for National Geographic News
A new report shows how genes can help reveal how societal rules affect mobility. The genetic study focused on traditional tribes in Thailand and found that in some societies, many more women than men migrated for marriage. One explanation is that men have been keeping non-related men out of their villages.
The findings raise questions about how society structure can impact genetic diversity in certain locations. This kind of research may also lead to the use of genetic analysis to determine early society structure.
The researchers studied six traditional populations in northern Thailand to determine the effect social organization has on the migration patterns of men and women.
Three of the groups were patrilocal societies, societies where married couples move to the husband's village. Three more groups were matrilocal, societies where married couples typically live in the wife's village.
The researchers found that the two societal arrangements result in significantly different postmarital migration patterns, despite the fact that the groups are all agriculturally based and live in the same geographic region.
"What we find is that in the patrilocal societies, the females are moving much, much more than the males are," said Laurent Excoffier, a population geneticist at the University of Bern in Switzerland.
"In matrilocal society males are moving a bit more than females, but it is not at a rate that is statistically significantessentially the males and females are moving at about the same rate. It's clearly different from what is happening in the patrilocal society."
The hill tribes studied included the Ahka and two groups of Lisu, representing a patrilocal society. The Lahu, Red Karen, and White Karen represented matrilocal societies.
All six groups are agricultural, hacking a difficult livelihood out of marginal lands in the isolated backcountry of Thailand.
The study showed that, in patrilocal societies, 15 times more women than men were being exchanged among these neighboring populations.
"Our findings raise interesting questions about what is controlling male-versus-female migration in these groups," said Mark Stoneking, an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Germany.
"The fact that the matrilocal groups are fairly loose and that, even though they prefer that males migrate to the residence of the female, there's obviously a lot of female migration still going on. ... In patrilocal groups they've basically completely shut down the migration of males between groups. [That] is compatible with the hypothesis that men are strictly controlling male immigration in patrilocal societies."
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