Re: DNA news stories: bird and mammal evolution

[Ronald Orenstein <ornstn@home.com>]

At 12:40 PM 05/07/01 +0000, Matthew Bonnan wrote:
> DNA-DNA hybridization distances are not the same thing.  We have no idea
> whether the similarities we see are convergent (homoplasy, parallel
> evolution) or homologous (suggesting the inhertied sequences were
> inherited from a common ancestor).  The evaluation of morphological
> character data is not simply a matter of comparing overall similarity --
> we are looking for shared dervied or unique structures that separate
> certain taxa from others.

One question I have about DNA-DNA studies is: are they testable?  In a
cladistic study of morphological characters, you can at least go back and
see if you coded the characters properly.  In other words, what do you do
if you get a DNA result that is, on the face of it, counter-intuitive (like
linking grebes and flamingos) and may not coincide with morphological
features?  There seems to be some tendency to assume in such a case that
the DNA results are "right", but how can you be sure?

 For example, a recent DNA study on turtle origins put turtles near
archosaurs, but also put Sphenodon closer to archosaurs than lepidosaurs -
a result that flies in the face of the morphological evidence.  How do you
assess such a result?


--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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