October 2, 2012
Baboon Personality Plays Role In Health, Long Life
April Flowers for redOrbit.com - Your Universe Online
It's important to have friends, whether you are human or baboon. Studies have shown that strong social networks lead to better health and longer lives for both species. In a new study, researchers from the University of Pennsylvania and Arizona State University have shown that baboon personality plays a role in these outcomes. Like people, some baboons have personalities better suited to making and keeping friends than others.
The Penn researchers have been observing a group of baboons living in the Moremi Game Reserve in Botswana for the last 17 years, studying the biological roots of their social dynamics. Baboon society is extremely hierarchical, with females "inheriting" their dominance rank from their mothers and enjoying priority access to food and mates.
When it comes to evolutionary success, though, a high dominance rank just doesn´t explain everything because these females do not have greater reproductive success than lower-ranked females.
Robert Seyfarth, psychology professor at the University of Pennsylvania said: "If you look at a baboon society and see the ranked, matrilineal families, you would think that whatever traits put an individual at the top of the hierarchy, that's what natural selection is going to favor. But that turns out not to be the case."
"In fact, dominance rank is not as good a predictor of reproductive outcomes as a close network of social relationships and stable relationships over time. So our question became 'What predicts having a strong network?'"
The study, published in the Proceedings of the National Academy of Sciences (PNAS), states that all female baboons actively work to maintain close social bonds. Like humans, some are more successful than others. The research team wanted to understand this variation because these traits seem closely tied to fitness and reproductive success.
The research team measured individual female baboons on their sociability based on a number of factors. The baboons were observed in their natural habitat as the scientists measured the number of grooming partners each had, and their tendency to be friendly or aggressive towards others. The team also looked at the reproductive and fitness benefits the females accrued, including how long they and their offspring lived, and the stress levels that were revealed in hormones present in scat.
Social bonding was not fully predictable by dominance rank or the size of the family a female was born into.
"Even when a female has a lot of relatives," Professor Dorothy Cheney of the University of Pennsylvania noted, "sometimes she's a loner, but some females who have no relatives do just fine. It suggests that you have to be both lucky and skilled to have these networks."
These social skills come down to individual personality traits, the study found. To determine a female's personality, the team listened to grunting behaviors. In baboon society, grunting greases the social wheels between females. A lower ranking female will grunt when approaching one of higher rank as appeasement to avoid aggressive behavior. A higher ranking female will sometimes grunt to a lower ranking female to put her at ease, and females of any rank grunt when approaching a mother with a baby so that she will allow them to interact with the baby.
The baboons were classified into three distinct personality groups: "nice," "aloof " and "loner."
The study found that nice females were friendly to all others, often grunting to lower ranked females to put them at ease. These females formed strong, long lasting social bonds with fairly consistent partner preferences.
Baboon females labeled as aloof were more aggressive and less friendly than the nice ones. Mostly they grunted to higher ranking females who had infants. For the most part, they had weaker social bonds but still had consistent partner choices.
Loner females are relatively unfriendly and very aggressive, grunting mostly to appease higher ranking females without infants. The social bonds they form are weak with constantly changing partners.
Comparatively, loner females had higher stress levels, weaker social bonds and the least stable social partners. This correlated with lower offspring survival and shorter lifespans. Nice and aloof females showed health and reproductive benefits associated with strong social bonds.
"This belies the idea that everything is competition and conflict," Cheney said.
The researchers aren't sure what the mechanics of being "nice" or "aloof" are, but it's clear that cooperative personalities are adaptive.
"These results have allowed us to, for the first time in a wild primate, link personality characteristics, social skill and reproductive success," Seyfarth said. "By being a nice baboon, you increase the likelihood of having strong social bonds, which in turn translates to a better chance of passing on your genes."