Re: Evolution, "adaptation", and what's currently adaptive

Susan S. Chin (susansf@netcom.com)
Sat, 31 Aug 1996 17:23:23 GMT

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. 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?

: 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?

: > 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 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.

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.

Susan

-- 

                                             susansf@netcom.com