

Early humans may have bred with other species – twice - fun2have
http://www.newscientist.com/blogs/shortsharpscience/2010/04/early-humans-may-have-bred-wit.html

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Both of these events happened outside of Africa. Are they saying that the
descendants of these interbreedings propagated back into Africa afterward? Or
are they saying not everyone has this in their DNA?

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bh42
From:
[http://www.nature.com/news/2010/100420/full/news.2010.194.ht...](http://www.nature.com/news/2010/100420/full/news.2010.194.html)

 _...the interbreeding happened about 60,000 years ago in the eastern
Mediterranean and, more recently, about 45,000 years ago in eastern Asia.
Those two events happened after the first H. sapiens had migrated out of
Africa, says Long. His group didn't find evidence of interbreeding in the
genomes of the modern African people included in the study._

I find this very surprising. We know that there was a genetic bottle neck when
we left Africa. This is why today people from two different African ethnic
groups can be MORE different then any two people from ANYWHERE in the rest of
the world. An Inuit and an South American Indian are genetically more similar
then a Touareg and a Lemba.

How could a separate species like the Neanderthals, who spent 200 _thousand_
years in isolation in ice age Europe, contribute so little genetic diversity?

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btilly
_How could a separate species like the Neanderthals, who spent 200 thousand
years in isolation in ice age Europe, contribute so little genetic diversity?_

A single successful interbreeding incident would contribute some odd genes to
the local gene pool, but wouldn't contribute much genetic diversity once it
spread out through the local gene pool. Remember that the data suggests
exactly 2 individuals dropped into human populations that were locally in the
tens of thousands, and globally in the multiple hundreds of thousands. It
would contribute some odd genes to the pool of genetic diversity, but wouldn't
move the bar very much.

For those who think that species barriers are some sort of absolute barrier to
what is hypothesized here, it is worth considering the case of donkeys, horses
and mules. Donkeys and horses are estimated to have diverged a couple of
million years ago, but routinely can breed. The result are mules, of which
over time we've bred tens of millions.. Mules are almost invariably infertile.
However according to <http://en.wikipedia.org/wiki/Mule#Fertility> there have
been more than 60 documented cases of female mules successfully bred by
stallions. The foals would be mostly horse, and the result of that is an
animal that is 3/4 horse which therefore is likely to be able to breed with
other horses.

It is not unreasonably by comparison that there could be a constant level of
interbreeding between us and Neanderthals, with many infertile offspring, and
by chance on 2 occasions fertile offspring who have descendants today. (The
overall number of crossbreeds would be lower than the number of mules, but
their odds of fertility would be much higher than for mules.)

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netcan
This would also suggest a reasonable chance that some hybrids bred back into
the Neanderthal populations instead of ours.

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btilly
Odds are high that those hybrids are now evolutionarily irrelevant.

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bh42
More details here:
[http://www.nature.com/news/2010/100420/full/news.2010.194.ht...](http://www.nature.com/news/2010/100420/full/news.2010.194.html)

 _The ancient mitochondrial DNA came from a piece of finger bone, which the
groups haven't identified by species. It could be Neanderthal, a new Homo
species or some other archaic form — like H. erectus, who spread to Oceania by
1.8 million years ago._

 _. But the age of the bone has been questioned by researchers, who say the
cave's sediments may have been reworked, making the bone's layer older._

Could the bone turn out to be much older?

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DrSprout
>If humans bred only with other humans, all these markers would create a neat
phylogenetic tree, showing that human genetic diversity can be traced to a
single population that existed in Africa in the last 100,000 years.

I'm not a statistician, but from what I've studied of genetics, that seems
like an unwarranted leap. Phylogenetic trees, at the end of the day, are
guesswork (though they probably reflect reality pretty closely.) If you have a
neat phylogenetic tree, you've probably been massaging your data.

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Anon84
Other events were already known, like the "Lapedo child" in Portugal:
<http://en.wikipedia.org/wiki/Lapedo_child>

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bh42
I find the current state of that wikipedia page questionable.

 _Refutes_ is a very strong term. Humans and Neanderthals look very similar
and children have different proportions AND the differences between
individuals are great thus the inference you can make from just ONE sample
does not warrant terms like "refutes".

