In-laws transformed early human society

Give it up for in-laws. Those much-maligned meddlers helped spur an ancient social revolution that propelled human groups from savannas to cities, a new study suggests.

That conclusion stems from an analysis of genealogical and marital data indicating that, among modern hunter-gatherers, monogamous sexual unions between men and women from neighboring groups create networks of in-laws that spawn widespread cooperation and cultural learning, says a team led by anthropologist Kim Hill of Arizona State University in Tempe. Social groups organized in this way distinguish humans from other primates, Hill and his colleagues propose in the March 11