Re: Fw: Most popular/common dinosaur misconceptions

["T. Michael Keesey" <keesey@gmail.com>]

On 8/19/06, don ohmes <d_ohmes@yahoo.com> wrote:
> >Because otherwise, any pair of
> >organisms will have had some unique last population representing their
> >most recent common ancestor, whether Meg. and Ig., you and fruitflies, or
> >me and E. coli.
>
> Yes. However, I feel that the boundary line of reproductive isolation, excepting unlikely cases of geographical isolation of a single breeding pair, is not bridged by one female (at least in higher animals). In other words, I believe that the "unique last population" of Iggy and Meggy, could it be analyzed, would likely be larger than one breeding pair.

You are likely (or at least potentially) correct. I presented on a
solution to this at the ISPN meeting earlier this summer: allow
"cladogenetic sets" to be clade ancestors, where a "cladogenetic set"
is a set of one or more organisms where 1) no member of the set is
ancestral to any other member of the set, and 2) every member of the
set shares at least one common descendant with every other member of
the set.

Singleton sets satisfy these conditions, since no organism is
ancestral to itself (condition 1) and condition 2 is vacuously true,
since there are no other members of the set. Breeding pairs also
satisfy these conditions (assuming it is not a case of parent-child
incest), as do some more extensive sets.

But this sort of thing doesn't affect practice much, since our level
of resolution is generally not good enough to identify members of
"cladogenetic sets". In practice, it's much the same as identifying a
population or species as the ancestor. Still I think it's a more sound
theoretical basis.

Contact me offlist if you are interested in discussing this idea further.
--
T. Michael Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com