Chimps reap what they groom.

Chimps reap what they groom

A chimpanzee doesn't spread nasty rumors or call a lawyer if it grooms the hair of friend who then refuses to return the favor by forking over a few bananas at mealtime. Nonetheless, chimps enforce specific rules about social obligations that show a link to the far more complex notions of fairness and justice held by humans, asserts Frans de Waal of Emory University in Atlanta.

"Violations of reciprocity or expected behavior elicit moralistic aggression among chimpanzees ... that [is] recognizable as a root of the human anger in response to perceived injustice," he contends.

Studies of food sharing by chimps at Atlanta's Yerkes Regional Primate Research Center offer a case in point. When caretakers arrive with food, the animals first hoot and jump about in a kind of dance. This "celebration" serves to reduce tension and reaffirm the group's hierarchy of dominant and submissive members, de Waal says.

Negotiations over food distribution then begin, as chimps who want food approach those with enough to share. Food changes hands about half the time; the rest of the requests get rejected. Chimps most often get food from individuals whom they have groomed that day, de Waal maintains. Dominant males are among the most generous with their food, he notes. Fights occur rarely and usually stem from attempts either to take food without having performed grooming services or to withhold food after receiving grooming.

Chimps usually kiss, hug, or otherwise make peace after a fight, especially if they need help and cooperation from one another in the future, according to de Waal.

"Social rights aren't inborn," he argues. "In primates, rights result from negotiations between individuals."