Hi all,
Interesting thread, but I have not had time to get involved. In any event, Darwin's Terrier has done a great job of presenting positions which I share with him. Just a few comments.
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pz:
The meaning is implicit in the word: an adaptation is a feature that is a consequence of selection acting on a population. It also implies something that improves the accommodation of an organism to its environment.
A feature that becomes fixed in a population by drift is not an adaptation unless it confers some selective advantage.
Darwin's Terrier:
Meanwhile, I'd say adaptation is the process of genetic change in a population over time (ie evolution), caused by natural selection, which means that the average version of a characteristic is improved ref what it does. (Therefore an adaptation is some feature that has become ‘standard issue' because it gives its owners a selective advantage in some way over those without it or with less good -- in relation to the environment at the time -- versions of it.)
It's a subset of ‘evolution' in general, the bit that causes improvement in function and therefore fitness. And hence, since selection is an ongoing process repeated algorithmically, adaptation is the process responsible for producing what I, at least , regard as all the interesting stuff: the organised complexity that cretinists bang on about : eyes, ears, wings, bacterial flagella and so on.
KC:
Maybe I'm just being perverse, but to me, even selectively neutral genes are adaptive, in the sense that they at least meet the minimal requirements of the environment at hand.
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In the glossary of Futuyma's
Evolutionary Biology, Third Edition, there is the following:
Quote:
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adaptation A process of genetic change of a population, owing to natural selection, whereby the average state of a character becomes improved with reference to a specific function, or whereby a population is thought to have become better suited to some feature of its environment. Also, an adaptation: a feature that has become prevalent in a population because of a selective advantage owing to its provision of an improvement in some function. A complex concept; see Chapter 12.
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(Chapter 12 is titled
Natural Selection and Adaptation, pp. 337-363) It is probably adaptations that most called for an explanation, which Darwin supplied. Traits that are not adaptive are also interesting, precisely because direct natural selection does not increase them in a population. Non-adaptive traits may be increased in a population due to natural selection acting on correlated traits, or simple genetic drift. Non-adaptive traits may also be found in a population even though they may be declining in frequency.
A lot has been made here about "pan-adaptionists", who apparently believe that all traits are adaptations, that selection always occurs at the level of the gene, and that evolution has always proceeded at a more or less constant and slow pace. Despite reading rather extensively on the subject (including peer-reviewed journal articles), I have never met, read about, or heard of even one such person. That is not to say that they don't exist, but they would certainly be exceptional and this does look like a "straw-man" argument. No evolutionary biologist that I have discussed such things with doubts that evolution has sometimes been rather rapid, sometimes almost stopped. There are, perhaps, a few who might think that all (or virtually all) traits are adaptive, but this would be a minority position (it would surprise me in any evolutionary biologist). I expect that you would find that most would accept that selection can and does occur at the level of the gene, but that selection at the level of the individual is what drives most evolution (selection at higher levels is generally accepted as being possible, but probably only rarely occurs because of certain constraints, research continues...). So, I am not sure what the fuss is all about.
Peez
01-29-2003, 01:05 PM
"pan-adaptionism" vs "naturalism"?
