[Taxacom] Propaganda (was: Molecules vs. Morphology)

[John Grehan]

 Unfortunately, working 'for' molecules and morphology is not so
straightforward. Of course morphological inheritance has a molecular
counterpart, but this does not automatically mean that current methods
of counting base similarities is necessarily the best way of capturing
this or any other phylogenetic signal, or better than morphological
evidence. The law of large numbers is invoked, but its just a
theoretical or philosophical principle, and one that was used in the
past by morphologists who tried to argue that the more similarities
included the better the result.

The present conundrum facing systematists is how to decide between
conflicting base counting similarities and morphological similarities.
If the former is accepted as falsifying the latter then we have a real
problem in hominid evolution where the fossil record shows morphological
relationships that are congruent with morphological relationships among
living taxa. This would have to be dismissed as phylogenetically
meaningless if the molecular theory of relationship among living taxa is
accepted - and this is what is happening at present, even though the
molecular evidence cannot inform the relationships between fossil taxa,
or between fossils and living taxa.

John Grehan

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Gurcharan Singh
Sent: Monday, August 17, 2009 12:24 PM
To: Dr. David Campbell; taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Propaganda (was: Molecules vs. Morphology)

I don't understand why we debate it as Molecules vs morphology and not
molecules and morphology. We use plants in our daily life for a variety
of purpose and recognise them on the basis of morphology. The
reliability of most morphological features depends on their
incorporation into genetic material at molecular level. Such molecular
changes are more relevant than those which don't lead to any observable
change. The purpose of Systematics is to develop means of identifying,
naming and classifying organisms preferably in phylogenetic sequence.
Molecular data definitely has great potential in decifering phylogeny,
but this goes along with morphological data.
    Let us not fight over molecules vs morphology, rather work for
molecules and morphology.

Gurcharan Singh
University of Delhi
India
----- Original Message -----
From: "Dr. David Campbell" <amblema at bama.ua.edu>
To: <taxacom at mailman.nhm.ku.edu>
Sent: Monday, August 17, 2009 9:28 PM
Subject: Re: [Taxacom] Propaganda (was: Molecules vs. Morphology)


>> It clearly demonstrates that a sloppy extraction can lead to totally
>> inaccurate results (make sure you aren't extracting genetic material
>> from the stomach or intestines).
>
> It's not just "sloppy" extractions; sometimes the organism (or sample,
> e.g. "it's already dead, so might as well try for DNA" with endangered
> species) makes it difficult for you, and there are also plenty of
> potential intermediate steps between tissue clip and extraction that
> can potentially cause trouble.  Possible contamination by bacteria is
> especially difficult to prevent, since they're pretty much everywhere
> that there are other organisms, plus places unsuitable for anything
> else.
>
> In general, more critical examination of molecular results would be
> advisable.  Not only are there the anomalies due to contamination,
> misidentification, etc., but also just because your latest analysis
> supports a clade does not mean that it is well-supported and the
> definitive final answer.  On the other hand, when a molecular clade is
> unexpected but well-supported, preferably using more than one
> analytical technique, it'd definitely worth going back and looking to
> see if there are morphological, geographical, or other correlates.
>
> -- 
> Dr. David Campbell
> 425 Scientific Collections Building
> Department of Biological Sciences
> Biodiversity and Systematics
> University of Alabama, Box 870345
> Tuscaloosa AL 35487-0345  USA
>
>
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