By Bruce Bower
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 Science.
“Alliances between foraging groups are facilitated because unrelated males all associate with the same female, who may be their daughter, sister, wife, mother or daughter-in-law,” Hill says. “By friendly association with her, males begin to associate with each other.”