Rethinking 'Out of Africa' - by Christopher Stringer

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May 7, 2013

Rethinking "Out of Africa"

Christopher Stringer [11.12.11]

Topic: LIFE Intro
By John Brockman

I'm thinking a lot about species concepts as applied to
humans, about the "Out of Africa" model, and also looking
back into Africa itself. I think the idea that modern
humans originated in Africa is still a sound concept.
Behaviorally and physically, we began our story there,
but I've come around to thinking that it wasn't a simple
origin. Twenty years ago, I would have argued that our
species evolved in one place, maybe in East Africa or
South Africa. There was a period of time in just one
place where a small population of humans became modern,
physically and behaviourally. Isolated and perhaps
stressed by climate change, this drove a rapid and
punctuational origin for our species. Now I don’t think
it was that simple, either within or outside of Africa.

Christopher Stringer is one of the world's foremost
paleoanthropologists. He is a founder and most powerful
advocate of the leading theory concerning our evolution:
Recent African Origin or "Out of Africa". He has worked
at The Natural History Museum, London since 1973, is a
Fellow of the Royal Society, and currently leads the
large and successful Ancient Human Occupation of Britain
project (AHOB), His most recent book is The Origin of Our
Species (titled Lone Survivors in the US).

Christopher Stringer's Edge Bio Page

Rethinking "Out of Africa"

[CHRISTOPHER STRINGER:] At the moment, I'm looking again
at the whole question of a recent African origin for
modern humans—the leading idea over the last 20 years.
This argues that we had a recent African origin, that we
came out of Africa, and that we replaced all of the other
human forms that were outside of Africa. But we're having
to re-evaluate that now because genetic data suggest that
the modern humans who came out of Africa about 60,000
years ago probably interbred with Neanderthals, first of
all, and then some of them later on interbred with
another group of people called the Denisovans, over in
south eastern Asia.

If this is so, then we are not purely of recent African
origin. We're mostly of recent African origin, but there
was contact with these other so-called species. We're
having to re-evaluate the Out-of-Africa theory, and we're
having to re-evaluate the species concepts we apply,
because in one view of thinking, species should be self-
contained units. They don't interbreed with other
species. However, for me, the whole idea of Neanderthals
as a different species is really a recognition of their
separate evolutionary history—the fact that we can show
that they evolved through time in a particular direction,
distinct from modern humans, and they separated maybe
400,000 years ago from our lineage. And morphologically
we can distinguish a relatively complete Neanderthal
fossil from any recent human.

You could argue that they're an extreme variant of Homo
sapiens, but a very different 'race' from anyone alive
today, or, as I prefer to argue, they're a separate
species, with a separate evolutionary history. But I've
never actually said that that meant they were completely
reproductively isolated from us. We know that many
closely related species in primates, for example, can
interbreed. Various species of monkey can interbreed and
have fertile offspring, and so can our closest living
relatives, Bonobos and common chimpanzees.

In my view the Neanderthals were closely related and
probably potentially able to interbreed with modern
humans, but until recently I considered that while there
could have been interbreeding forty or fifty thousand
years ago, it was on such a small scale that all trace of
it vanished in the intervening years. But it now seems
from Neanderthal genome studies that that was not so. We
do have a bit of Neanderthal in us, you and I—it's a
small amount, but certainly not negligible..

Does that mean Neanderthals are a different species or
does it mean we should include them in Homo sapiens?
Well, they are still only a small part of our makeup now,
reflecting something like a 2.5% input of their DNA.
Physically, however, they went extinct about 30,000 years
ago. They had distinct behavior and they evolved under
different conditions from us, so I still think it's
useful to keep them as a separate species, even if we
remember that that doesn't necessarily preclude
interbreeding.

Then there are these enigmatic people called the
Denisovans, who we only know about because of DNA work
that's gone on in the site of Denisova Cave in Siberia.
The site has been known for a long time. There were some
very fragmentary human fossils from there, a finger bone;
a couple of teeth, a foot bone, and each of them have
yielded significant DNA. The surprise was that while the
foot bone DNA turned out to be Neanderthal, at the
eastern limit of their known range, the other fossils had
DNA that was quite distinct: it wasn't clearly
Neanderthal, it wasn't modern human. It was something
different.

Continues at:

http://bharatkalyan97.blogspot.com/2013/05/rethinking-out-of-africa-christopher.html

Jai Maharaj, Jyotishi
Om Shanti

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