[Taxacom] hominid challenge and Pavetta challenge

[John Grehan]

Stephen's comments below show that he understands (not to imply
necessary agreement) my argument exactly and the implied challenge for
the systematic integration of fossil and living taxa where there is
molecular incongruence.

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Stephen Thorpe
 
> OK, if the argument is this (see below), then it is stronger:
> Molecular evidence applied to extant hominids shows that the
morphological
> characters that we have to rely on (for lack of any alternatives) in
the
> case of fossil hominids are completely unreliable indicators of
> relationships. But does it really show that?

Yes, a molecular supporter would have to say (in my opinion) that the
morphological characters we have for fossil hominids are unreliable
because they link those hominids along with humans and orangutans, not
human and chimpanzees.

> Presumably, the case would be similar for molluscs, because
conchological
> characters alone are not good for extant molluscs, but it is all we
have
> in the case of fossils. So, how do fossil mollusc taxonomists manage?

> 
> Presumably, if you accept that molecular evidence is a priori
definitive
> of relationships (BIG assumption), then you need to try to find
> morphological characters that are congruent with the molecular results
(in
> the case of extant taxa, and then apply the morphological results to
> fossils). 

This is indeed what several morphological systematists tried to do. In
the most extensive studies they had a hard time finding any, and of
those that were claimed none appear to withstand scrutiny. Even if they
were all accepted, they are so few as to be far outnumbered by the
human-orangutan apomorphies.

> If none can be found, then there is presumably little or no
> point in trying to classify fossils phylogenetically ...

Yes! That is the challenge 

John Grehan

> 
> Stephen
> 
> ________________________________________
> From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Barry Roth
[barry_roth at yahoo.com]
> Sent: Thursday, 24 September 2009 12:08 p.m.
> To: Taxacom
> Subject: Re: [Taxacom] hominid challenge and Pavetta challenge
> 
> Yes, and the further question is, how do we decide in what cases
> morphology is (or, more specifically, what characters are) reliable?
> 
> I have enjoyed, for instance, comparing the results of molecular and
> morphological analyses of some groups of snails.  Some morphic
characters
> long relied on by systematists were incongruent with the results based
on
> DNA sequences.  Hmm, that was good to know, perhaps those are
"shallow"
> morphic characters.  Others, that many of us had long written off
turned
> out to sort rather congruently.  Ahh, worthy of a closer look; maybe
we
> didn't parse those character-states well enough.  I consider this
process
> of cut-and-fit to be sound, pragmatic systematics.
> 
> But should we accept one data set (e.g., molecules) as always
> determinative in this process?   Similarly, should geography tilt the
> balance between two otherwise equally weighty interpretations of
> relationship based on morphology?  To do so algorithmically in either
> situation is to take a fairly hard stance, it seems to me.
> 
> Barry Roth
> 
> --- On Wed, 9/23/09, Stephen Thorpe <s.thorpe at auckland.ac.nz> wrote:
> 
> 
> > if we accept, on the basis of molecular results, that morphological
> evidence is unreliable
> NOT ENTIRELY UNRELIABLE IN EVERY CASE! Morpho- evidence is likely
> reasonably reliable in most cases. A few cases where morpho- evidence
> (allegedly) gives the wrong answer doesn't mean it is totally
unreliable
> in every case ...
> ________________________________________
> From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Barry Roth
[barry_roth at yahoo.com]
> Sent: Thursday, 24 September 2009 11:30 a.m.
> To: Taxacom
> Subject: Re: [Taxacom] hominid challenge and Pavetta challenge
> 
> It's not up to me to answer on behalf of John, but I take his question
as
> a serious methodological one:  if we accept, on the basis of molecular
> results, that morphological evidence is unreliable, how can we turn
around
> and, in a case where molecular data are unavailable, accept the
available
> morphological evidence as trustworthy?
> 
> I suppose this could be justified as "you work with what you've got,"
and
> that is of course a familiar situation for paleontologists.  But if a
> whole modality of data is dismissed as unreliable, then you shouldn't
be
> able to cherry-pick the situations where you accept and trust it.  At
> least not if consistency -- rather than special pleading -- is
considered
> a virtue in phylogenetic analysis.
> 
> Barry Roth
> 
> --- On Wed, 9/23/09, Stephen Thorpe <s.thorpe at auckland.ac.nz> wrote:
> 
> 
> 
> _______________________________________________
> 
> Taxacom Mailing List
> Taxacom at mailman.nhm.ku.edu
> http://mailman.nhm.ku.edu/mailman/listinfo/taxacom
> 
> The Taxacom archive going back to 1992 may be searched with either of
> these methods:
> 
> (1) http://taxacom.markmail.org
> 
> Or (2) a Google search specified as:
> site:mailman.nhm.ku.edu/pipermail/taxacom  your search terms here
> _______________________________________________
> 
> Taxacom Mailing List
> Taxacom at mailman.nhm.ku.edu
> http://mailman.nhm.ku.edu/mailman/listinfo/taxacom
> 
> The Taxacom archive going back to 1992 may be searched with either of
> these methods:
> 
> (1) http://taxacom.markmail.org
> 
> Or (2) a Google search specified as:
> site:mailman.nhm.ku.edu/pipermail/taxacom  your search terms here