DNA and phylogeny question

John Grehan jgrehan at SCIENCEBUFF.ORG
Wed Oct 6 09:34:21 CDT 2004

In my continued look at the relationship between DNA base sequence
similarities and phylogeny (the orangutan problem) I am still coming to
what seems to be a dead end in my efforts to determine what evidence
there is, if any, to show that DNA base sequence similarities
necessarily 'prove' phylogeny to the exclusion of any conflicting
morphological evidence (the classic chimpanzee example). To date the
evidence seems to be limited to a sort of rhetorical position such as
morphology is subject to selection and therefore more misleading (I
presume this is in comparison to non-coding DNA only), or that patterns
of DNA similarity from different 'genes' is internally consistent (and
statistically significant) and therefore is a necessary proof of greater
reliability - particularly when put through a 'cladistic' program
(although again that seems to be an inference rather than a
demonstration). I recently met a hominid specialist who asserted DNA was
the final proof of hominid relationships and the person was quite
affronted when I asked for why that was necessarily so. However, no
evidence of that position was forthcoming.


I recall some years back that there were comparisons of predicted
phylogeny and actual patterns of descent for populations of bacteria in
cultures which certainly demonstrates that DNA sequence can predict
phylogeny (at least on this scale) but again it does not say whether it
necessarily does so under all circumstances ( as a sort of analogy to
the congruence of phylogenic and island emergence sequences in Hawaii
showing that congruence between phylogeny and geology can reflect
dispersal while not demonstrating that this is the only mechanism for
such congruence). There are also the genetic arguments that, in
"general", DNA sequences similarities correspond to morphologically
based phylogenies. Again this might show that DNA sequence similarities
can match phylogeny, but then it is not a demonstration that it
necessarily does so when in conflict with morphology.


If anyone could add anything to the above I would be pleased to hear. I
am really trying to discern whether the authority granted to DNA
sequence similarities has some tangible support or is really more of a
belief system imposed upon the data (like dispersalism). I gather from
earlier reactions on the list that some are fed up with my line of
inquiry so perhaps respondents could email me directly so as not to
further upset those subscribers.


John Grehan



John R. Grehan
Director of Science and Collections

Buffalo Museum of Science

1020 Humboldt Parkway

Buffalo, NY 14211-1193

email: jgrehan at sciencebuff.org

Phone: (716) 896-5200 ext 372






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