Some baboons groom their buddies for long lives.
Female chacma baboons that maintain close, lasting friendships live considerably longer than their peers who switch companions more frequently, a new study finds.
Though high-ranking females generally outlive their lower-ranking peers, close friendships marked by frequent and prolonged bouts of mutual grooming boost longevity even more than elevated social status, anthropologist Joan Silk of the University of California, Los Angeles and her colleagues report in a paper published online July 1 in Current Biology.
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It’s a classic tale of underdogs — or in this case undermonkeys — beating the odds. Subordinate female baboons can offset threats to their survival by building solid friendships that help them outlive many of their social superiors, the scientists suggest.
“Our findings are strikingly similar to evidence from humans showing that social ties have important effects on our mental and physical health, and on longevity,” Silk says.
Intriguingly, keeping friends, not making new ones, boosts longevity for female chacmas in the new study, remarks biopsychologist Barbara Smuts of the University of Michigan in Ann Arbor. That fits with other studies indicating that close friendships in various primate species foster survival and reproductive success (SN: 12/20/03, p. 397).
It’s not clear how having a few close female friends lengthens a female chacma’s life, Smuts says. In humans, having a dependable network of friends appears to soften the impact of stressful events on heart, hormone and immune responses.
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Mutual stress reduction among female baboon friends may make it easier for them to notice predators and make fast escapes, Smuts speculates. Or, friends might take turns looking out for predators and warning each other of danger.
Females able to make lasting friends may spend more time resting and foraging near other baboons, reducing their vulnerability to predator attacks, Silk adds.
Regular grooming among good friends also rids them of parasites that cause health problems, notes Stanford University biologist Robert Sapolsky.
“It all depends on what causes the death of female baboons, which is hard to determine because there’s seldom a single cause,” comments New York University anthropologist Clifford Jolly. Predators often target baboons already weakened by infection, malnutrition, arthritis or other infirmities, he says.
Silk and her colleagues studied 44 adult female chacma baboons. These animals spent at least two years in a baboon group in the African nation of Botswana that was tracked from 2001 to 2007 as part of work led by biologist and long-term project director Dorothy Cheney of the University of Pennsylvania in Philadelphia. For each female baboon, the researchers identified her other regular grooming partners during the observation period.
Beginning in baboon middle-age, around age 8, a longevity advantage appeared for females with a few particularly close, consistent friendships. That advantage increased as years passed. Females that survived to old age typically had formed moderately or extremely strong friendships — assessed mainly by the frequency and duration of mutual grooming episodes — during the study.
Adult male chacmas never groom each other, because they change groups one or more times and constantly compete for mates, Jolly says. Chacma males briefly groom females, usually to initiate sex. Males in other baboon species engage in mutual grooming, raising the possibility that they also derive health benefits from enduring friendships, Jolly adds.