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. >> 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. Alberto Monteiro _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
