Re: DNA news stories: bird and mammal evolution

["Toby White" <mwhite@houston.rr.com>]

In principle, I suppose that DNA results are testable in the same way as
morphological results: try another run with more characters.  That would
really help here, if anything would.  The authors looked at one gene out of
(at a guess) 50,000 in the nuclear genome. That's a little like tring to
construct a morphological cladogram based only on characters of the second
phalange of the right forelimb digit 3.

BTW, I looked up another famous result in this area. Mindell et al (1997)
used mtDNA to decide that flamingos were the sister group of the hoatzin!
A couple of years later, he did a very limited, but methodologically much
better piece [Mindel et al. (1998)], then tossed the whole thing because he
didn't like the result.  <Sigh>.  I understand he's got a really nice
project going right now that should give much more reliable results.

--Toby White

The Vertebrate Notes at:
http://home.houston.rr.com/vnotes/index.html and
http://www.dinodata.net

Mindell, DP, MD Sorenson, CJ Huddleston, HC Miranda, Jr., A Knight, SJ
Sawchuk & T Yuri (1997), Phylogenetic relationships among and within select
avian orders based on mitochondrial DNA, in DP Mindell (ed.), Avian
Molecular Evolution and Systematics. Academic Press. pp. 213-247.

Mindell, DP, MD Sorenson & DE Dimcheff (1998), Multiple independent origins
of mitochondrial gene order in birds. Proc. Natl. Acad. Sci. 95:
10693-10697



----- Original Message -----
From: "Ronald Orenstein" <ornstn@home.com>
To: <mbonnan@hotmail.com>; <dinosaur@usc.edu>
Sent: Thursday, July 05, 2001 8:29 AM
Subject: Re: DNA news stories: bird and mammal evolution


> 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
> 1825 Shady Creek Court
> Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com
>
>