In-Laws Vital to Early Human Society: Relations by Marriage Sparked Cultural Exchange, Study Says
Bower, Bruce, Science News
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 showing 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."
A social system of this type, which encourages collaboration among genetically unrelated individuals, originated about 2 million years ago as human ancestors began to hunt and gather foods that youngsters could not obtain for themselves, Hill hypothesizes. In this situation, females would have had an incentive to seek mates willing to stick around and provide food for offspring.
Monogamy began even earlier, some scientists suspect, perhaps more than 3 million years ago (SN: 6/11/05, p. 379). "Differences in social structures, not necessarily cognitive advances, allowed our species to cross the barrier to cumulative cultural evolution," says Joseph Henrich, an anthropologist at the University of British Columbia in Vancouver. …