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Re: Ah ha! That's where therizinosaurs came from



Tim Williams wrote that adaptive explanations and phylogenetic analyses
are two sides of the same coin.

He and I differ on this. I believe that phylogeny can be assessed without
speculating about adaptations.

Moreover, adaptation is only one of several explanations for any
particular morphological change.

Lastly, I will add that phylogenetic hypotheses can be tested, repeated by
other workers, and supported or falsified, making them highly helpful in
finding the truth. Adaptive hypotheses, on the other hand, are often
offered without any method of testing them. For example, if we say that
several lines of avialans lost teeth independently because enamel is dense
and losing it helps lighten the head and body overall for flight, then how
can we test this? How could we support or falsify this hypothesis? Even if
we had living populations of basal avialans, and we could sample them and
see that, in one subpopulation, toothlessness was becoming more prominent
and this group was probably undergoing speciation. Even then how could we
demonstrate that the reason for this was the 1 gram weight advantage that
toothlessness gave those individuals in flight?

I recommend these discussions of pleiotropy and other factors that can
produce such changes:

This one documents amazing pleiotropies and the loss of eyes in cave fish

http://findarticles.com/p/articles/mi_m1134/is_5_114/ai_n13811128/?tag=mantle_skin;content

and this one is a classic, if obnoxious, critique of adaptationism

Gould, S.J. and Lewontin, R.C. (1979) The Spandrels of San Marco and the
Panglossian Paradigm: A Critique of the Adaptationist Programme.
Proceedings of the Royal Society of London. Series B, Biological Sciences,
Vol. 205, No. 1161, The Evolution of Adaptation by Natural Selection (Sep.
21, 1979), pp. 581-598.



> Jason Brougham <jaseb@amnh.org> wrote:
>
>> Perhaps it is the very notion of adaptive explanations that I'm
>> skeptical
>> of. I have more faith in sober surveys of the distribution of characters
>> rather than coming up with speculative explanations for the apparent
>> pattern.
>
>Tim Williams wrote:

> To me, these are two sides of the same coin.  Phylogenetic analysis
> provides us with a distribution of characters.  Adaptive explanations
> can then be inferred from the given distribution of characters.  As
> one example, the transition from bipedality to quadrupedality has
> occurred several times in Dinosauria.  But the adaptive explanation
> for each individual transition may differ, depending on the clade
> concerned (sauropodomorphs, thyreophorans, ceratopsians,
> iguanodontians).  They are only "speculative" in the sense that they
> are ultimately untestable.  That doesn't make them any less rigorous,
> or any less scientific.
>
>
>> A lot of elegant adaptive explanations, ones that thousands and
>> millions of words have been written about, have been proven false by
>> later
>> evidence. The idea that dinosaurs (they didn't say non-avian then) went
>> extinct because they were cold blooded and the world got too cool for
>> them
>> is just one such doozy.
>
>
> That's science.  It doesn't really matter how many "wrong" adaptive
> explanations came before.  As more and more discoveries emerge close
> to the origin of avian flight, we can get a clearer picture of how and
> why theropods took to the air.
>
>
>
>
>
> Cheers
>
> Tim
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org