Re: Question: Population Bottleneck and "out of Africa"

"Paul Ciszek" <nospam@xxxxxxxxxx> wrote in message news:fedqb2$m45$1@xxxxxxxxxxxxxxxxxxxxxx

lettuce assume for
the moment that the bottleneck survivors where 1,000 people in Africa,
and everyone else on Earth died.

That is not a reasonable assumption -- as
you have stated it. Better (scientifically if
not morally, nor politically correctly) is the
assumption that the ~1,000 started as one
small tribe, and in the process of a great
expansion, wiped out all the rest of the
species. Perhaps it did this with superior
technology but, thinking about it now,
disease was probably a major 'weapon', as
it has been for Europeans in their roughly
similar expansion over the past 500 years.
This 'tribe' of ~1,000 had maybe domesticated
pigs, acquired diseases from them, become
immune to them, and then spread.

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.

My question was the following: Doesn't the bottleneck event destroy
genetic evidence of *previous* geographic wanderings?

It does, but I think I recall reading of
genetic evidence for earlier bottlenecks.

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?

Of course they did. Where else do you
think they came from? You have not
expressed your question clearly here --
or I can't see what you mean.

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?

The taxon has the capacity to be mobile,
but it also dislikes strangers. The first
occupants of a region will not allow
others to enter.

IMO both modern and ancient evidence
shows that there was little mixing. Eastern
and Western Neanderthals are extremely
divergent. There is the extraordinarily
wide range of fossil species in Africa, and
evidence of overlapping existence of
different species (or sub-species) --
showing that mixing was not occurring.

------------------- From a recent finding -------------------
http://news.bbc.co.uk/2/hi/science/nature/6937476.stm

Now, habilis and erectus are now thought to be sister species
that overlapped in time.

The new fossil evidence reveals an overlap of about 500,000 years
during which Homo habilis and Homo erectus must have co-existed
in the Turkana basin area, the region of East Africa where the fossils
were unearthed.

"Their co-existence makes it unlikely that Homo erectus evolved
from Homo habilis," said co-author Professor Meave Leakey,
palaeontologist and co-director of the Koobi Fora Research Project.
. . . . . "
------------------- End of recent finding -------------------


Paul.




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