Re: [asa] Exaptation

From: Jim Armstrong <>
Date: Tue Jun 23 2009 - 20:44:54 EDT

When language like incrementalism and gradualism are in play, there is
an accompanying sense that evolutionary "progress" is akin to inchworm
progress. While that may be true in the long term, within the last year
(or so), there have been headlines to the effect that there is great
variability in the impact of a given mutation, in particular making room
for evolutionary steps that are rather large in net effect.

With respect to a common put that most mutations are likely to be fatal,
I don't know that this is established at all, just plausible perception.
But all these arguments pro and con have been offered elsewhere. I would
just observe that a fatal mutation is a large impact indeed, not
anything resembling an inchworm "step".

JimA [Friend of ASA]

Cameron Wybrow wrote:
> 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 problematic?
> Hopefully Denton will address this question in his third book, which
> is due out later this year.
> Cameron.
> ----- 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 20:46:02 2009

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