Re: [asa] Exaptation

From: Bill Powers <wjp@swcp.com>
Date: Tue Jun 23 2009 - 07:55:32 EDT

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.
> http://www.sciencenews.org/view/feature/id/40006/title/Molecular_Evolution
> 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.
> http://www.sciencenews.org/view/generic/id/40922/title/Jumping_genes_provide_unexpected_diversity
> 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" <wjp@swcp.com>
> To: <asa@calvin.edu>
> Cc: <wjp@swcp.com>
> 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 07:56:13 2009

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