- Face of neandethal women
I think an excellent comparable
here is the rare but occasional interbreeding that takes place between brown
bears and polar bears. It is just often
enough for us to confirm the reality but not often enough to produce special
populations and perhaps new species while we are at it.
Assuming that scenario, the once
every twenty or so years is essentially spot on.
However, I also think as human
populations expanded, that the human tribes simply outright overran the small
hunting bands subsuming the females while eliminating the males. What we need to understand is what effect
such activity would have on genetic flow.
We are actually watching this
happen in our own world in which remnant sub populations are inexorably been
absorbed into the presently vast global population. Just how much genetic contribution will any
single aboriginal population make? What
is certain is that ethnic purity is dissolving away generation after generation
for these small populations as it did for many others before them.
Knowing that would allow us to
judge the Neanderthal contribution better.
Today we have only recently discovered that it was not zero.
How often did humans and Neanderthals have carnal relations? Not very
By John
Timmer | Published about 8 hours ago
With the latest data pretty clearly showing that our ancestors had
carnal relations with some of the archaic humans they met in Asia ,
a couple of secondary questions have come up. A paper in this week's PNASattempts
to answer at least two of them: how often did this interbreeding happen, and
are we all carrying the same bits of Neanderthal DNA. The answers the authors
arrive at are "not often" and "no."
We know currently that Europeans and Asians have about two percent of
their genomic DNA that originated with Neanderthals and entered the modern
human lineage in a process called introgression. But this could have come about
several ways. For example, those regions could be the product of a single
mating that was then selected for because they improved fitness. Alternately,
matings could have been more frequent, and the two percent of the DNA that
remains is just what stuck around by chance.
To answer that question, the authors built a population/migration model,
in which they traced a modern human population that was growing and spreading
against a background occupied by Neanderthals. They could vary the degree of
interbreeding, then estimate how much DNA would remain in a modern population.
The model suggests that as few as 200 interbreeding events could leave us with
about one percent Neanderthal DNA; three percent would only require about 430
matings. If you assume that the two groups overlapped for about 10,000 years,
that works out to once every 25-50 years. So, it seems that interbreedings were
rare, which the authors ascribe to either social stigma or (more probably) a
reduced fitness or fertility in the offspring of these matings.
Their model also indicates that, with an expanding human population,
these isolated events would occur near the edge of the expansion, and the
resulting population would spread out in such a way that future generations
would end up isolated from each other. This suggests that different bits of
Neanderthal DNA would probably end up in different regional populations unless
they were selected for through evolution. We don't know whether this is the
case just yet, but the availability of Neanderthal, European, and Asian genomes
should give us a way to test the accuracy of this prediction.
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