Our hypothesis suggests that the absence of 7R in East Asia is recent, consequent to the establishment of powerful polities that allowed population growth and forced agricultural intensification. It is of interest in this context that 2R alleles in China are probably derived from 7R alleles by recombination, suggesting that the loss of 7R is indeed recent.

Besides lowland South America, another well known region with local anarchy and female farming is highland New Guinea. Our model of the dynamics of 7R predict that the frequency is very high in those populations. Because they have been there for tens of thousands of years and they have not moved, the Chen et al. (2) model predicts a low frequency of 7R there. This is a natural test to distinguish the two hypotheses. A 7R frequency of 0.25 was reported (2) for a sample from New Guinea, but it is not reported even in the original source of the data whether it was from a highland or coastal population.

In some societies 7R allele may lower fitness even when rare, as is probably the case in East Asia and among the !Kung Bushmen. In such populations it would stay rare even in the presence of gene flow from neighboring populations, even from neighbors with a social system that favors 7R alleles. Neutral genes would show no sharp boundary between the two populations, whereas alleles affecting behavior should show a sharp spatial gradient. This is likely to be the case with the 7R allele because some adjacent populations have very different 7R frequencies.