Re: Constraints (was Re: Adaptationism's Lessons)
Bryant (mycol1@unm.edu)
19 Sep 1996 14:20:23 -0600
In article <51q2sg$edf@panix2.panix.com>, Paul Gallagher <pcg@panix.com> wrote:
>
>The Lenski paper shows how important random drift is in moving about the
>adaptive landscape in a real population of E. coli. Genetically identical
>populations in identical environments end up with many different morphologies.
You misunderstand me. I said that the adaptationist program seeks to
understand the evolutionary function of traits which exist, not to
predict what will come to be.
Your example (an excellent one, by the way--I'll look up the paper) shows
only that there are multiple adaptive peaks and that selection acts on
whatever raw material (genetic "fodder") is at hand. Founder effects
can, in this way, indeed be powerful for determining later results. But
there are adaptationist interpretations for each morphology, you suggest.
>How has selection predicted the design in this case? (And why don't you
>consider ideas about random drift "prediction testing science"?)
Actually, you provide a nice example of how it can be. But I was
referring to the difficulty I see with identifying traits which are due
to drift. Showing that drift (in the form of a founder effect) is
important is valuble, but explaining existing traits as results of drift
is much harder to establish. I think. I mean: How do you defend the
position, long held, that beetle horns are not the result of selection?
It's easy to think of ways to test current function, or through
comparative methods, to test likely historical functions. But drift?
How do you explain that??
>>Since I've quoted the Spandrels paper to negate an earlier mistake of
>>yours, perhaps you can take my word for my having repeatedly read through
>>it.
>
>I don't think I was mistaken. I think there's a difference between accusing
>someone of thinking "all traits are currently adaptive, and optimally so,"
>and accusing them of thinking "most traits are adaptive, and close to
>optimal."
That wasn't the quote. Gould said, as I quoted earlier, that
evolutionists are "exclusively" interested in the optimal design and
current utility of traits. Have you read the Spandrels paper?
>Anyway, I think Gould and Lewontin are making more points
>beyond a critique of optimization theory. They have written articles
>on the subject, but they dealt with other topics here. In particular,
>they advocated Seilacher's construction morphology. This is the idea that
>morphological analysis requires morer than functional analysis. Just
>elucidating the function of a trait does not explain it. You need to
>address phylogenetic, structural, ecophenotypic, and chance factors as
>well to get a complete and useful explanation. These latter four factors
>aren't just something holding back adaptation. They're equal players in
>determining the form of an organism.
Agreed. But one can assume that adaptations reflect what selection had
to work with. That's obvious. What's not always as obvious is what the
historical function of a complex trait is.
>In particular, I don't understand why you (and Dennett too)
...and Cronin... :)
>think showing a function for the divaricate patterns on shells in some
>organisms proves Gould and Lewontin wrong.
They mocked Wallace for suggesting such a thing. They said he was the
epitome of a Panglossian. You don't think that his turning out to be
correct weakens their case for a need for a major revision in the way we
do evolutionary biology?? Not even a tad?
>They themselves discuss the function of these patterns
>in some organisms. But Seilacher's idea is that that these are secondary
>adaptations. They are functional now, but their origin may not be adaptive.
Meaningless! ALL traits were originally chance changes in phenotype.
Subsequent selection history is the question.
>But I'll let you have the last word. We're too far apart in our positions
>to have a useful discussion.
Too bad. I was getting some useful perspectives from the interaction.
Must folks nod continuously for a conversation to be useful?
>Paul
Bryant
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