Re: Question: Population Bottleneck and "out of Africa"
- From: Ron O <rokimoto@xxxxxxx>
- Date: Fri, 12 Oct 2007 14:08:55 -0400 (EDT)
On Oct 8, 12:45 pm, nos...@xxxxxxxxxx (Paul Ciszek) wrote:
In article <fe8r26$1aa...@xxxxxxxxxxxxxxxxxxx>,
Ron O <rokim...@xxxxxxx> wrote:
Most of the genetic variation in the human population is still in
Africa, but even that shows that there was a bottleneck where the
effective population size of humanity was pretty small. I've seen
estimates of on the order of 1,000. Several sub populations
apparently made it out of Africa after this bottle neck and show the
expected reduction in genetic variation of taking a part of a larger
population and moving it somewhere else. The populations outside of
Africa do not show detectable mixing from populations of Homo that may
have been in the areas that they were moving into. They mainly show a
part of the variation that exists in Africa.
No, I didn't mean that after the bottleneck, people moved out of
Africa and mixed with survivors elsewhere. No, lettuce assume for
the moment that the bottleneck survivors where 1,000 people in Africa,
and everyone else on Earth died. So of course, everyone alive today
shows the out-of-Africa genetic subset pattern that you describe in
the later text that I cut. That makes perfect sense; what diversity
was left after the bottleneck spread through Africa, and subsets of
that emmigrated.
The other populations do not have to die out. The sub population just
has to expand and take over the ranges of the other extant populations
without remixing. It is called speciation.
My question was the following: Doesn't the bottleneck event destroy
genetic evidence of *previous* geographic wanderings? Could some
of the Homo Erectus that went to Asia have had descendents who
wandered back west again, and re-mixed with the Homo Erectus gene
pool in Africa *long before modern humans emerged*? Is it possible
that the 1,000 modern humans in Africa that survived the most recent
bottleneck event themselves had ancestors (if you went far enough
back) among those *earlier* populations of pre-humans that wandered
about?
Yes, but if we had extant Homo erectus we might be able to tease out
whether they made it back into Africa and contributed. We would need
genetic evidence, and since they are all dead and we can't seem to get
any DNA that old out of the fossils we have to resort to other means,
like trying to identify odd bits of the genome that may show evidence
of intermixing due to their patterns of DNA sequence variation.
Our ancestors seem to have been travelling all over the place long
before "we", i.e., anatomically modern humans, existed. When you
have a highly mobile species with a large, contiguous geographic
range, shouldn't there be mixing throughout the population?
Right now we can't rule out that there was migration back into
Africa. The horse example where the ancestors of modern horses may
have come back to Asia from North America is such an example that we
seem to have fossils to demonstrate. It used to be that the Homo
erectus skulls with the largest cranial capacity were found in Asia,
but I haven't kept up with the research in years.
Ron Okimoto
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- From: Paul Ciszek
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