Dawkins on Kimura



Larry Moran wrote:
> On Tue, 24 Feb 2004 20:57:28 +0000 (UTC), Anon. <[email protected]> wrote:
>
>>dkomo wrote:
>>
>>>Tim Tyler wrote:
>>
>
> [snip]
>
>
>>>>Drift may have something to say about small populations on islands around speciation events -
>>>>but it's probably a bit player in most other places - as far as the *features* of organisms go
>>>>(as opposed to the makeup of their genes).
>>>
>>>Really? You mean the fact that people have brown, green, or blue eyes, are short or tall, fat or
>>>skinny, beautiful or ugly, have red, black or blonde hair, are prone to get different diseases in
>>>old age, have different reactions to medications, have different physical abilities like being
>>>able to run for long distances, sing very well, be really strong, and so on and so on -- these
>>>are all the result of adaptations and natural selection?
>>>
>>
>>Why not? Their ancestors have experienced different environments, so hte selective pressures will
>>be different. Add into the mix variation in the environment (which can help maintain
>>polymorphism), and disruptive selection, we have plenty of adaptive explanations for the
>>diversity we see.
>>
>>Of course, drift may also be an explanation, but I believe that we can only separate out the
>>contributions of the different causes empirically.
>
>
> Yes. Until we can actually test the hypotheses it's wise not to *assume* that all morphological
> features are adaptations, don't you think?
>
As long as we can't exclude non-adaptive explanations, then we can't dismiss them. But there may be
occasions when making that assumption does lead to further enlightenment. It seems to be a problem
of scientific rhetoric.

Hmm. I'm not sure whether I answered you or not.

> Tim seems to be making the default assumption that most morphological features are due to natural
> selection. Dawkins certainly makes that assumption. Is this valid?
>
Well, it's valid. Is it correct? My feeling is that it is, but if someone show me evidence that it
isn't, then I'll change my mind.

Bob

--
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5) FIN-00014 University of Helsinki Finland Telephone: +358-9-191 23743
Mobile: +358 50 599 0540 Fax: +358-9-191 22 779 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal
of Negative Results - EEB: http://www.jnr-eeb.org
 
In article <[email protected]>,
Tim Tyler <[email protected]> wrote:
>Another quotable bit:
>
>``Darwinian selection remains the only explanation for adaptive evolution - and it is arguable (I
>would argue) that most if not all the evolutionary changes we actually see in the macroscopic world
>(as opposed to those concealed among the molecules) are adaptive and Darwinian.'' - A Devil's
>Chaplain, p.85.
>
>I'm not sure about the "all" but I'm inclined to agree with the "most".
>
>Drift may have something to say about small populations on islands around speciation events - but
>it's probably a bit player in most other places - as far as the *features* of organisms go (as
>opposed to the makeup of their genes).

Actually Dawkins's quote seems not to mention Kimura. And Kimura did not argue that visible
morphological characters "in the macroscopic world" were to be explained by neutral mutation. His
argument was about the bulk of change at the molecular level (which Dawkins calls changes "concealed
among the molecules"). He would have agreed that most of the visible morphological characters had
their adaptive change explained by natural selection. Kimura also allowed for many mutants being
eliminated owing to being deleterious.

So this thread is not discussing anything to do with Kimura.

--
Joe Felsenstein [email protected] Department of Genome Sciences and Department of
Biology, University of Washington, Box 357730, Seattle, WA 98195-7730 USA
 
Guy Hoelzer <[email protected]> wrote in message news:<[email protected]>...
> in article [email protected], Tim Tyler at [email protected] wrote on 2/23/04
> 7:53 PM:
>
> > Guy Hoelzer <[email protected]> wrote or quoted:
> >> in article [email protected], Tim Tyler at [email protected]
>
> >>> Another quotable bit:
> >>>
> >>> ``Darwinian selection remains the only explanation for adaptive evolution - and it is arguable
> >>> (I would argue) that most if not all the evolutionary changes we actually see in the
> >>> macroscopic world (as opposed to those concealed among the molecules) are adaptive and
> >>> Darwinian.'' - A Devil's Chaplain, p.85.
snip everything after opening quote except:

> > I guess that is true in theory - e.g. if you have a hypothetical system - where agents all
> > reproduce at the same rate - and have no phenotype and can't influence their own copying rate in
> > any way, then evolution will occur solely by drift. I'm not sure where Dawkins' views come in,
> > though.
>
> Right. This is all fine, but off the point and not what I meant to say. My point was that natural
> selection is not the only possible adaptive process.

what other adpative process is there? i understand that drift is useful for 'adaptive peaks and
valleys' and all, but even then its selection that is the over-riding factor. Or are you saying that
selection is merely not the only mechanism/force/player whatever involved?

snip
 
Jeffrey Turner wrote:
>
> Tim Tyler wrote:
>
> > Drift is most effective when population sizes are small. Selection is most effective when
> > population sizes are large. I reckon this fact (in conjunction with nature's population sizes)
> > will often limit's drift's usefulness as an explanation for features of organisms.
>
> What is "drift"? Genes mutate randomly, malign mutations die out, mutations that have no effect on
> an organism don't really matter and beneficial mutations propagate and supplant organisms without
> that mutation. This generally leads to a new species, in time. But what's "drift"?
>
> --Jeff
>

>From a post to talk.origins on Sept 5, 2002:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Subject: Neutral evolution simulation Date: Thu, 05 Sep 2002 13:21:25 -0600 From: dkomo
<[email protected]> Newsgroups: talk.orig

I ran across an interesting thought experiment that illustrates how neutral genes in a small
population can change frequencies due solely to sampling error/genetic drift. In other words, the
population can evolve even in the absence of any selection pressure.

Consider a jar full of 45 red marbles and 55 blue marbles. These represent the blue and red alleles
of a neutral gene. To simulate the fact that only a certain fraction of our marble "organisms" will
be able to reproduce (the rest will die or be unable to reproduce because of lack of food or water,
disease, etc.) select 50 marbles at random and throw them away. The remaining marbles in the jar are
allowed to reproduce by creating a copy of their allele, returning the size of the population back
to 100 marbles.

For example, let's say that in the 50 marbles selected, 20 were red and 30 were blue. The remaining
25 red marbles in the jar reproduce and so do the remaining 25 blue marbles. The jar now contains 50
red marbles and 50 blue marbles.

Repeat this experiment 100 times. At the end of the trials, which of these is correct:

1. The jar will contain 100 red marbles.
2. The jar will contain 100 blue marbles.
3. The jar will contain a mix of red and blue marbles in approximately the same ratio as it had
initially.
4. It's not possible to predict the marble ratios.
5. None of the above.
6. I don't know.
7. Who cares?

Note that if the number of either the red or blue marbles reaches 100, no further change is possible
because "mutations" are disallowed (red->blue, or blue->red during reproduction).

I'll post the answer a little latter.

[email protected]
 
Tim Tyler <[email protected]> wrote in message news:<[email protected]>...
> dkomo <[email protected]> wrote or quoted:
> > Tim Tyler wrote:
> > > dkomo <[email protected]> wrote or quoted:
> > > > Tim Tyler wrote:
snip
> > People who believe that most or all features of organisms have been selected for are known as
> > "panadaptationists."
>
> Genetic drift is enough to indicate than not all features of organisms have necessarily been
> selected for.
>
> Attributing "most" things to selection seems quite reasonable to me, though.
>
> > I was under the impression that panadaptationism is frowned upon these days by most
> > evolutionists.
>
> Adaptations are certainly all over the place.
>
> "Panadaptationism" is - or ought to mean "adaptations everywhere" - but exactly how common that is
> supposed to mean isn't clear.

seems to mean what you indicated it ought to mean, adaptations everywhere. Every trait is the result
of adaptation (or at least primarily/dominantly the result of adaptation). Seems to be an endpoint
on a spectrum. I can't imagine anyone is an acutal panadaptationist, but dawkin's certainly can
safely be refered to as one. How about Ultra-darwinian; seems to imply the same thing?
>
> The word doesn't seem to be in the dictionary - has anyone actually bothered to define it - or is
> it just a term of derision?

probably in as much as 'big bang' was intended to be insulting.
>
> > I think many of the traits I pointed out are either what Gould called "spandrels":
> >
> > http://spandrel.com/about.html
> >
> > or they are neutral mutations that have persisted within human populations for a very long time.
> > They are *not* adaptations to anything.
>
> Most of your traits were statements about the existence of variation within in a trait.
>
> You mentioned: brown, green, or blue eyes, being short or tall, being fat or skinny, being
> beautiful or ugly, having red, black or blonde hair - and so on.
>
> I've discussed eye colour already. Height is an adaptive trait - perhaps with some frequency
> dependent selection for different heights being caused by the existence of different
> lifestyles. Similarly with weight. Also, a fair bit of the observed variation in both traits is
> not genetic at all.
>
> Beauty is adaptive - and being ugly is mal-adaptive - and exists through being constantly
> generated - and not yet having been weeded out. Hair colour is also adaptive. Black hair protects
> against UV radiation - and that's why all African types have black hair (except a few albinos who
> soon get ill). Red and blond hair are (I claim) clearly the result

>

but certainly you wouldn't claim that all traits are adaptive. As far as the 'major' features
of evolution being adaptive, well thats a different story and i think its what you mean by
'most' traits.

> > > * there is such a thing as frequency-dependent selection;
> > > * most of the members of the population will not be long-term ancestors - and any variation
> > > they exhibit is of pretty low relevance;
> > >
> > > The second point grows in force when you take a gene's eye view.
> > >
> > > Of your examples, I would identify the best one as "eye colour".
> > >
> > > There /may/ be a case that eye colour is the subject of drift.
> >
> > Why does it have to be the subject of drift? It could simply be an allele which is not under
> > selection and whose frequency remains pretty constant in a particular human subpopulation.
>
> If the population is finite, it will drift.
>
also, how is an allele not subject to selection -not- going to drift?

> > > ***If*** so, eye colour would be one of the things I classified as a "minor feature".
> > >
> > > However I am not convinced that eye colour is anywhere remotely *near* neutral.
> > >

> > > existence of variation in it can be explained adaptively by the hypothesis that those with
> > > unusual iris colours tend to be preferred mates.
> > >
> > > Further, there is geographic variation in the trait - which suggests to me adaptation as a sun-
> > > shield.
> > >
> > > If eye colour is *not* significantly under the influence of selection, how come nature has
> > > chosen bright pure pigments for the irises of the eyes of many people's in northern regions -
> > > while ensuring a hefty dark melanin pigment in those whose ancestors lived closest to the
> > > equator and were most exposed to the sun?
> > >

I'll just respond to this here instead of in the original post. ettiqute schmettiquite.

i think the dark eye colour can be considered the default. As far as bright eye colour, even if all
northern pops had this trait (say blue in one pop, green in another, but i don't think this is even
strictly true) then why green in one and blue in the other? Either way it seems historical
accident/constraint is going to be involved. Except

issue, not completly but something different anyways.

> > > In summary, I think there are plenty of signs that iris colouration is strongly adaptive.
> >
> > It could be. I'm not the diametric opposite of a panadaptationist, as one well known poster to
> > this group is, but I do insist that the burden of proof lies with those who claim that
> > particular traits are adaptations.
>
> Hmm. It seems to me that whenever I get into a discussion there's always someone who claims that
> the burden of proof lies on my side.
>
> Nine times out of ten I can't see why that is the case - and this is one of them.
>
> I suggest "adaptation" should *normally* be the default hypothesis - because adaptation has shown
> itself to be the best, most powerful theory for accounting for the forms of organisms.
>
> That's not to say that it's responsible for *everything* - but that - if anything - the burden of
> proof ought to normally be on the drift side of the fence - since drift typically hasn't been
> shown to be responsible for very much of anything.
>

how about no default either way?

> > You made an argument about eye color, but you don't have any empirical proof.
>
> ...but I could soon find some on request. The dark eyes of african populations is a well known
> fact - and has no explanation under the hypothesis that iris colour is subject to drift.
>

why would the eye colour change simply because of drift tho? If it was, then one could look at say
pops where dark eyes are dominant, put corrective surgery and glasses (heck even sunglasses) and
whatnot eliminates whatever advantage dark eyes might've had formerly. Do those pops show evidence
torwards more variation in eye colour? If not, well there wouldn't be much info there, but if they
did, that would be interesting.

snip
 
On Thu, 26 Feb 2004 16:44:29 +0000 (UTC),
Anon. <[email protected]> wrote:
> dkomo wrote:

[snip]

>> We have plenty of "just so" stories to explain each and every purported adaptation. Any amateur
>> evolution theorist can come up with half a dozen armchair explanations for each such trait. What
>> we don't have in most cases is empirical proof that a particular feature of an organisn is indeed
>> an adaptation to the environment.
>>
> Yes, so we need empirical observation to resolve this argument. My point is that we know that
> spatial and temporal variation in selection pressures occurs, so we can't rule them out just
> because we don't like them.

Right. We also know for a fact that random genetic drift occurs so you can't rule it out just
because you don't like it.

> Examining their effects is difficult (I've looked at both. One study needed a 60 year time seies,
> the other merely a crossing experiment with a couple of thousand frogs).

Nobody said it was easy to prove natural selection or random genetic drift. The key point to keep in
mind is that in the absence of proof for one mechanism or another you have to keep an open mind and
not just assume that it's your favorite mechanism that works.

It's easy to make up "just-so" adaptionist stories. The tricky part is realizing that they are just
stories and not real explanations.

>>>Of course, drift may also be an explanation, but I believe that we can only separate out the
>>>contributions of the different causes empirically.
>>
>> It may be that many features of organisms are incidental and play no role in their evolution.
>> That doesn't necessarily imply that these features are subject to drift.

If the features are not adaptive then they must be neutral (or nearly neutral). If the aleles for
these features are neutral with respect to fitness than there frequency in the population *will* be
subject to random genetic drift. You can't stop it.

>> Drift is a phenomenon of small, isolated populations.

This is an incorrect statement.

> And there are a lot of them about, even in organisms like insects.

Exactly right. In the real world it's almost impossible to have a large population of randomly
mating individuals (i.e., panmitic). Almost any population that you can think of is subdivided into
a large number of much smaller sub-populations that are more-or-less genetically isolated from each
other. This is obvious in humans but it's true of every other species as well.

Larry Moran
 
On Thu, 26 Feb 2004 16:44:30 +0000 (UTC),
Anon. <[email protected]> wrote:
> Larry Moran wrote:
>> On Tue, 24 Feb 2004 20:57:28 +0000 (UTC), Anon. <[email protected]> wrote:
>>>dkomo wrote:
>>>>Tim Tyler wrote:

[snip]

>>>Of course, drift may also be an explanation, but I believe that we can only separate out the
>>>contributions of the different causes empirically.
>>
>> Yes. Until we can actually test the hypotheses it's wise not to *assume* that all morphological
>> features are adaptations, don't you think?
>>
> As long as we can't exclude non-adaptive explanations, then we can't dismiss them. But there may
> be occasions when making that assumption does lead to further enlightenment. It seems to be a
> problem of scientific rhetoric.
>
> Hmm. I'm not sure whether I answered you or not.

Yes, you've helped me to understand your point of view. :)

>> Tim seems to be making the default assumption that most morphological features are due to natural
>> selection. Dawkins certainly makes that assumption. Is this valid?
>>
> Well, it's valid. Is it correct? My feeling is that it is, but if someone show me evidence that it
> isn't, then I'll change my mind.

I can understand your "feeling." Since we don't have very good evidence one way of the other is it
valid science to rely on "feeling"? Why are you asking for experimental evidence against your
feeling? I could just as easily state that most features are due to drift and it's up to you to
prove otherwise. Would that be an example of good science?

Why don't we just say that morphological features can become fixed in a population by adaptation -
and quote some known expamples. We don't know if *most* morphological features are due to adaptation
or whether they are accidents of evolution.

Larry Moran
 
What role do neutral mutations play in evolution? One reads about genetic drift and how much the
immense genetic variety is due to neutral mutations and inconsequential to survival and
reproduction. Afterall, a neutral mutation is a mutation which results in a change of the genotype
without changing the phenotype or associated fitness value. Or this this too simplistic a definition
of neutral mutation?

The role of neutral mutations are stressed in the theory of punctuated equilibrium. As Gould
maintained this theory was never intended to replace Darwinian gradualism but rather to add to it.
According to the theory if enough "beneficial neutral mutations e.g. a combination which is
beneficial and reaches a certain theshold..it can result in an episode of punctuated eqilibrium or
speciation. Such an event doesn't represent a major transition from one organism to another but
rather "little jumps".

My question is if enough neutral mutations accumulated which resulted in some beneficial
combination...wouldn't natural selection then act? What determines that a particular accumulation of
neutral mutations is beneficial?

Michael Ragland
 
[email protected] wrote or quoted:
> Tim Tyler <[email protected]> wrote:

> >Another quotable bit:
> >
> >``Darwinian selection remains the only explanation for adaptive evolution - and it is arguable (I
> >would argue) that most if not all the evolutionary changes we actually see in the macroscopic
> >world (as opposed to those concealed among the molecules) are adaptive and Darwinian.'' - A
> >Devil's Chaplain, p.85.

[...]

> Actually Dawkins's quote seems not to mention Kimura. And Kimura did not argue that visible
> morphological characters "in the macroscopic world" were to be explained by neutral mutation. His
> argument was about the bulk of change at the molecular level (which Dawkins calls changes
> "concealed among the molecules"). He would have agreed that most of the visible morphological
> characters had their adaptive change explained by natural selection. Kimura also allowed for many
> mutants being eliminated owing to being deleterious.
>
> So this thread is not discussing anything to do with Kimura.

To explain/justify my subject line, I'll add a little bit to the quote - fair use permitting ;-):

``The only point of controversy introduced by Kimura is how many mutations are neutral. Kimura
thought it was the great majority which, if true, is very nice for the molecular clock. Darwinian
selection remains the only explanation for adaptive evolution - and it is arguable (I would argue)
that most if not all the evolutionary changes we actually see in the macroscopic world (as opposed
to those concealed among the molecules) are adaptive and Darwinian.'' - A Devil's Chaplain, p.85.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove lock to reply.
 
[email protected] (Larry Moran) wrote in
news:[email protected]:

> On Tue, 24 Feb 2004 20:57:28 +0000 (UTC), Anon. <[email protected]> wrote:
>> dkomo wrote:
>>> Tim Tyler wrote:
>
> [snip]
>
>>>>Drift may have something to say about small populations on islands around speciation events -
>>>>but it's probably a bit player in most other places - as far as the *features* of organisms go
>>>>(as opposed to the makeup of their genes).

>>> Really? You mean the fact that people have brown, green, or blue eyes, are short or tall, fat or
>>> skinny, beautiful or ugly, have red, black or blonde hair, are prone to get different diseases
>>> in old age, have different reactions to medications, have different physical abilities like
>>> being able to run for long distances, sing very well, be really strong, and so on and so on --
>>> these are all the result of adaptations and natural selection?

>> Why not? Their ancestors have experienced different environments, so hte selective pressures will
>> be different. Add into the mix variation in the environment (which can help maintain
>> polymorphism), and disruptive selection, we have plenty of adaptive explanations for the
>> diversity we see.

>> Of course, drift may also be an explanation, but I believe that we can only separate out the
>> contributions of the different causes empirically.

> Yes. Until we can actually test the hypotheses it's wise not to *assume* that all morphological
> features are adaptations, don't you think?
>
> Tim seems to be making the default assumption that most morphological features are due to natural
> selection. Dawkins certainly makes that assumption. Is this valid?

Haven't we had this debate before on sbe? I believe it was termed at that time the "null hypothesis"
rather than the "default assumption". My personal opinion, FWIW, is that we can make a good first
guess about a trait without the need for a default.

If the trait shows little variation throughout a large population or is strongly correlated with an
obvious environmental variable, and has an obvious relation to an aspect of species behavior, one
can make the default assumption that it is an adaptation, especially if it has existed for a long
period.(Again based on recollection, Wirt did a much better job than I just did of defining what
traits could be considered adaptive as a default). Examples would include large ears in elephants,
skin color in humans, and almost any morphological feature of horseshoe crabs.

If the trait shows wide variation throughout a population regardless of environmental variables, or
is confined to isolated subpopulations with no obvious relation to fitness, one can make the default
assumption that it is due to drift. Examples include coat color in domestic cats and the Rh- blood
type in humans.

Note that I am cheating somewhat, as I am assuming there is at least some data available to make a
"default" assumption. Also, the above _are_ only default assumptions - either may be proved false by
better data, so ultimately I agree with Bob. Also note that there will be a lot of traits -
morphological features and otherwise - that will not fall into either category. In this case the
adaptationists (including myself) will dream up unsubstantiated Just So stories to which the
drifters (sorry - the term has both a nice slightly pejorative ring to my ears as well as reminding
me of the 60's rock band) will recoil in horror :)

Yours,

Bill Morse
 
in article [email protected], R.Schenck at
[email protected] wrote on 2/27/04 8:40 AM:

> Guy Hoelzer <[email protected]> wrote in message news:<[email protected]>...
>> in article [email protected], Tim Tyler at [email protected] wrote on 2/23/04
>> 7:53 PM:
>>
>>> Guy Hoelzer <[email protected]> wrote or quoted:
>>>> in article [email protected], Tim Tyler at [email protected]
>>
>>>>> Another quotable bit:
>>>>>
>>>>> ``Darwinian selection remains the only explanation for adaptive evolution - and it is arguable
>>>>> (I would argue) that most if not all the evolutionary changes we actually see in the
>>>>> macroscopic world (as opposed to those concealed among the molecules) are adaptive and
>>>>> Darwinian.'' - A Devil's Chaplain, p.85.
> snip everything after opening quote except:
>
>>> I guess that is true in theory - e.g. if you have a hypothetical system - where agents all
>>> reproduce at the same rate - and have no phenotype and can't influence their own copying rate in
>>> any way, then evolution will occur solely by drift. I'm not sure where Dawkins' views come in,
>>> though.
>>
>> Right. This is all fine, but off the point and not what I meant to say. My point was that natural
>> selection is not the only possible adaptive process.
>
> what other adpative process is there? i understand that drift is useful for 'adaptive peaks and
> valleys' and all, but even then its selection that is the over-riding factor. Or are you saying
> that selection is merely not the only mechanism/force/player whatever involved?

I am saying something roughly like your last alternative. I think that the evidence is now
overwhelming, and mostly overlooked by evolutionary biologists, that natural selection is a
particular form of more general (thermodynamic) set of optimizing, adaptive processes. Biology
specializes on natural selection as an adaptive process, but there is no reason that others kinds of
adaptive mechanisms can't also participate in causing adaptive evolution.

Guy
 
Larry Moran <[email protected]> wrote or quoted:

> I can understand your "feeling." Since we don't have very good evidence one way of the other is it
> valid science to rely on "feeling"? Why are you asking for experimental evidence against your
> feeling? I could just as easily state that most features are due to drift and it's up to you to
> prove otherwise. Would that be an example of good science?
>
> Why don't we just say that morphological features can become fixed in a population by adaptation -
> and quote some known expamples. We don't know if *most* morphological features are due to
> adaptation or whether they are accidents of evolution.

Simon Conway Morris's latest book bears on this question:

``Life's Solution : Inevitable Humans in a Lonely Universe''

It suggests that evolution has designed functionally the *same* structure from *different* starting
points - in a very large number of cases.

He gives quite a few good examples of this convergent evolution.

It is easily explicable on the assumption that "most features" of organisms were adaptations - but
would be puzzling if they were accidents.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove lock to reply.
 
R.Schenck <[email protected]> wrote or quoted:
> Tim Tyler <[email protected]> wrote in message news:<[email protected]>...
> > dkomo <[email protected]> wrote or quoted:

> > > I was under the impression that panadaptationism is frowned upon these days by most
> > > evolutionists.
> >
> > Adaptations are certainly all over the place.
> >
> > "Panadaptationism" is - or ought to mean "adaptations everywhere" - but exactly how common that
> > is supposed to mean isn't clear.
>
> seems to mean what you indicated it ought to mean, adaptations everywhere.

In which case the term is next to useless - nobody believes that:

``No Darwinian from Darwin on has expected that every possible feature would be adaptive, and so
panadaptationism is a strawman''

- http://www.users.bigpond.com/thewilkins/papers/Neplusultra.html

> Every trait is the result of adaptation (or at least primarily/dominantly the result of
> adaptation). Seems to be an endpoint on a spectrum. I can't imagine anyone is an acutal
> panadaptationist, but dawkin's certainly can safely be refered to as one.

``Most if not all of the evolutionary changes we see in the macroscopic world [...] are adaptive and
Darwinian.'' - p.85.

- "The Devil's Chaplain".

It seem's like he's avoided being a panadaptationist here - since his wording avoids going for the
"all" option.

Close - but no cigar, I reckon.

> > The word doesn't seem to be in the dictionary - has anyone actually bothered to define it - or
> > is it just a term of derision?
>
> probably in as much as 'big bang' was intended to be insulting.

Wasn't the term coined by Lewontin and Gould, though? I don't believe a compliment was intended.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove lock to reply.
 
Larry Moran wrote:
> On Thu, 26 Feb 2004 16:44:30 +0000 (UTC), Anon. <[email protected]> wrote:
>
<snip>
>>>Tim seems to be making the default assumption that most morphological features are due to natural
>>>selection. Dawkins certainly makes that assumption. Is this valid?
>>>
>>
>>Well, it's valid. Is it correct? My feeling is that it is, but if someone show me evidence that it
>>isn't, then I'll change my mind.
>
>
> I can understand your "feeling." Since we don't have very good evidence one way of the other is it
> valid science to rely on "feeling"? Why are you asking for experimental evidence against your
> feeling? I could just as easily state that most features are due to drift and it's up to you to
> prove otherwise. Would that be an example of good science?
>
> Why don't we just say that morphological features can become fixed in a population by adaptation -
> and quote some known expamples. We don't know if *most* morphological features are due to
> adaptation or whether they are accidents of evolution.
>
The problem with that is that it seems unlikely that most traits will have become fixed, because
most traits have a function. If you're saying that they became fixed by drift, then you're invoking
a rather strange form of the blind watchmaker.

Bob

--
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5) FIN-00014 University of Helsinki Finland Telephone: +358-9-191 23743
Mobile: +358 50 599 0540 Fax: +358-9-191 22 779 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal
of Negative Results - EEB: http://www.jnr-eeb.org
 
William Morse <[email protected]> wrote or quoted:

> If the trait shows little variation throughout a large population or is strongly correlated with
> an obvious environmental variable, and has an obvious relation to an aspect of species behavior,
> one can make the default assumption that it is an adaptation, especially if it has existed for a
> long period.(Again based on recollection, Wirt did a much better job than I just did of defining
> what traits could be considered adaptive as a default). Examples would include large ears in
> elephants, skin color in humans, and almost any morphological feature of horseshoe crabs.
>
> If the trait shows wide variation throughout a population regardless of environmental variables,
> or is confined to isolated subpopulations with no obvious relation to fitness, one can make the
> default assumption that it is due to drift. Examples include coat color in domestic cats and the
> Rh- blood type in humans.

Genes for traits can reach fixation by accident in small populations.

They can remain fixed due to selective lock-in if other adaptations come to depend on
their presence.

Old, non-variable traits (of any sort) need not /necessarily/ represent adaptations.

Incidentally, are you /really/ suggesting a human blood type is neutral? Are not blood types often
critical in disease resistance? That is surely a case of parasite-driven selection favouring
diversity.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove lock to reply.
 
dkomo wrote:
> Jeffrey Turner wrote:
>>Tim Tyler wrote:
>>
>>
>>>Drift is most effective when population sizes are small. Selection is most effective when
>>>population sizes are large. I reckon this fact (in conjunction with nature's population sizes)
>>>will often limit's drift's usefulness as an explanation for features of organisms.
>>
>>What is "drift"? Genes mutate randomly, malign mutations die out, mutations that have no effect on
>>an organism don't really matter and beneficial mutations propagate and supplant organisms without
>>that mutation. This generally leads to a new species, in time. But what's "drift"?
>
>
>>From a post to talk.origins on Sept 5, 2002:
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Subject: Neutral evolution simulation Date: Thu, 05 Sep 2002 13:21:25 -0600 From: dkomo
> <[email protected]> Newsgroups: talk.orig
>
> I ran across an interesting thought experiment that illustrates how neutral genes in a small
> population can change frequencies due solely to sampling error/genetic drift. In other words, the
> population can evolve even in the absence of any selection pressure.
>
> Consider a jar full of 45 red marbles and 55 blue marbles. These represent the blue and red
> alleles of a neutral gene. To simulate the fact that only a certain fraction of our marble
> "organisms" will be able to reproduce (the rest will die or be unable to reproduce because of lack
> of food or water, disease, etc.) select 50 marbles at random and throw them away. The remaining
> marbles in the jar are allowed to reproduce by creating a copy of their allele, returning the size
> of the population back to 100 marbles.
>
> For example, let's say that in the 50 marbles selected, 20 were red and 30 were blue. The
> remaining 25 red marbles in the jar reproduce and so do the remaining 25 blue marbles. The jar now
> contains 50 red marbles and 50 blue marbles.
>
> Repeat this experiment 100 times. At the end of the trials, which of these is correct:
>
> 1. The jar will contain 100 red marbles.
> 2. The jar will contain 100 blue marbles.
> 3. The jar will contain a mix of red and blue marbles in approximately the same ratio as it had
> initially.
> 4. It's not possible to predict the marble ratios.
> 5. None of the above.
> 6. I don't know.
> 7. Who cares?
>
> Note that if the number of either the red or blue marbles reaches 100, no further change is
> possible because "mutations" are disallowed (red->blue, or blue->red during reproduction).

Off-hand, I'd say 3 is probably correct. There is a finite probability of any other distribution,
however. Is one hundred individuals a realistic population? It seems very small, and the odds of any
appreciable "drift" decrease dramatically as population size increases. So, it seems to me, drift
may be conceptualizable but it won't be a significant phenomenon. As for how any significant
"deviant" population would arise in the first place without selection, it must either have arisen by
mutation or been inherited early in the history of a species _or_ occurred as a fairly regular
mutation in a well established species.

From an evolutionary standpoint, the most realistic answer is 7.

--Jeff

--
A man, a plan, a cat, a canal - Panama!

Ho, ho, ho, hee, hee, hee and a couple of ha, ha, has; That's how we pass the day away, in the merry
old land of Oz.
 
On Sat, 28 Feb 2004 18:18:20 +0000 (UTC),
William Morse <[email protected]> wrote:
> [email protected] (Larry Moran) wrote in news:[email protected]:

[snip]

>> Tim seems to be making the default assumption that most morphological features are due to natural
>> selection. Dawkins certainly makes that assumption. Is this valid?
>
> Haven't we had this debate before on sbe? I believe it was termed at that time the "null
> hypothesis" rather than the "default assumption". My personal opinion, FWIW, is that we can make a
> good first guess about a trait without the need for a default.

Yes, I think we've debated this before on sbe. :)

Is there a rule about not bringing up the same topic again? It seems to me that there are a some
topics that seem to be "debated" over and over again on this newsgroup so I assumed that this
was okay. :)

Seriously, I think it's more interesting to discuss adaptionism and random genetic drift than some
of the other things that are taking up time on sbe. Do you agree?

> If the trait shows little variation throughout a large population or is strongly correlated with
> an obvious environmental variable, and has an obvious relation to an aspect of species behavior,
> one can make the default assumption that it is an adaptation, especially if it has existed for a
> long period.(Again based on recollection, Wirt did a much better job than I just did of defining
> what traits could be considered adaptive as a default). Examples would include large ears in
> elephants, skin color in humans, and almost any morphological feature of horseshoe crabs.
>
> If the trait shows wide variation throughout a population regardless of environmental variables,
> or is confined to isolated subpopulations with no obvious relation to fitness, one can make the
> default assumption that it is due to drift. Examples include coat color in domestic cats and the
> Rh- blood type in humans.

Hmmmm .... I would have thought that ear size in elephants and skin color in humans were excellent
example of drift. Don't you see how difficult it is to make general rules? Your decision about what
the "default" hypothesis should be depends to a great extent on your original biases. This is
exactly the point that Lewontin and Gould made in their original paper. If you tend to emphasize
natural selection in your thinking about evolution then you will look to adaptive explanations ahead
of non-adaptive explanations.

> Note that I am cheating somewhat, as I am assuming there is at least some data available to make a
> "default" assumption.

Part of the problem is that even the selection of "data" has built-in biases. If you are an
adaptionist, and you prefer an adaptionist explanation, then you go looking for data to support your
assumption. For example, if you think human skin color is adaptive then the only "data" you quote is
the little bit that might explains why people with white skin lived in Northern Europe.

> Also, the above _are_ only default assumptions - either may be proved false by better data, so
> ultimately I agree with Bob. Also note that there will be a lot of traits - morphological features
> and otherwise - that will not fall into either category. In this case the adaptationists
> (including myself) will dream up unsubstantiated Just So stories to which the drifters (sorry -
> the term has both a nice slightly pejorative ring to my ears as well as reminding me of the 60's
> rock band) will recoil in horror :)

No offense. I'm a drifter in the sense that it's part of my self-proclaimed "mission" to educate
people about the importance of random genetic drift and evolution by accident. I'm not having much
luck on sci.bio.evolution. This newsgroup is heavily dominated by people who reject the very concept
of drift or who have deliberately chosen not to understand it. I find this very strange in a
newsgroup that's supposed to be devoted to discussing evolution at a serious level.

Larry Moran
 
William Morse wrote:
>

> Note that I am cheating somewhat, as I am assuming there is at least some data available to make a
> "default" assumption. Also, the above _are_ only default assumptions - either may be proved false
> by better data, so ultimately I agree with Bob. Also note that there will be a lot of traits -
> morphological features and otherwise - that will not fall into either category. In this case the
> adaptationists (including myself) will dream up unsubstantiated Just So stories to which the
> drifters (sorry - the term has both a nice slightly pejorative ring to my ears as well as
> reminding me of the 60's rock band) will recoil in horror :)
>

Right. As far as I can tell, Gould's spandrels don't fall into either category. These are incidental
traits produced as side-effects of the overall morphology of an organism. Spandrels are not
adaptations nor do they result from genetic drift.

[email protected]
 
Guy Hoelzer <[email protected]> wrote or quoted:
> in article [email protected], R.Schenck at
> > Guy Hoelzer <[email protected]> wrote in message

> >> My point was that natural selection is not the only possible adaptive process.
> >
> > what other adpative process is there? i understand that drift is useful for 'adaptive peaks and
> > valleys' and all, but even then its selection that is the over-riding factor. Or are you saying
> > that selection is merely not the only mechanism/force/player whatever involved?
>
> I am saying something roughly like your last alternative. I think that the evidence is now
> overwhelming, and mostly overlooked by evolutionary biologists, that natural selection is a
> particular form of more general (thermodynamic) set of optimizing, adaptive processes.

I.e. self-organising systems.

> Biology specializes on natural selection as an adaptive process, but there is no reason that
> others kinds of adaptive mechanisms can't also participate in causing adaptive evolution.

I'm sure they do.

To take a simple example, I think the human brain is /heavily/ influenced by "self-organising"
mechanisms during its development.

Speaking /very/ crudely, I think the genome says something like: make lots of these neuron things,
according to these rules, wire them together with these sensors and these motor units - and then let
them get on with things.

The resulting adult brain thus owes a great deal to self-organising processes.

Such processes can influence gene frequencies via selection and the Baldwin effect.

Having said that, natural selection is /still/ pretty fundamental.

Since it gets to decide which self-organising systems exist and which don't, it pretty-much has the
final word.

In the future we will see completely new ways for adaptions to arise in organisms - namely they will
be designed and engineered to be there - the products of "mutations" directed by intelligent design
- but even then, natural selection will still preside over everything.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove lock to reply.
 
Guy Hoelzer <[email protected]> wrote in message news:<[email protected]>...
> in article [email protected], R.Schenck at [email protected] wrote on
> 2/27/04 8:40 AM:
>
> > Guy Hoelzer <[email protected]> wrote in message news:<[email protected]>...
> >> in article [email protected], Tim Tyler at [email protected] wrote on 2/23/04
> >> 7:53 PM:
> >>
> >>> Guy Hoelzer <[email protected]> wrote or quoted:
> >>>> in article [email protected], Tim Tyler at [email protected]
>
> >>>>> Another quotable bit:
> >>>>>
> >>>>> ``Darwinian selection remains the only explanation for adaptive evolution - and it is
> >>>>> arguable (I would argue) that most if not all the evolutionary changes we actually see in
> >>>>> the macroscopic world (as opposed to those concealed among the molecules) are adaptive and
> >>>>> Darwinian.'' - A Devil's Chaplain, p.85.
> > snip everything after opening quote except:
> >
> >>> I guess that is true in theory - e.g. if you have a hypothetical system - where agents all
> >>> reproduce at the same rate - and have no phenotype and can't influence their own copying rate
> >>> in any way, then evolution will occur solely by drift. I'm not sure where Dawkins' views come
> >>> in, though.
> >>
> >> Right. This is all fine, but off the point and not what I meant to say. My point was that
> >> natural selection is not the only possible adaptive process.
> >
> > what other adpative process is there? i understand that drift is useful for 'adaptive peaks and
> > valleys' and all, but even then its selection that is the over-riding factor. Or are you saying
> > that selection is merely not the only mechanism/force/player whatever involved?
>
> I am saying something roughly like your last alternative. I think that the evidence is now
> overwhelming, and mostly overlooked by evolutionary biologists, that natural selection is a
> particular form of more general (thermodynamic) set of optimizing, adaptive processes. Biology
> specializes on natural selection as an adaptive process, but there is no reason that others kinds
> of adaptive mechanisms can't also participate in causing adaptive evolution.
i am curious about this, what other mechanisms lead to adaption besides nat select. ? I understand
that other mechanims are involved in evolution, but not that they necessarily lead to adapatations,
whereas natural selection 'selects' for adapatations. So what are these other mechanisms that select
adapations? I guess i don't expect a full explanation here, but what texts go into it at least? I
probably shouldn't be asking for -more- stuff to read now, but at least i could add it to the list.
 
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