On 07/07/2006, at 12:55 AM, David Hobby wrote:
I'm not arguing against a figure of 10,000 years, that's a long time.
Alberto and others were pushing for a much lower figure, around 1000
years, for EVERYONE to share ancestry from some person who lived then.
Were they? I thought the common ancestor, as being pushed by the
paper, was "a few thousand years ago". 4 - 6 thousand. It's a
statistical study, but what it suggests is very plausible.
...
limits). Or do you really think you had 2,147,483.648 *individual*
ancestors 30 generations ago? No, of course not - family trees
converge as well as diverge.
Yes, I've got that point. In one big homogeneous population, you
don't have to go back that far before everyone has exactly the same
ancestors. My point is that until quite recently, the World was
NOT an homogeneous population.
It doesn't matter - as i showed in another post, even the smallest
amount of interbreeding means that there is ancestry, even if there's
little measurable genetic relatedness in the main chromosomes.
Third, totally isolated populations tend
to die out.
You mean because of genetic drift, or what?
No, inbreeding.
I imagine that
would take awhile. Couldn't a population of a few hundred
be isolated for over 1000 years and survive? (Again, I'm
not taking issue with the general argument. I just feel that
1000 or 2000 years is too small a number.)
Maybe so. But a couple of theoretically totally isolated populations,
even isolated for a thousand years - where did they come from? and
even if the paper is wrong, and it's not *all* humanity alive today,
it's all bar one group in a mountain somewhere, the point is hardly
changed.
...............................................................
Here's a candidate group with "low cross-contamination probability",
the native inhabitants of North Sentinel Island in the Bay of Bengal.
Here's a quote, from: http://en.wikipedia.org/wiki/Sentinelese
The Sentinelese remain skeptical and generally hostile to any
approaches from outsiders.
In 2006, Sentinelese archers killed two fishermen who were fishing
illegally within range of the island, and drove off the helicopter
that was sent to retrieve their bodies with a hail of arrows.
Living on a worthless island and shooting arrows at everyone
who approaches seems to reduce the likelihood of interbreeding
with outsiders. : )
They are probably not the best example, since they have been
directly exposed to outsiders from the sea for ages. But I
like their style, and their case is well known.
Their are other candidate groups. Google "uncontacted peoples".
You seem to have trouble grasping the timescales here. It's a very
common problem when talking evolution.
Charlie
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