update on Human-orangutan origins

[John Grehan]

Just a brief update on the subject for those interested.

One of the currently proposed synapomorphies appears to be invalid. This
concerns the smoothness of the nasal floor from the nostril. Humans and
orangutans are distinct among all primates in having the smoothes
(flattest) surface. Chimps and gorillas and other primates have a "step
down" from the nostril. This stepping down is also present in
australopithecines and has (if I recall correctly) been used to support the
African ape connection, but since the step down is a plesiomorphic feature
for apes this similarity is not indicative of a close relationship. The
human and orangutan condition appears to be autapomorphic for each as the
human pattern involves a different formation of the bones between the
premaxilla and palate compared with the orangutan. So with that character
excluded the total would be down to 41. However, the 'Mona Lisa' smile
appears to be supported as a uniquely shared character for humans and
orangutans so that will be added.

There is potentially another human-orangutan synapomorphy in the structure
of female genitalia. This has yet to be corroborated in detail, but one
author has indicated that humans and juvenile orangutans share the same
basic structure compared with other primates (the juvenile condition might
make sense in the context of the generally accepted view that humans
represent retention of juvenile characteristics). If verified this would
provide an significant addition to the range of other reproductive
synapomorphies between humans and orangutans.

On the other side of the coin I will be looking further into the 'genetic'
question. I agree fully with Curtis that my own understanding of molecular
systematics needs to be improved so I can better articulate the problems or
issues as I see them (although one can see the complexities of this in view
of the different points of view that were expressed about parsimony vs
other techniques applied to molecular characters. On the other hand, I also
need to learn the definitive demonstration of various molecular claims
about veracity of DNA sequence characters, their necessary relationship to
phylogeny and morphology, and their 'cladistic' status etc. (Curtis - if
you could give me a citation for whom you view as the authority
demonstrating the cladistic nature of DNA sequences by which cladistics is
no longer to be represented by the theoretical propositions of Rosa,
Hennig, Nelson etc I would be most grateful).

John Grehan




Dr. John Grehan
Director of Science and Collections
Buffalo Museum of Science
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