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Tantalising clues have been emerging for some time from human
genomes that Neanderthals may have contributed a few genes to
posterity after all. That `we' mated with `them' occasionally.
The clues come in the form of widely differing DNA sequences
that seem to converge on common ancestors that lived long before
modern human beings came out of Africa 80,000 years ago or so.
There is good reason to be cautious -- it is possible that it
just means lots of very distantly Africans joined the migration --
but now it seems a tipping point is being reached in the debate.
The latest study of 600 microsatellite (fingerprint) sequences from
2,000 people is being interpreted as evidence of two separate
episodes of genetic mixing between Neanderthals (or
heidelbergensis) and ex-African `moderns'. SeeNeanderthals may have interbred with
John Hawks, who has good instincts in these matters, reckons the
conclusion is probably right:
I take it as very likely that the strict
out-of-Africa replacement without interbreeding is no longer
credible. We've moved beyond it, and all these papers are
testaments to that.
We will soon know much better when Svante Paabo publishes the
Neanderthal genome, having extracted fragmented DNA from bones
found in a Croatia and Spain.
The Implications of this are big, but it's important not to
mislead. It means there were a few mixed-race people in Eurasia by
40,000 years ago and some of them had babies. But they were
probably few. Few or none of those babies' descendants ended
up back in Africa. It means that some of the confusing skulls and
bones from the `frontier' of African advance into Eurasia might be
mixed-race. It means that there's a tiny bit of Neanderthal in some
of us, but not all.
By the way, it's never been clear that Neanderthals were stupid.
Their brains were often bigger than ours. But they did lack a
fast-changing tool kit, and they also lacked trade -- their
artefacts never travelled far. Those two things go together. Trade
creates a collective intelligence that far surpasses what
individual brains can muster.