Reply #8: Sorry - Charles Mann, published 2005

[bhikkhu]

One of the more interesting ideas, combining this author's perspective with that of "Guns, Germs and Steel", is that any isolated population develops distinct immune system variants adapted to their environment and local contagions. Then, any substantial contact between any two isolated populations leaves its mark on both populations, which we can examine in the "haplotype" record of the immune system. All indications from this are that the Americas were well isolated, and there was no substantial contact before 1492.