[Taxacom] Molecular phylogenetic hypotheses

[John Grehan]

As someone who is in the thick of it when it comes to morphological and
molecular (base sequence) incongruence, I found the prior discussion
interesting as it seems to point to the reality that when they do
contradict each other there is no universal recipe to choose between
them. I may personally believe that the scope and number of shared
derived morphologies for humans and orangutans as well as fossil
hominids and various other fossil apes is better evidence of their close
relationship than the molecular similarity for humans and chimpanzees.
But that does not mean that this is necessarily so.

I and my colleague in this disputation have laid out arguments as to why
the molecular evidence may produce an erroneous inference, but that does
not mean that we are necessarily correct. Neither does the molecular
doubt about morphology (which is also genetic) demonstrate the molecular
proposition. Mixing the two in a 'total evidence' approach only
obscures, rather than resolves the contradiction. In this case there was
not already doubt about the position of a species. Rather the
contradiction has raised the possibility (excluded by 99% of practicing
biologists) of doubt.

Perhaps in most cases there is no issue when the level of molecular and
morphological incongruence fails to raise any red flags. Even where it
may be that 'most of the time' morphology and DNA (base sequences)
correspond, one finds some incongruence in detail (of one or few species
for example) that is glossed over because of the majority match. 

John Grehan 

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kim van der
Linde
Sent: Tuesday, August 17, 2010 11:13 PM


My experience, most of the time, morphology and DNA correspond. Often, 
when not, there was already doubt about the position of a species. So, I

actually do not see the problem so much.

Kim