On 5 Jul 2006, at 12:13PM, Alberto Monteiro wrote:
David Hobby wrote:
I'm with the Fool on this one. There are too many semi-isolated
groups.
Yes - and the key word here is *** semi ***
The Americas were already isolated enough, I bet, so that
there are a few completely full-blooded Indians around.
It depends on how you define a full-blooded Indian.
Aboriginal peoples in Australia, and the New Guinea highlands
were probably more isolated genetically.
But not absolutely isolated. They didn't migrate to the
Nazi Moon Base or to the Hollow Earth. They kept contact
with some neighbouring tribe.
As I recall, New Guinea was split into a huge number of small
tribes, each with a bit of genetic exchange with its neighbors.
So here you have it: there's no way this semi-isolation can
protect the tribe.
If it takes a few generations to infect a tribe, then it could
still take a long time for new genes to diffuse inland.
Yes. But 500 years or about 15 generations is time enough.
Exactly. If neighbouring tribes interbreed (as they do) then the
chain reaches all the way to the coasts where the immigrants are in a
few generations. Only a small group that was completely isolated and
completely without exogamy could avoid sharing common descent. And
such groups become extinct because of inbreeding so they don't count.
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.
100%, with 99.999% certainty :-P
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...
Ok, so let's do the math. Let's create a simulation model,
splitting a human population of 1 Giga into 100-member
tribes [easy enough for modern computers], spread these tribes
all over the globe, create a rule of cross-contamination
[two neighbouring tribes exchange one member each generation -
a consertavite estimate], and add an extra random exchange
from each costal tribe to a random European tribe after 1500.
That's more or less what the researchers quoted in the article at the
start of this thread did to get the results they got...
--
William T Goodall
Mail : [EMAIL PROTECTED]
Web : http://www.wtgab.demon.co.uk
Blog : http://radio.weblogs.com/0111221/
And yes, OSX is marvelous. Its merest bootlace, Windows is not worthy
to kiss. - David Brin
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