Male baboons make friends with females for just one reason: a longer life
The benefits of companionship can mean as much as two years of extra life
The benefits of companionship for humans are well known, and they're not just confined to our mental health. Humans with strong social bonds with others live longer, healthier lives. Now a study looking at wild baboons in Africa has shown this is true for them as well. In particular, male baboons with non-sexual friendships with females live far longer than animals who lack these social bonds.
Researchers have known for years that companionship is beneficial for the health and longevity of female baboons. But because of their social structure, male baboons are much harder to study over a long term than females. Female baboons stay with their birth troop for their entire lives, and so are easy to track and observe.
Males, on the other hand, switch troops after they mature, and sometimes in adulthood as well, and so tracking them for their lifetime — which averages something like a decade and a half — can be a challenge.
But a team led by Susan Alberts, a professor of biology and chair of the evolutionary anthropology department at Duke University, was able to master this problem.
Friends with benefits
Platonic friendship among baboons of the opposite sex is, it turns out, common. According to Alberts, male baboons will frequently form non-sexual friendship bonds with females and will protect them and their offspring from aggression within the troop and from predators. The benefits of this for the females are clear.
What was less clear was the benefits of this kind of companionship for the males. The new study from Alberts and her team drew on data collected over many years from over 500 baboons at Amboseli National Park in Kenya to answer that question..
"If you compare males with the strongest bonds to those with the weakest bonds, the males [with] the weakest bonds have a 28 per cent greater risk of mortality at every age than those with the strongest bonds." Alberts said. "That's a really big difference in the mortality risk and it translates into several years of a male's life."
Close to you
Friendship in baboons involves companionship, of course. The animals will spend long periods in each others' company. But Alberts suspects that the real benefits come from something else: the time they spend grooming.
"Grooming is a really important behaviour — not only for hygienic purposes," she said. "It helps remove ticks, but also it's a way of relaxing in each other's company. A colleague of mine describes it as, 'It looks almost like they're getting a massage when they're being groomed.'"
It is also important to note that males do not groom other males.
Grooming, health and hygiene
Alberts suspects grooming likely plays a big part in the extra lifespan.
Grooming removes ticks and other parasites, which can lead to communicable diseases and blood infections. Alberts says that male baboons who aren't groomed by females are pretty obviously dirtier, and thus likely harbour more parasites in their fur.
But an important secondary benefit might be the stress-relieving effects of grooming.
Life for males in a baboon troop is very stressful. Males achieve social status in their group through a high level of often violent competition, and have to defend that status vigorously. Previous research has shown that high-status male baboons tend to live shorter lives. Alberts suspects that stress-relieving grooming has a major impact on their longevity, though she admits that so far they lack good evidence that this is true.
"We'd love to understand how the social environment gets under the skin to affect physiology and the immune system strongly enough to extend lifespan. Grooming has hygiene benefits [...] and probably what you might call psychosocial benefits — reduction in stress."
It's not entirely surprising that this kind of companionship would lead to longer, and presumably healthier lives in baboons. There have been similar findings for other species of primate, in horses, and marine mammals like dolphins and killer whales.
"The emerging picture is fairly consistent that in most but not all social animals studied so far: social bonds appear to enhance survival." Alberts said. "It really does suggest that the importance of social bonds is something that goes really deep in our evolutionary history."