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

[Stephen Thorpe]

Hi Ken,
Yeah, I know John could very well be described as something of an  
"extremist", but I was just trying to make the point that there is  
usually at least a grain of truth on both sides of most disputes. I  
note that you have dropped the "propaganda" issue. The relevance of  
the scyd example, and indeed Xenoturbella, is that going back and  
error checking can be difficult or impossible with huge datasets for  
cladistic or molecular studies. The source of error, assuming there  
was one, for the scyds, remains unknown. Luckily, a fairly basic error  
was discovered for Xenoturbella, and it is easy enough to guard  
against in future, but who can say how many other possible sources of  
error there might be, and how easy or otherwise thay are to guard  
against? This is perhaps a problem that results from "taking the  
thinking out" of the methodology, and relying on number crunching  
machines to spit out the correct answer. Coding errors are probably  
made quite often in phylogenetic analyses, and I'm not sure how much  
"mess" even a small number of coding errors could make to a big  
dataset? I can think of a particular example where a 2-segmented  
antennal club was to be coded with a 1, but of course the author soon  
started miscoding it as a 2!
Cheers,
Stephen

Quoting Kenneth Kinman <kennethkinman at webtv.net>:

> Hi Stephen,
>       I am quite aware of the Xenoturbella contamination problem.  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).
>        However, this does not excuse using such sloppy science as an
> argument against the kind of consistent molecular evidence that Grehan
> continues to rail against.  That my acceptance  (among that of other
> researchers) of molecular methods might be too UNCRITICAL is not a major
> problem in my opinion, and rather it is Grehan's uncritical acceptance
> of morphology alone that is leading him to problems.  As for
> Scydmaenidae, I have no knowledge or specific interest in that
> particular case, but its relevance is probably not as relevant as one
> might think.  If the evidence there is equivocal, that is one thing, but
> comparing it to the orangutan case is probably a stretch at best.
>           ------------Ken Kinman
> ----------------------------------------------------------
>
> Stephen Thorpe:
>      I think there is something in what John says - specifically there
> is  "propaganda" associated with molecular methods, but realistically it
> is the UNCRITICAL acceptance of the molecular over morphological that
> leads to problems. The Scydmaenidae example is relevant here. To argue
> for "total evidence" sounds all well and
> good, but what if half of it  points one way, and half of it the other?
> Sometimes it seems like  every new method gives a different result!
> Another good example  involves the enigmatic Xenoturbella. Are people
> familiar with the  story? An uncritical molecular analysis revealed that
> it was a bivalve  mollusc without a shell! Then it was discovered:
> Bourlat, S.J.; Nielsen, C.; Lockyer, A.E.; Littlewood, D.T.J.;  Telford,
> M.J. 2003: Xenoturbella is a deuterostome that eats molluscs.  Nature,
> 424: 925-928.
>
>
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