Re: Evolution, "adaptation", and what's currently adaptive
Stephen Barnard (steve@megafauna.com)
Sat, 31 Aug 1996 14:44:42 -0800
Susan S. Chin wrote:
>
> Stephen Barnard (steve@megafauna.com) wrote:
> : Susan S. Chin wrote:
> : > My understanding of Gould's critique of adaptationists can be related to
> : > his concept, presented with Elisabeth Vrba in 1982, of "exaptations."
> : > Anyone familiar with this concept knows that it refers to characters which
> : > currently may serve an "adaptive" function, but did not arise and evolve
> : > via natural selection for the current utility. Their point being that
> : > just because something is functionally significant today, does not mean
> : > that the feature originated and was shaped by selective pressures, or
> : > "natural selection."
>
> : I very much doubt that Bryant would find much, if anything, to quarrel about with
> : the "exaptation" notion. This is actually a pure adaptationist idea.
>
> Thanks for your opinion Steve. But I was actually only addressing the
> discussions preceding this, which I don't believe you were a part of.
If you want to conduct a private discussion with Len and Bryant then you can use
email. If you post an opinion publicly then I feel that I and anyone else has a
right to comment on it.
> But
> now that you've given your opinion of Bryant's position, what exactly do
> you mean by exaptation "is actually a pure adaptationist idea"? Care to
> elaborate?
So-called "exaptation" (if Gould is good at nothing else, he's good at coining catchy
phrases) has long been a part of the neo-Darwinian adaptationist framework. One of
the most well-known examples is the bones of the inner ear of mammals, which were
"exapted" from the bones of the reptilian jaw. One consequence is that mammals have
much better ears than reptiles, but fewer bones in their jaws. This probably
forecloses the possibility of a mammal ever being able to swallow something much
larger than it's head, as snakes commonly do.
>
> : My problem with Gould and Lewontin is that their argument proceeds by carefully
> : setting up a straw man (The Panglossian adaptationist), and then knocking the
> : stuffing out it. Their paper has been seized upon by many people who, for one
> : reason or another, don't want to accept the notion of evolution through natural
> : selection. "Look, even the famous Stephen J. Gould says that evolution is bunk!"
>
> I don't think that was what the thread of this discussion was about. From
> what I can tell, neither Bryant nor Len thinks this obviously. But
> rather, why should every feature that exists today "have" to have some
> adaptive or fitness value? That is the adaptationist view as I know it.
> What's yours?
This is exactly what Bryant is often accused of being: a Panglossian adaptationist.
It is definitely *not* the case that an adaptationist must defend the proposition
that "every feature that exists today [has] to have some adaptive or fitness value."
Bryant mentioned the example of male nipples, which are almost comically irrelevant
to fitness.
I would say that adaptation is an extremely important effect that shapes *most*
phenotypic characteristics that do have serious fitness implications, and that when
looking for an explanation for such characteristics adaptation should at least be
considered as a likely candidate.
>
> : > Gould & Vrba placed less emphasis on natural selection and the resultant
> : > adaptations to explain the evolution of features, and instead with their
> : > concept of exaptations, placed more emphasis on historical constraints of
> : > all organisms ("evolutionary baggage") and the evolution of characters
> : > from what is already "there" rather than producing something from scratch
> : > as an adaptationist approach might.
>
> : "Producing something from scratch" is *not* an explanation that a typical
> : adaptationist would make. It *may* be an explanation that a naive adaptationist
> : would make. The role of historical constraints fits very nicely within the
> : adpatationist framework.
>
> I believe the argument there *would* be that many adaptationists would
> argue features which optimize fitness today did arise via natural
> selection and evolve through time ("historical genesis") for their
> current roles. If that is not producing from scratch, then you are saying
> adaptationists feel as Gould and Vrba do then. In which case we're
> not talking about adaptations at all, in Gould's view anyway.
I don't think Gould has the right to define the terms of the debate. As I explained
with the ear/jaw example, the notion of adaptation co-opting what's already there for
a different purpose is a very old idea, and I'll bet anything that it goes all the
way back to Darwin.
>
> : > I don't know if that helps either side of the discussion, but the concept
> : > of exaptations does eliminate the need to explain every currently
> : > "adaptive" (functionally useful) feature as having historically originated
> : > and evolved due to selection pressures for that current use. Theirs is a more
> : > narrowly delineated concept of what an adaptation is. Just because
> : > something is adaptive today, doesn't necessarily mean it evolved via
> : > natural selection for that reason. When it comes to features, it's not
> : > necessary to explain all functionally significant characters as products
> : > of natural selection in Gould & Vrba's more narrowly defined
> : > adaptationist view.
>
> : First, exaptation is far from the universal paradigm of evolution, no matter how
> : much the self-aggrandizing Gould would like it to be. Second, Bryant is not
> : claiming that "just because something is adaptive today, [it must have] evolved
> : via natural selection for that reason." He has very specifically said that he is
> : not claiming that.
>
> I never claimed that Gould's exaptations concept is universally accepted,
> but it does offer an alternative to the adaptationist views, and helps to
> explain certain features of evolution which would otherwise seem
> inexplicable. In my experience, those who criticize Gould often do so out
> of a lack of understanding of his ideas.
>
It may also be because they understand his ideas, but they just don't agree with all
of them.
> Also, it's not necessary for you to tell us what Bryant has said or
> hasn't said. I had hoped he'd do it himself. In a less critical manner, I
> would hope. And with a bit more substance.
>
Bryant is more than capable of looking out for himself. He's defended me in some
other threads, so I have to admit some feeling of loyalty. I also happen to agree
with just about everything he says.
Steve Barnard
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