Re: [asa] Exaptation

From: Cameron Wybrow <>
Date: Tue Jun 23 2009 - 12:04:55 EDT

Bill and Randy:

I think these considerations regarding incrementalism are important. Of
course you both already know that even within the broadly Darwinian camp,
Gould had pointed out that the fossil record did not comport with Darwinian
gradualism. Michael Denton, in his first book, *Evolution: A Theory in
Crisis*, confirmed Gould's observations with reference to biochemistry,
pointing out that not only morphologically, but even with regard to certain
important proteins, the animal kingdom was characterized by gappiness and
clusters rather than gradualism and continuity, as classical neo-Darwinism
would predict.

I think that in Denton's second book, *Nature's Destiny* (which is not a
repudiation of the first book, as some suppose, but rather an attempt to go
beyond it), he suggests exactly what Bill is suggesting below, i.e., that
major changes in the phenotype could be built up by gradual changes in the
genotype. This would preserve Darwinian gradualism at the genetic level,
while explaining the discrepant phenomena observed by Gould, Denton and
others at the morphological and other levels. So Darwin would be both right
and wrong; right, in insisting upon gradualism, but wrong, in expecting that
all the gradual change would show up morphologically and be selected for.
Thus, Bill's remark about not necessarily being able to find transitional
species on the morphological level is quite a propos.

I see some problems with Denton's solution. He supposes (contra Darwin)
that most of the genetic changes aren't immediately expressed
morphologically or in any other way, but are "saved up", and then, when a
certain cluster of changes "makes sense", the whole cluster is expressed.
So genetic changes might accumulate over a million years, and then a new
creature might appear which would be quite different from its parents. It
would perhaps (though Denton doesn't say this; I'm just trying to make sense
of what he does say) look like a "hopeful monster" to the outsider, maybe, I
don't know, a bat born to a rodent mother (I'm making this example up;
Denton doesn't give any). But to the genetic observer over the
million-year-period, only gradualism would ever be seen: "random" looking
mutations. I have two tentative objections to this view: (a) how much
different could the offspring be from the parent, and survive? Particularly
in the case of mammals, who require maternal care after birth? Could a
bat-like creature, for example, still nurse from its rodent mother? Would
the milk, the nipples, etc. be compatible? More important, might the mother
not instinctively reject the freak child and refuse to nurse it? And even
in the case of reptiles, the mother crocodile carries around her tiny young
for a period in her mouth, to keep them safe; would she do so for some
(again, just a tentative example) some freak offspring that was hairy like a
mammal? (b) How does the genome know not to express the minor gradual
changes until they are all assembled? Why wouldn't it express each genetic
change right away? What internal mechanism "holds back" certain changes
from being expressed? Is there a timing mechanism of some kind? How would
it work? For Denton's theory to be correct, the operation of DNA must have
layers of sophistication that we have not yet fathomed. Of course that is
exactly his thesis, that the DNA is just part of the cosmic computer
program, so to speak, which was written before Creation and is meant to
"output" man. The question is, how do we go about confirming this
teleological aspect of the operation of DNA? Isn't such a view, while not
contradicted by the facts, at this point extremely speculative, and very

Hopefully Denton will address this question in his third book, which is due
out later this year.


----- Original Message -----
From: "Bill Powers" <>
To: "Randy Isaac" <>
Cc: <>
Sent: Tuesday, June 23, 2009 7:55 AM
Subject: Re: [asa] Exaptation

> Randy:
> I will try looking at some of the articles you reference.
> I take you to be saying that incrementalism on the genetic scale may
> produce "discontinuity" on the morphological scale.
> I suspected the same some 20 years ago when I first started studying
> evolutionary theory, which is why I thought at the time that we really
> don't know what a transitional species would look like.
> My experience with nonlinear and chaotic systems suggested to me that the
> same might be possible for biological systems.
> If this is the case, one ought to be at least suspect of any proposed
> transitional history since almost all are based upon morphological
> similarity, although I imagine the theory has begun to rely upon presumed
> ancestry.
> bill
> On Tue, 23 Jun 2009, Randy Isaac wrote:
>> Interesting point, Bill. I think we need to be careful about an argument
>> based on the a requirement of incrementalism. We still have so much to
>> learn about the quantization of descent with modification. In contrast to
>> Darwin's view of gradualism, the discovery of DNA led to a quantization
>> of changes at the molecular level but we still have so little awareness
>> of what that might mean macroscopically in the functional realm.
>> There have been several good articles in Science News recently that talk
>> about this. In January, an article showed some support for Conway
>> Morris's approach.
>> Molecular Evolution
>> Investigating the genetic books of life reveals new details of 'descent
>> with modification' and the forces driving it
>> By Tina Hesman Saey
>> January 31st, 2009; Vol.175 #3 (p. 26).
>> Even more relevant was a story in March on structure variants.
>> Jumping genes provide unexpected diversity
>> Mobile DNA elements help shape human genomes
>> By Tina Hesman Saey
>> March 14th, 2009; Vol.175 #6 (p. 16)
>> The above articles are too long to copy and post but most of you probably
>> have access to either paper or electronic copies.
>> The net is that incremental changes at the molecular level may be more
>> significant than we expected and the resulting functional impact may be
>> even greater.
>> Randy
>> ----- Original Message ----- From: "Bill Powers" <>
>> To: <>
>> Cc: <>
>> Sent: Tuesday, June 23, 2009 12:14 AM
>> Subject: [asa] Exaptation
>>> I'm continuing to think about Irreducible Complexity. A closely related
>>> concept is that of exaptation, wherein some biological structure or
>>> process
>>> used for one function is later used for a different function.
>>> Exaptation is apparently a well accepted doctrine and there a few
>>> carefully
>>> documented arguments to support the notion, including the development
>>> from the
>>> jaw bone for use in the middle ear, the bone spur of the panda
>>> developing into
>>> a thumb, and the development of feathers from thermal insulation into
>>> feathers
>>> for flight. The last two have problems in my mind conceptually, the
>>> first is
>>> perhaps the best.
>>> Nonetheless, exaptation appears to present theoretical problems, and
>>> here is why.
>>> It appears to me that Darwinian (random) evolution, not only presumes,
>>> but
>>> must be committed to a principle of incrementalism, whereby evolution
>>> sensibly
>>> proceeds according to small incremental changes.
>>> This principle appears necessary because of the random nature of the
>>> process.
>>> Significant, but random, changes are highly likely to be deadly,
>>> producing a
>>> non-survivable species. This is because it is likely that survival
>>> large
>>> changes are likely to be complex and highly integrated, but to expect a
>>> random
>>> process to be able to accomplish such a feat seems to ask far too much.
>>> On
>>> the other hand, small changes are more likely to leave the species still
>>> survivable. Such changes, while small, can be mildly advantageous,
>>> neutral,
>>> or even mildly disadvantageous.
>>> The principle of incrementalism presumes that in some sense that changes
>>> are
>>> near each other. But this nearness is not conceptual nearness,
>>> something
>>> utterly foreign to a blind process, but probablistic.
>>> Prima facie, exaptation violates this principle of incrementalism. This
>>> is so
>>> because the previous function is not probabilistically near the new
>>> function.
>>> It is conceptually near perhaps, but how can it be probabilistically
>>> near?
>>> Functionality is conceptual. I don't know how else to say it. In a
>>> sense the
>>> very notion of functionality is suspicious in a non-teleological
>>> process. But
>>> what then do we mean when we say in exaptation that an old function is
>>> used
>>> for a new one?
>>> To take, but one example, if one reviews, even in cartoon form the
>>> evolutionary development of the jaw bone into the middle ear, it appears
>>> to me
>>> to be miraculous if viewed as a random process. It only seems
>>> reasonable
>>> "conceptually," but not, to me, as a blind process.
>>> Can anyone help?
>>> thanks,
>>> bill
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Received on Tue Jun 23 12:08:49 2009

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