Lucy in Newsweek
SmissenR at LANDCARERESEARCH.CO.NZ
Fri Apr 2 11:21:21 CST 2004
It seems to me that a phylogenetic hypothesis, like any other, should be
modified to accommodate all the available data, not just morphology or
molecules. It is quite unscientific to simply prefer one or other as
more reliable or to haggle over methods of analysis. It is the data (be
it morphology or DNA) that a phylogenetic hypothesis should explain.
Numerous explanations are available as to why either type of data can be
highly misleading in particular sorts of situations. From even the very
little mitochondrial DNA sequence data I've actually looked at, it is
numbingly difficult to explain the similarities between humans and
chimpanzees (as compared other apes) by simple parallelism or
convergence. What other explanations are available? Lineage sorting?
Human-chimp introgression? Genetic engineering by extraterrestrial
aliens? Divine humour? Do they also explain similarities in nuclear
genomes? On the other hand, what governs the evolution of the sorts of
morphological characters linking humans to Orang-utans - are some of
them based on quantitative variation under polygenic control and thus
likely to shift quickly back and forth under moderate selection?
Personally, for my own group, I'm quite strident in rejecting
chloroplast DNA trees as representative of overall species relationships
because I can advance realistic explanations, based on the biology of
the organisms, for why they might be misleading. When it comes to ape
phylogeny, the molecularists might seem far fetched when they say
apparent synapomorphies shared by humans and orang-utans are the result
of convergence or parallelism, but so far I haven't seen ANY alternative
explanation of the apparent molecular synapomorphies of humans and
chimps seriously advanced. At least until then, I'll leave my money to a
chimp over an orang-utan. cheersRob
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