[Taxacom] Why character-tracking doesn't happen?

Neil Bell neil.bell at helsinki.fi
Fri Sep 12 10:34:49 CDT 2008


Thomas G. Lammers wrote:
> The main problem of course is that cladistic methodology is such a poor 
> reflection of how evolution operates in nature.  It assumes that the 
> entities evolving are discrete units rather than aggregations of 
> individuals and populations; it assumes evolution is always dichotomous and 
> that reticulation never occurs.  Add on to that unsubstantiated a priori 
> assumptions like "paraphyly is bad" and "sister taxa have equal rank" and 
> it becomes a real house of cards.
>
> Study what a population geneticist says about evolution, then study what a 
> cladist says about evolution, and you'll be hard pressed to accept they are 
> describing the same phenomenon.
>
> News flash: The emperor has no clothes!

Like any methodology it makes assumptions appropriate to the questions 
it is trying to answer. Aggregations of individuals and populations 
(generally and eventually, if by no means always) become discrete units 
through the process of speciation. Incomplete lineage sorting and 
reticulation occur and should be identified, but they are not the 
dominant patterns in the relationships between phylogenetically distant 
eukaryotic organisms. Population genetics can say no more about the 
relationship between a frog and a sparrow than cladistics can about the 
relationship between individuals within a population (probably a lot 
less actually). The reason these different disciplines appear not to be 
describing the same phenomenon is that one describes the process of 
evolution in action (or something nearer to it) while the other 
reconstructs its historical consequences.

I always find it odd when people criticise cladistics and/or 
phylogenetics without suggesting how the questions they ask could be 
better answered. The implication seems to be that either 1) the 
questions are unanswerable 2) they are not interesting, or 3) there must 
be better ways to address them but we don't know what they are...

P.S. I know few phylogeneticists with an organismal background who 
aren't intensely interested in homoplastic morphological characters on a 
robustly supported phylogeny, i.e. credible hypotheses of convergence 
and reversal.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Neil E. Bell
Postdoctoral Researcher
(Bryophyte Systematics)
 
Kasvimuseo
PO Box 7
00014 University of Helsinki
FINLAND
 
+358 9 191 24463
neil.bell at helsinki.fi
~~~~~~~~~~~~~~~~~~~~~~~~~~~~





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