras of different stripe
patterns. It is rather easier to study fish or moths or birds. So
you do the best you can and speculate on the basis of the evidence you
can garner so that your speculation is persuasive and convincing to
people who also have experience in ecology and evolution and animal
behavior. So credible speculation forms the basis of many stories
that would otherwise be dismissed simply as just-so. How much money
and time and career do you want to spend on each little aspect of
evolutionary speculation and are there deeper and more significant
questions that better deserve your time and effort? That is the real
issue.
chris thompson
Feb 11, 2012, 5:38:57 PM2/11/12
to
On Feb 11, 4:07 pm, Kalkidas <e...@joes.pub> wrote:
Already did that- but you didn't read the references. Keep on with
your willful ignorance.
Chris
your willful ignorance.
Chris
chris thompson
Feb 11, 2012, 5:44:34 PM2/11/12
to
On Feb 11, 4:31 pm, Richard Norman <r_s_nor...@comcast.net> wrote:
> On Sat, 11 Feb 2012 13:43:51 -0500, Friar Broccoli <elia...@gmail.com>
Big predators kill an individual all at once. Flies kill individuals
over a relatively long period of time. This supports your idea.
>
> Second, my iimpression is that the flies also feed on pretty much any
> large mammals they can find. Prime examples would be the bovines,
> mainly antelope but also Cape Buffalo and others. There do exist
> striped antelope -- the Zebra Duiker, for example -- so why not more
> of these?
>
> There are a wide variety of biting flies in Africa besides the
> Tabanids but probably all have similar vision. Some flies can pierce
Assumption is reasonable, but no evidence (at least, none presented).
Perhaps some flies are specialized to see certain kinds of fur?
Chris
> On Sat, 11 Feb 2012 13:43:51 -0500, Friar Broccoli <elia...@gmail.com>
over a relatively long period of time. This supports your idea.
>
> Second, my iimpression is that the flies also feed on pretty much any
> large mammals they can find. Prime examples would be the bovines,
> mainly antelope but also Cape Buffalo and others. There do exist
> striped antelope -- the Zebra Duiker, for example -- so why not more
> of these?
>
> There are a wide variety of biting flies in Africa besides the
> Tabanids but probably all have similar vision. Some flies can pierce
Perhaps some flies are specialized to see certain kinds of fur?
Chris
Steven L.
Feb 11, 2012, 5:48:17 PM2/11/12
to
"Richard Norman" <r_s_n...@comcast.net> wrote in message
news:u80cj79idlcqof7et...@4ax.com:
> In thinking about the effect of stripes, it occurs to me that the
> flies (actually only the females bite and suck blood) might use a
> search pattern to find prey locating very large dark objects
> preferentially or alternatively large white objects. Objects that are
> variegated or striped might not be seen as "large objects". The
> pattern breaks up the animal's outline so a predator gets confused
> about what is is looking at. That is an example of disruptive
> coloration, usually the explanation for zebra stripes in confusing
> predators like the big cats or hyenas.
World War I, when it was called "dazzle camouflage." It broke up the
outline of the ship to confuse German U-boat crews looking at the ships
through their periscopes.
http://www.woostercollective.com/zebra-striped-camouflage.jpg
http://visboo.com/img/photos/world-war-1-dazzle-camouflage.jpg
Later on, along came radar which negated effectiveness of visual
camouflage, which is why dazzle was eventually dropped in World War II.
-- Steven L.
Steven L.
Feb 11, 2012, 5:52:30 PM2/11/12
to
"Walter Bushell" <pr...@panix.com> wrote in message
news:proto-10153B....@news.panix.com:
> In article <l2adj7t91igcik7lb...@4ax.com>,
> jillery <69jp...@gmail.com> wrote:
>
> >
> > Just because one species has stumbled upon a particular beneficial
> > trick (the benefit being defined by the environment BTW), there is no
> > reason to suppose that other animals can or should implement the same
> > trick as well. According to evolution, each species responds to its
> > environment, but its future response is contingent on it current
> > genome. Plus there are different strategies for dealing with the same
> > problem. Perhaps some animals have a thicker hide, or taste bad to
> > the flies, or they live where the flies aren't so common.
> >
> >
> > Flying creatures have tremendous advantages over non-flying creatures.
> > So why don't all animals fly? Your question implies assumptions
> > closer to Intelligent Design than to evolution.
>
> Just because being tool using sophants is a great advantage doesn't mean
> that all animals would get it either. Most primates specialized in other
> attributes and our line went just about extinct fairly recently.
having that problem.
While Homo Sapiens was an endangered species, down to just a few
thousand individuals, Neanderthals weren't suffering that same
tribulation. Perhaps their descendants would have created a
civilization eventually, if they hadn't been displaced by the newly
arriving Homo Sapiens.
But I do notice something about you: Where Man is concerned, you are
quite the cynic.
-- Steven L.
Richard Norman
Feb 11, 2012, 7:09:00 PM2/11/12
to
separate species. What is found is that the eyes, especially Dipteran
eyes, tend to be rather similar. There is absolutely no reason to
suspect that different species in one genus or different genera in one
family or different families in one suborder are so different in
vision that they can only see some kinds of fur but not others. Now
if you ask about search patterns for predation or parasitism or
foraging or mating, that is a very different thing.
Read my other post about credible speculation and why we accept it in
place of absolute certainty about every tiniest little detail of every
species in the world.
Glenn
Feb 11, 2012, 7:21:29 PM2/11/12
to
On Feb 10, 4:33 pm, Metspitzer <kilow...@charter.net> wrote:
> Why zebras evolved their characteristic black-and-white stripes has
> been the subject of decades of debate among scientists.
snip
> Why zebras evolved their characteristic black-and-white stripes has
> been the subject of decades of debate among scientists.
>
> "We created an experimental set-up where we painted the different
> patterns onto boards," Dr Akesson told BBC Nature.
>
> http://www.bbc.co.uk/nature/16944753
Apparently some zebras have a smell that tsetse flies avoid.
> "We created an experimental set-up where we painted the different
> patterns onto boards," Dr Akesson told BBC Nature.
>
> http://www.bbc.co.uk/nature/16944753
http://www.healthcare-today.co.uk/news/tsetse-flies-repelled-by-zebra-smell/15324/
Of course, tsetse are not the only blood suckers that can transmit
diseases; an alternative to this paper machete science study that
currently contaminates the minds of many is that during the course of
evolution of the Madagascar zebra, a now extinct sucker carried a
virus which produced the first stripes. When the now extinct
Madagascar zebra rafted to Africa some 4.3 to 6.2 million years ago,
the stripes became fixed in the small population due to bottleneck.
Kalkidas
Feb 11, 2012, 9:03:06 PM2/11/12
to
On 2/11/2012 2:08 PM, Burkhard wrote:
> On Feb 11, 4:29 pm, Kalkidas<e...@joes.pub> wrote:
[snip]
> On Feb 11, 4:29 pm, Kalkidas<e...@joes.pub> wrote:
>> Since horses of all colors are still around (and I believe most of them
>> are, and have always been, dark-colored), it would seem that the
>> coloration is irrelevant to survival of the species.
>
> Quite. And since there are still indigenous tribes in the amazon, it
> would seem that having guns and cannon was irrelevant for the creation
> of a Spanish empire in Latin America
natural selection lost that battle.
jillery
Feb 11, 2012, 10:00:39 PM2/11/12
to
saying, that reasonable speculation, particularly that which claims
related evidence, is not the same thing as a just-so story, where the
evidence is either unrelated or assumed. Is that correct?
William Morse
Feb 11, 2012, 10:03:19 PM2/11/12
to
On 02/11/2012 01:06 AM, Richard Norman wrote:
> On Fri, 10 Feb 2012 23:31:15 -0600, Don Cates<caHOR...@mts.net>
> wrote:
>
>> On 10/02/2012 7:46 PM, Richard Norman wrote:
>>> On Fri, 10 Feb 2012 15:48:01 -0800 (PST), chris thompson
> On Fri, 10 Feb 2012 23:31:15 -0600, Don Cates<caHOR...@mts.net>
> wrote:
>
>> On 10/02/2012 7:46 PM, Richard Norman wrote:
>>> <chris.li...@gmail.com> wrote:
>>>
>>>> On Feb 10, 6:33 pm, Metspitzer<kilow...@charter.net> wrote:
>>>>> Why zebras evolved their characteristic black-and-white stripes has
>>>>> been the subject of decades of debate among scientists.
>>>>>
>>>> On Feb 10, 6:33 pm, Metspitzer<kilow...@charter.net> wrote:
>>>>> Why zebras evolved their characteristic black-and-white stripes has
>>>>> been the subject of decades of debate among scientists.
>>>>>
>>>>> "We created an experimental set-up where we painted the different
>>>>> patterns onto boards," Dr Akesson told BBC Nature.
>>>>>
>>>>> http://www.bbc.co.uk/nature/16944753
>>>>
>>>>> patterns onto boards," Dr Akesson told BBC Nature.
>>>>>
>>>>> http://www.bbc.co.uk/nature/16944753
>>>>
> In thinking about the effect of stripes, it occurs to me that the
> flies (actually only the females bite and suck blood) might use a
> search pattern to find prey locating very large dark objects
> preferentially or alternatively large white objects. Objects that are
> variegated or striped might not be seen as "large objects". The
> pattern breaks up the animal's outline so a predator gets confused
> about what is is looking at. That is an example of disruptive
> coloration, usually the explanation for zebra stripes in confusing
> flies (actually only the females bite and suck blood) might use a
> search pattern to find prey locating very large dark objects
> preferentially or alternatively large white objects. Objects that are
> variegated or striped might not be seen as "large objects". The
> pattern breaks up the animal's outline so a predator gets confused
> about what is is looking at. That is an example of disruptive
> coloration, usually the explanation for zebra stripes in confusing
> predators like the big cats or hyenas. When zebras run together as a
> herd it is very difficult to tell just where one particular animal
> begins or ends. For insects, this effect would work equally
> herd it is very difficult to tell just where one particular animal
> effectively for intensity (black vs white) and polarization (polarized
> vs not) variation in the object viewed.
>
>
The other question that occurs to me is why other mammals haven't also
> vs not) variation in the object viewed.
>
>
adopted this coloration pattern if it is so effective. Perhaps it is not
that easy to evolve, but I find that hard to believe given the relative
ubiquity of banding among mammals. So why isn't striping seen in African
antelopes, that would seem to occupy a similar niche to zebras?
Bill
Burkhard
Feb 11, 2012, 10:25:30 PM2/11/12
to
Richard Norman
Feb 11, 2012, 11:07:36 PM2/11/12
to
On Sat, 11 Feb 2012 22:00:39 -0500, jillery <69jp...@gmail.com>
Reasonable speculation, based on related evidence, that uses credible
mechanisms which are credibly expected to produce the desired result
when clearly labelled as speculation or hypothesis or possibility is
preferable to just wildly bullshitting off the top of ones head. Not
every tiny detail is worth following up with absolutely convincing
evidence when there is good indirect reason to believe the details are
correct. Sometimes doing so causes you to go wrong.
Generally, a real just-so story "consistently lacks any sort of
physical evidence or ability to be verified by current or future data"
or is "applied to a postulated evolutionary mechanism for a human or
animal trait or behavior which cannot be falsified by scientific
evidence" or else "more broadly for any fantastic or improbable
explanation of a phenomenon". See EvoWiki
http://evolutionwiki.org/wiki/Just_So_Story
Explanations with at least some credible indirect evidence or
plausible mechanisms do not fit that bill.
Live with it.
In the current context, there is good actual evidence that striped
patterns similar to those of zebras attract fewer Tabanid flies than
do homogenous colors. There is also good actual evidence that in some
cases what is called disruptive coloration makes predation more
difficult. Building on these ideas means the result has some
plausibility and therefore is not really a "just-so" story.
mechanisms which are credibly expected to produce the desired result
when clearly labelled as speculation or hypothesis or possibility is
preferable to just wildly bullshitting off the top of ones head. Not
every tiny detail is worth following up with absolutely convincing
evidence when there is good indirect reason to believe the details are
correct. Sometimes doing so causes you to go wrong.
Generally, a real just-so story "consistently lacks any sort of
physical evidence or ability to be verified by current or future data"
or is "applied to a postulated evolutionary mechanism for a human or
animal trait or behavior which cannot be falsified by scientific
evidence" or else "more broadly for any fantastic or improbable
explanation of a phenomenon". See EvoWiki
http://evolutionwiki.org/wiki/Just_So_Story
Explanations with at least some credible indirect evidence or
plausible mechanisms do not fit that bill.
Live with it.
In the current context, there is good actual evidence that striped
patterns similar to those of zebras attract fewer Tabanid flies than
do homogenous colors. There is also good actual evidence that in some
cases what is called disruptive coloration makes predation more
difficult. Building on these ideas means the result has some
plausibility and therefore is not really a "just-so" story.
jillery
Feb 11, 2012, 11:59:51 PM2/11/12
to
On Sat, 11 Feb 2012 21:07:36 -0700, Richard Norman
???
>In the current context, there is good actual evidence that striped
>patterns similar to those of zebras attract fewer Tabanid flies than
>do homogenous colors. There is also good actual evidence that in some
>cases what is called disruptive coloration makes predation more
>difficult. Building on these ideas means the result has some
>plausibility and therefore is not really a "just-so" story.
That's what I thought. IIUC you recognize a fundamental difference
between reasonable speculation and just-so stories as specified above.
So arguments which conflate the two are suspect. Is that correct?
>In the current context, there is good actual evidence that striped
>patterns similar to those of zebras attract fewer Tabanid flies than
>do homogenous colors. There is also good actual evidence that in some
>cases what is called disruptive coloration makes predation more
>difficult. Building on these ideas means the result has some
>plausibility and therefore is not really a "just-so" story.
between reasonable speculation and just-so stories as specified above.
So arguments which conflate the two are suspect. Is that correct?
jillery
Feb 12, 2012, 12:03:46 AM2/12/12
to
actual point of the question?
Richard Norman
Feb 12, 2012, 1:13:31 AM2/12/12
to
On Sat, 11 Feb 2012 23:59:51 -0500, jillery <69jp...@gmail.com>
I don't want to get into a silly fight over exactly what is a just-so
story and what is not. I do not understand what you mean by arguments
which conflate the two. How do you conflate reasonable speculation
based on good actual evidence that is testable and unreasonable
speculation in the absence of any evidence or testability? These seem
opposites to me.
story and what is not. I do not understand what you mean by arguments
which conflate the two. How do you conflate reasonable speculation
based on good actual evidence that is testable and unreasonable
speculation in the absence of any evidence or testability? These seem
opposites to me.
jillery
Feb 12, 2012, 2:35:23 AM2/12/12
to
On Sat, 11 Feb 2012 23:13:31 -0700, Richard Norman
Do you not care to explain the spirit or your intent to your statement
"live with it"?
>>>In the current context, there is good actual evidence that striped
>>>patterns similar to those of zebras attract fewer Tabanid flies than
>>>do homogenous colors. There is also good actual evidence that in some
>>>cases what is called disruptive coloration makes predation more
>>>difficult. Building on these ideas means the result has some
>>>plausibility and therefore is not really a "just-so" story.
>>
>>
>>That's what I thought. IIUC you recognize a fundamental difference
>>between reasonable speculation and just-so stories as specified above.
>>So arguments which conflate the two are suspect. Is that correct?
>
>I don't want to get into a silly fight over exactly what is a just-so
>story and what is not.
Neither do I. Why are you being so defensive?
>I do not understand what you mean by arguments
>which conflate the two. How do you conflate reasonable speculation
>based on good actual evidence that is testable and unreasonable
>speculation in the absence of any evidence or testability? These seem
>opposites to me.
As they do to me. I recall several topics where anti-science
creationists have asserted, paraphrasing, that their just-so
explanations and the just-so explanations of science are functionally
and philosophically equivalent. ISTM this point comes up fairly
regularly in T.O.
"live with it"?
>>>In the current context, there is good actual evidence that striped
>>>patterns similar to those of zebras attract fewer Tabanid flies than
>>>do homogenous colors. There is also good actual evidence that in some
>>>cases what is called disruptive coloration makes predation more
>>>difficult. Building on these ideas means the result has some
>>>plausibility and therefore is not really a "just-so" story.
>>
>>
>>That's what I thought. IIUC you recognize a fundamental difference
>>between reasonable speculation and just-so stories as specified above.
>>So arguments which conflate the two are suspect. Is that correct?
>
>I don't want to get into a silly fight over exactly what is a just-so
>story and what is not.
>I do not understand what you mean by arguments
>which conflate the two. How do you conflate reasonable speculation
>based on good actual evidence that is testable and unreasonable
>speculation in the absence of any evidence or testability? These seem
>opposites to me.
creationists have asserted, paraphrasing, that their just-so
explanations and the just-so explanations of science are functionally
and philosophically equivalent. ISTM this point comes up fairly
regularly in T.O.
Friar Broccoli
Feb 12, 2012, 9:23:12 AM2/12/12
to
the suggestion that (significantly) reducing the impact of a parasite
might not have a selective advantage. A suggestion I find bizarre.
>
>> Do you have a problem with folks presenting hypothesis?
>>
> Not at all, it's the above assumption I'm complaining about.
I certainly don't know, but think the opposite question at least as
relevant: Why is it unreasonable to assume that a characteristic that
has been retained with little modification across 3 species (embracing
seven sub-species) is not under positive selective pressure?
True the exact genetic mechanism by which zebra striping is initiated
has not yet been identified, however positive characteristics are
usually easily dropped unless actively retained by selection, although
admittedly that selection could be sexual.
>
>> Do something useful. Go find a creationist to fight with.
>>
> I'm sorry you don't think pointing out the problem with making that
> assumption is worthwhile.
>>
>>
>>
>>> Perhaps it's just an accident. Why aren't there more striped animals if
>>> it's so useful?
>>>> For insects, this effect would work equally
>>>> effectively for intensity (black vs white) and polarization (polarized
>>>> vs not) variation in the object viewed.
--
I consider ALL arguments in support of my views
Richard Norman
Feb 12, 2012, 10:28:30 PM2/12/12
to
On Sun, 12 Feb 2012 02:35:23 -0500, jillery <69jp...@gmail.com>
If people declare that evidence generally accepted by the scientific
community is not really evidence then there is no point arguing with
them on the basis of evidence.
community is not really evidence then there is no point arguing with
them on the basis of evidence.
Richard Norman
Feb 12, 2012, 10:45:43 PM2/12/12
to
On Sun, 12 Feb 2012 02:35:23 -0500, jillery <69jp...@gmail.com>
My comment alluded to the fact that different people use the term
"just-so story" in different ways for different purposes. That is
something we all have to simply accept. In that sense, there is no
point in writing down a hard and fast universally accepted definition.
Why do you wonder about whether or not I am defensive? Are you being
offensive? (just to be defensive, that latter is merely a supposedly
clever word inversion)
"just-so story" in different ways for different purposes. That is
something we all have to simply accept. In that sense, there is no
point in writing down a hard and fast universally accepted definition.
Why do you wonder about whether or not I am defensive? Are you being
offensive? (just to be defensive, that latter is merely a supposedly
clever word inversion)
jillery
Feb 13, 2012, 5:35:36 AM2/13/12
to
On Sun, 12 Feb 2012 20:45:43 -0700, Richard Norman
<r_s_n...@comcast.net> wrote:
[...]
I don't say you're trying to write down a hard and fast defintion, nor
do I ask you to do so. So I don't understand why you argue a point I
didn't challenge.
>If people declare that evidence generally accepted by the scientific
>community is not really evidence then there is no point arguing with
>them on the basis of evidence.
Then that leaves one with few options. One can simply leave the
argument. Or one can continue the argument without evidence. ISTM
both are less than satisfactory solutions.
Of course, the point I raised isn't that some people declare
scientific evidence lacking, as you say above, but that they declare
their own evidence as *equivalent* to science's evidence. Big
difference. So I'm not sure how your conclusion above relates to the
situation I described.
>Why do you wonder about whether or not I am defensive?
Your apparently inappropriate "Live with it" and "silly argument"
comments, combined with your apparent unwillingness to acknowledge
them, and your attempts to change the subject.
>Are you being
>offensive? (just to be defensive, that latter is merely a supposedly
>clever word inversion)
I regret that you consider as being offensive my explicit efforts to
clearly understand what you think qualifies as credible speculation, a
topic you explicitly raised.
<r_s_n...@comcast.net> wrote:
[...]
do I ask you to do so. So I don't understand why you argue a point I
didn't challenge.
>If people declare that evidence generally accepted by the scientific
>community is not really evidence then there is no point arguing with
>them on the basis of evidence.
argument. Or one can continue the argument without evidence. ISTM
both are less than satisfactory solutions.
Of course, the point I raised isn't that some people declare
scientific evidence lacking, as you say above, but that they declare
their own evidence as *equivalent* to science's evidence. Big
difference. So I'm not sure how your conclusion above relates to the
situation I described.
>Why do you wonder about whether or not I am defensive?
comments, combined with your apparent unwillingness to acknowledge
them, and your attempts to change the subject.
>Are you being
>offensive? (just to be defensive, that latter is merely a supposedly
>clever word inversion)
clearly understand what you think qualifies as credible speculation, a
topic you explicitly raised.
Richard Norman
Feb 13, 2012, 9:52:07 AM2/13/12
to
On Mon, 13 Feb 2012 05:35:36 -0500, jillery <69jp...@gmail.com>
wrote:
I prefer to discuss zebra stripes.
wrote:
Burkhard
Feb 13, 2012, 10:22:59 AM2/13/12
to
On Feb 13, 2:52 pm, Richard Norman <r_s_nor...@comcast.net> wrote:
> On Mon, 13 Feb 2012 05:35:36 -0500, jillery <69jpi...@gmail.com>
They increase accidents for pedestrians, unless accompanied by
measures to slow down traffic, in which case they dramatically
decrease accident, making them rather ambiguous as far as natural
selection is concerned. That is not a just-so story, but supported by
very strong evidence. While the empirical facts are clear, their
metaphysical significance is hotly debates and some (Douglas Adams)
use them to argue that even if God did not exist, belief in him has
adaptionist advantages (such as being able to see Zebra stripes), or
something like that.
> On Mon, 13 Feb 2012 05:35:36 -0500, jillery <69jpi...@gmail.com>
measures to slow down traffic, in which case they dramatically
decrease accident, making them rather ambiguous as far as natural
selection is concerned. That is not a just-so story, but supported by
very strong evidence. While the empirical facts are clear, their
metaphysical significance is hotly debates and some (Douglas Adams)
use them to argue that even if God did not exist, belief in him has
adaptionist advantages (such as being able to see Zebra stripes), or
something like that.
Richard Norman
Feb 13, 2012, 11:09:09 AM2/13/12
to
be a just-so story, at least according to
http://www.alistapart.com/d/zebrastripingdoesithelp/zebra_striping_paper_21.pdf
jillery
Feb 13, 2012, 1:53:12 PM2/13/12
to
On Mon, 13 Feb 2012 07:52:07 -0700, Richard Norman
<r_s_n...@comcast.net> wrote:
>I prefer to discuss zebra stripes.
... but not what are credible speculations of same. Got it.
<r_s_n...@comcast.net> wrote:
>I prefer to discuss zebra stripes.
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