[asa] Exaptation

From: Bill Powers <wjp@swcp.com>
Date: Tue Jun 23 2009 - 00:14:15 EDT

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?



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Received on Tue Jun 23 00:16:05 2009

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