[Taxacom] DNA only descriptions

[Stephen Thorpe]

John Grehan wrote:

>The discrepancies between molecular and morphological phylogenies are
not 'explained' by doing both. The discrepancy may, for example, be due
to a flaw in one or both methods that is not addressed simply by doing
both. In human-great ape systematics, for example, combining molecular
and morphological evidence does not 'explain' anything. It just obscures
the fact that there is a wealth of uniquely shared morphological
similarity that does not agree with patterns of molecular similarity.

Demanding that people do both morphology and molecular comparisons
obviates the possibility that there are credible reasons for why one my
reject one or other line of evidence. I would consider it an unjustified
totalitarian and unscientific restriction.<

Oddly, I find myself in perfect agreement! Using two sets of (more or less) 
independent data is good if the results agree (it increases confidence), but 
does not help if the results disagree. It is unclear how best to handle 
conflicting sets of data, except by finding a plausible explanation why one set 
or other might be wrong ...

Stephen


 



________________________________
From: John Grehan <jgrehan at sciencebuff.org>
To: taxacom at mailman.nhm.ku.edu
Sent: Sat, 21 August, 2010 12:52:21 AM
Subject: Re: [Taxacom] DNA only descriptions

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Sergio Vargas

> yes and no... I see big problem with either morphogical folks
> focussing on morphology and molecular folks focussing on molecules, in
> my experience if do this you MAY end up simply communicating that a
> the taxonomy of a group is a big mess or that this genus is
> para/polyphyletic without any nomenclatural consequence of this
> results. The discrepancies between molecular and morphological
> phylogenies deserve to be explained and you cannot do this unless you
> do both... even if it is hard.

The discrepancies between molecular and morphological phylogenies are
not 'explained' by doing both. The discrepancy may, for example, be due
to a flaw in one or both methods that is not addressed simply by doing
both. In human-great ape systematics, for example, combining molecular
and morphological evidence does not 'explain' anything. It just obscures
the fact that there is a wealth of uniquely shared morphological
similarity that does not agree with patterns of molecular similarity.

Demanding that people do both morphology and molecular comparisons
obviates the possibility that there are credible reasons for why one my
reject one or other line of evidence. I would consider it an unjustified
totalitarian and unscientific restriction.


>By criticizing every molecular-only study, you are demanding
> that every molecular researcher essentially carry out two high-quality
> studies.
> Are you prepared to demand the same from every morphologist?

> I am, and most highly cited journals are too. Curiously, you can
> publish a molecular only study without any further discussion on the
> discrepancy with morphological expectations (but the classical
> taxonomy is a mess) in many highly cited journals but you cannot do
> the same using morphology only. You would need "independent sources of
> evidence" to assess the validity of the phylogeny. I now work with
> molecules but try to include morphology and nomenclatural issues in my
> work when ever possible.

Acknowledgement and discussion of discrepancies is fine. But as for
molecular similarity (of the current kind) representing an 'independent'
evidence to assess the validity of the phylogeny is just stupid (in my
opinion), particularly where fossils are involved.

> here you come to an important point. I think there should be more
> communication between morphologists and molecular systematists, and
> less interest in proving oneself right at all cost

I could not agree more, but in the human origins field the exact
opposite occurred, where molecular supporters ignored the morphological
contradiction for quarter of a century, and only recently indicated some
pain when the orangutan phylogeny paper got too much attention.

John Grehan



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