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

Susan S. Chin (susansf@netcom.com)
Sat, 31 Aug 1996 04:05:16 GMT

Bryant (mycol1@unm.edu) wrote:
: In article <lpiotrow.391.32259CD8@magnus.acs.ohio-state.edu>,
: Len Piotrowski <lpiotrow@magnus.acs.ohio-state.edu> wrote:
: >In article <502e7h$3gje@argo.unm.edu> mycol1@unm.edu (Bryant) writes:
: >
: >This is all well and good, but as I've made clear, the problem that arose was
: >with your "sugar craving" and "jealousy" traits as apparent counter examples.

: I thought that I pulled those from my hat to illustrate (crudely) how
: once-adaptive traits need not be currently adaptive. I think I was
: critiquing problems with optimality models (something Gould and I agree
: about), not attacking Gould.

: I could be mistaken, but I thought that you pulled the various quotes
: from different msgs and put them together to show that I was being
: inconsistent by saying Gould overstates his case and then daring to
: speculate about the adaptive function of sugar craving and sexual jealousy.

: >>[snip] The male nipple has no apparent likely fitness effects.
: >>It is probably a developmental side-effect of some kind. Baggage.
: >
: >Then I guess you would agree that there are other possible processes
: >accountable for the existence of these "traits."

: Of course. How many times must I say I'm not Dr. Pangloss before you'll
: believe me?!

: >These were juxtaposed in context with the Gould & Lewontin critique, not,
: >interestingly, as examples of "functional design," but as an apparent counter
: >to Gould & Lewontin's claim. I merely pointed out that they *were* examples of
: >"functional design," something to which you took some exception.

: I think I just communicated poorly. And perhaps misunderstood your point.
: I think that the adaptationist program is sensible; look for a functional
: "purpose" for a trait before dismissing it as the result of non-selective
: forces of evolution. It's easier, usually, to test the predictions
: derived from adaptationist hypotheses than from hypotheses which posit
: that a trait has no functional significance.

: Bryant

Lenny, Bryant -

I've been reading your discussion here with some interest, and I'd like to
offer my point of view on this. Instead of two POVs, we'll likely end up
with three when I'm done.

I have not read the Gould & Lewontin article referred to in this thread,
but am fairly familiar with Gould's work, and his ideas about evolution.

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." Conversely, features which today may serve no
apparent purpose or usefulness, and would therefore be expected to be
lost due to selection pressures against retaining such traits, are
somehow still around. Gould's view of exaptations nicely "solves" this
problem by stating that characters which may appear useless can serve a
function in the future, as a feature "co-opted" for a previously
non-existant need. This concept of exaptations also works well for
features which previously evolved for one purpose and now serves another,
or several uses which optimize fitness. They would consider the original
use the "adapted" feature, the new or added utilities of a feature as
"exaptations."

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.

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.

Sorry if I'm being a bit redundant in the last paragraphs. But these
concepts are not always easy to discuss, much less explain coherently.

Susan

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                                             susansf@netcom.com