[Taxacom] ad hoc manipulation
Richard.Zander at mobot.org
Wed Sep 5 16:26:03 CDT 2007
Given that the true answer is probably "no one will ever know" I expect this problem to turn up again and again. I think John Grehan has been saying that the number of shared traits among man and orang is most parsimoniously explained by direct ancestry. Well, that's a good hypothesis.
Ken Kinman replied that one needs some molecular support to even consider the morphological data as compelling. Well, I don't know. There is no reason the molecular data must track evolution of expressed traits. First, the data are statistically very different. Molecular data are like flips of a coin that indicate, en mass, whether a coin is (phylogenetically) loaded. Morphological data are measurements of the coin to see if it is loaded. Particular combinations of morphological data are what the molecular data are supposed to be tracking.
Molecular data on (man chimp) gorilla have been summarized by Satta et al., and many loci support either (chimp gorilla) man or (man gorilla) chimp. Has anyone checked how many loci support variants on where orang fits into a tree? Could be some different gene histories there confounding things. On the whole, it seems to me that molecular data significantly support ((man chimp) gorilla) orang, but I've not seen a summary of all the data, just some few studies.
I've also pointed out in the past that a few genes coding for man/orang morphological traits may have been silenced, then unsilenced, which would explain why molecular and morphological results conflict.
Also, note that the idea of monophyly has strait-jacketted evolutionary thinking in that a surviving ancestor similar to man-orang (expressed traits stabilized by selection) may well have thrown up an orang, then a gorilla, then a chimp, then anagenetically ended up man. The ancestor is a paraphyletic man-orang, and only two of the three surviving daughter taxa are, through selection, different. Molecular traits continue to change in the tree, but not the morphological traits.
Thus, we have two possible ways that plain old dichotomous morphology (expressed traits) trees may well differ from molecular phylogenies. Demonstrating details of expressed trait evolution (the important kind) may take fossils, or some new method, or may never be capable of the kind of resolution apparently achievable in molecular analysis of gene trees.
From: taxacom-bounces at mailman.nhm.ku.edu on behalf of John Grehan
Sent: Wed 9/5/2007 7:39 AM
Subject: [Taxacom] ad hoc manipulation
I was interested to recently read that mtDNA analysis in 1997 had put
monotremes with marsupials, but because that was such an abbearation
some other molecular systematists decided to try nuclear IGF2R sequences
and got placentals and marsupials to the exclusion of monotremes so
everyone was happy. I am interested to know of any similar examples as
it shows how morphology, when so contradictory to molecular results, can
and does result in re-analysis of molecular evidence to get the "right"
answer. This is pertinent to my interests since the human-chimpanzee
relationship is very strongly contradicted by morphology, but no one (to
all intents and purposes) is willing to accept the possibility that the
molecular evidence is wrong in this case.
For over three months I have had an article in review that has a
cladistic analysis of the morphological evidence showing that the
orangutan-human relationship is the best supported model. The editor was
not at all happy to see the molecular evidence being challenged and said
he would ensure a fair review.
Dr. John R. Grehan
Director of Science and Collections
Buffalo Museum of Science1020 Humboldt Parkway
Buffalo, NY 14211-1193
email: jgrehan at sciencebuff.org
Phone: (716) 896-5200 ext 372
Ghost moth research
Human evolution and the great apes
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