The Fool wrote:
From: Alberto Monteiro <[EMAIL PROTECTED]>
The Fool wrote:
Didn't native americans cross the land bridge circa 14,000 years
ago, and remained relatively unconnected to other human
populations until circa 1492?
The key word is "relatively". There is no true isolation.
I'm not buying it. There was no common ancestor as of 2000 ya or
even 3000 ya.
I am - but I think 2000-3000 is too conservative. I would bet that
_everybody_ descends from Gengis Khan, who lived less than 1000 ya.
The math is too simple: just imagine that "being a descendant of
G-K" is a disease, and that the rate of non-infected people gets
squared at each generation.
Treat semi-isolated groups with care, but once there is contact - a
single outsider f---ing a tribe woman - the group will be doomed to
be "infected" in a few generations.
Alberto--
I'm with the Fool on this one. There are too many semi-isolated
groups. The Americas were already isolated enough, I bet, so that
there are a few completely full-blooded Indians around. Aboriginal
peoples in Australia, and the New Guinea highlands were probably
more isolated genetically.
As I recall, New Guinea was split into a huge number of small
tribes, each with a bit of genetic exchange with its neighbors.
If it takes a few generations to infect a tribe, then it could
still take a long time for new genes to diffuse inland.
Genetically, I think it was that chinese people are about 8% decended
from Khan. At least that is what the last thing I read about it
said.
The Fool--
You mean something like this quote:
Research published in the American Journal of Human Genetics in 2003
suggested that 16 to 17 million men, most in Central Asia, shared a
form of the Y chromosome that indicates a common ancestor.
If so, note that it just looks at descent through the male line,
since that's what you get by analyzing the Y chromosome. This
does not count descent through females. At a guess, this increases
the number of descendants a lot, say up to 95% of everyone of Eurasian
descent.
I think your math is off. Otherwise there would be a much more even
distribution of alleles.
No, there doesn't have to be much gene flow at all for
everyone to have a recent common ancestor. This is the
gist of Alberto's argument that "one f--k can infect a
tribe". All it takes is a little bit of gene flow.
My objection is that there are a lot of groups which
were sufficiently isolated so that there has not yet
been any flow of outside genes into them to the point
of saturation. Unless you want to postulate that there
was more contact between groups than there is any solid
evidence for...
---David
Kon Tiki, Maru
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