[Taxacom] hominid evidence

John Grehan jgrehan at sciencebuff.org
Wed Jul 1 07:28:33 CDT 2009


Thank you for the elaboration. I will (at your suggestion) copy my
response to the list as your points may seem minor, but they concern
general questions of character analysis and interpretation.

Skin color - it's an assumption that dark color is ancestral for humans.
Perhaps it is, but I am not aware that other variation was not included
in the ancestor as well. And what is 'dark'. There are many variations
of density of melanin. Is darker more ancestral than lighter shades of
dark? Maybe others could comment on this.

Chimpanzees have a dark tone (darker than modern humans?), but they also
have very pale pigmentation. If both are present in chimps, then why not
the first hominids? Gorillas appear to be darker than most humans, but I
have seen newborn gorillas with an almost pink tone. 

Orangutans appear to have a lighter tone, but it's still a 'dark' brown
to brownish-grey that can be very dark in some individuals (this is just
my impression so I may be corrected) as well as having relatively pale
color tones. 

These uncertainties aside, the proposition that 'dark' is uniquely
shared between humans and African apes (in which case it is
uninformative about the human-chimpanzee relationship) it should not
occur in the 'ougroup'. But skin color in the lesser apes (sister group
to humans and great apes) appears to be also as dark as some African
apes). If one moves to the next sister group, the Old World monkeys, one
finds every shade under the sun so to speak. 

The outgroup comparison suggests that skin tone provides no support for
an apomorphic state shared between humans and African apes. A similar
argument would apply to hair color, with hylobatids and monkeys having
dark and light tones, and even in gorillas there are reddish-brown tones
while in orangutans the color can range from the predominant
reddish-brown to very dark (I recall reading somewhere that they can be
black, but I would have to dig into the literature to be sure).

There are many more morphological similarities shared between humans and
African apes than with orangutans, but this seemingly 'overwhelming'
evidence is comprised mostly of features that are common in gibbons and
monkeys and therefore may be considered plesiomorphic for the
large-bodied hominoids (humans and great apes).

John Grehan 

> -----Original Message-----
> From: Dr. David Campbell [mailto:amblema at bama.ua.edu]
> Sent: Tuesday, June 30, 2009 5:27 PM
> To: John Grehan
> Subject: RE: [Taxacom] hominid evidence
> > I am not aware of any uniquely shared hair and skin color traits for
> > humans and African apes. Can you elaborate?
> The plesiomorphic color for Homo sapiens is very dark, like that of
> chimps and gorillas, versus the reddish for orangs.  Not a major
> character, just the first similarity that came to mind.
> Most dubious molecular results that I have encountered have either
> support, poor techniques, or ill-behaved genes, evident with
> to other genes.  However, there are plenty of cases in which the
> molecular data don't give much of an answer.
> I'm more a paleontologist myself, but am doing a lot of molecular work
> a) as an additional line of evidence on evolution and b) in vain hopes
> it will help me get employed.
> (I'm replying to you because I'm not so sure this is of general
> interest, but you can reply to the list if you like.)
> --
> Dr. David Campbell
> 425 Scientific Collections Building
> Department of Biological Sciences
> Biodiversity and Systematics
> University of Alabama, Box 870345
> Tuscaloosa AL 35487-0345  USA

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