The more time wild female baboons spend in the company of other adult baboons, particularly while occupied with grooming activities, the more likely their offspring are to live until their first birthday, the team reports in the Nov. 14 issue of Science.
"Until now, social scientists assumed that because females invest a lot in social relationships, they must gain a lot from those relationships, but we've never been able to make a direct link to reproductive success," said Joan B. Silk, the study's lead author. "These findings provide the first evidence that there's a link between the amount of social involvement and having offspring who survive the critical first year of life."
The connection is noteworthy because "reproductive success is the gold standard in evolutionary biology," said Silk, an anthropology professor in UCLA College. "A trait can't really be determined to have an evolutionary advantage unless it has a positive impact on reproductive performance. Socializing and grooming are traits that help baboons pass along their genes."
Along with evolutionary biologists from Duke and Princeton Universities, Silk pored over 16 years of data collected in Kenya's Amboseli Basin, which is located at the foot of Mt. Kilimanjaro. Since 1984, researchers have measured the social behavior of more than 100 wild savannah baboon females, recording daytime activities six days a week in 10-minute intervals.
Among the resulting 34,000 records of discrete activities, Silk's team looked for examples of social behavior among female baboons, including the propensity to spend time within at least 15 feet of another adult and to groom other females or to allow other females to pick dirt, ticks and other parasites from their own hair.