Re: 'Out of Africa' still only a theory?!?!?
NeilFoglia (neilfoglia@aol.com)
30 Sep 1995 09:14:33 -0400
I have been on both sides of this issue. Originally I held to the
multiregional model and it is only within the past few months that I have
found the Out of Africa model more compelling. How anyone can support
either model is not a mystery to me, the real mystery for a laymen such as
myself, is how does anyone decide this issue firmly for themselves?
There is little doubt that the genus homo originated in Africa. If there
were two migrations out of Africa, there is some controversy over when the
first occurred. If the early dates assigned to the Java fossils are
correct, then erectus left Africa almost as soon as this species appears
in the African fossil record. Given what we know about speciation, a
plausible argument can be made that if erectus was widespread and fairly
numerous, then little in the way of speciation would have occurred. The
multiregional model with its generous amount of genetic exchange begins to
look suspect.
Conversely, if erectus populations were small and fragmented, "out of
Africa" is more in line with Mayr's concept of founder populations and
even punctuated equalibria, whereby small isolated populations give rise
to new species. Of course, neither concept argues for a strictly African
origin, but they do stress small isolated populations as a prerequisite
for speciation.
Out of Africa does contain many assumptions. One assumption is that homo
erectus and homo sapiens are different species. Having been influenced by
Tattersall's "The Fossil Trail", I am inclined to believe that Homo
erectus may be comprised of more than one species and that therefore Homo
sapiens is separate and distinct from most, if not all, Homo erectus
populations.
In "The Neandertal Enigma" Jim Shreeve points to a greater amount of
genetic diversity in African populations as indicative of an African
origin of modern humans. A question I have is whether there may be other
factors e.g. less selection, greater mutation rate, heterosis, higher
birth rates or something else, that would account for higher diversity in
African populations? Then we have to ask, how likely are these other
factors as opposed to an African origin?
The anatomical evidence for me remains unclear. It appears that a case
for either model can be made based on the fossil evidence. When I was a
"multiregionalist" Stringer's "In Search of the Neanderthals" failed to
convince me. Neither did Leakey's "Origins Reconsidered" or Johanson's
"Ancestors". Strangely, the two books that caused me to reconsider out of
Africa, were Eldgredge's "Reinventing Darwin" and Tattersall's "Fossil
Trail" even though neither book was concerned with this issue.
James Shreeve's book appears to weigh in heavily in favor of out of
Africa, but he does provide a fair balance and leaves room for doubt on
what will probably remain one of the biggest mysteries of our existence.
Of course, now that I am more receptive to the out of Africa model, I
found his arguments compelling. But I still can't say that the case is
closed.
The subject of modern human origins is one that I would like to see more
of in this newsgroup.
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