Re: DISCOVER/Neanderthal/Homo Sap.

HARRY R. ERWIN (herwin@osf1.gmu.edu)
20 Sep 1995 13:40:04 GMT

Bearcat (bcat@netcom.com) wrote:
: Harry Erwin (herwin@gmu.edu) wrote:

: [was early H.s.s. darkskinned]
: : Very likely they were. See the published material on the Nariokotome
: : skeleton. If the Turkana Boy seems to show similar skeletal adaptations to
: : the East African savannah to those seen in modern peoples of the same
: : area, his skin color is likely to have been also very similar. That's why
: : the tropical skeletal proportions of Cro Magnon man also seems to be
: : saying something about skin pigment. Skin color is very sensitive to the
: : amount of sunlight. It appears to go from very light to quite dark in no
: : more than 3000-4000 years, given the evidence from India.

: Thanks.

: Is the reverse true as well? Do we go from dark to light in a similar
: time-frame, and if so, why?

The evidence is not so clear. With India, we have Indo-Europeans entering
from Central Asia between 3 and 4 thousand years ago, so we can do a
crude calibration that way. For Northern and Western Europe, if Renfrew
is correct, we have farmers entering from Anatolia at about the same time
and swamping the local gene pool, but that theory is a bit at varience
with the evidence. There may be estimates that can be developed on
depigmentation versus time in the area for other populations, but this is
not my field, so I will defer to the experts.

Why is the melanin lost? There are at least three possible scenarios:
1. Melanin production is deleterious in cloudy areas since it reduces
Vitamin D production,
2. Loss of genes for a dark skin is a neutral mutation in cloudy areas,
since skin cancer is less of a risk, and
3. Melanin production is maintained in tropical areas because the
deleterious effects (whatever they are--oncogenesis?) are
counterbalanced by reduced skin cancer.

Since a gradient in melanism is seen in Europe (freckling, BTW, is a
melanistic trait maintained by populations in the south and transmitted
by gene flow associated with sea trade), I suspect it is very sensitive
to the exposure to sunlight, and relaxes to an equilibrium for a given
area in less than 4000 years.

--

Harry Erwin

Internet: herwin@gmu.edu 

Home Page: http://osf1.gmu.edu/~herwin (try a couple of times)

PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"