Like humans, baboons with good friends often enjoy better health and longer lives. Now research suggests the strength of a baboon's social circle depends less on its rank than its personality -- and being nice pays off.
"These results have allowed us to, for the first time in a wild primate, link personality characteristics, social skill and reproductive success," researcher Robert Seyfarth, of the University of Pennsylvania, said in a statement. "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."
In baboons' hierarchical societies, females inherit their rank from their moms, which determines their access to food and mates. But a higher rank and a bigger network of kin does not always lead to greater fitness and reproductive success, the researchers said.
"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," Seyfarth explained. "So our question became 'What predicts having a strong network?'"
Seyfarth and his fellow researchers observed 45 female baboons in the Moremi Game Reserve in Botswana over the course of seven years, paying close attention to each baboon's friendly or aggressive tendencies. The team also studied how long the baboons and their offspring lived and measured their stress levels by testing their droppings for certain hormones. Based on trends they saw in the baboons' behavior, the researchers lumped the females into three personality groups: "nice," "aloof" and "loner."
Nice baboons were friendly to all others regardless of status -- they even reassured lower-ranking peers with grunts -- and they formed strong social bonds with long-term grooming partners. Aloof females also had consistent grooming partners as well, but they formed slightly weaker bonds and were more aggressive to others, often reserving their grunts for higher-ranking females with infants. Both nice and aloof females had the health and reproductive benefits associated with strong social bonds, the researchers said.
Meanwhile, loner females were the least friendly and formed the weakest social bonds. They often changed grooming partners and typically grunted only to appease higher-ranking females without infants. This personality type was linked to higher stress levels, lower offspring survival and shorter life spans, the researchers found.
The study, published Monday (Oct. 1) in the Proceedings of the National Academy of Sciences, leaves some questions unanswered, including: Why would any female adopt the "loner" strategy? Even though a low social status and a lack of kin could exacerbate loner tendencies, the researchers found some loners did have close kin around while other females in the nice group did not.
"If Loners are often the victims of circumstances, what skills or motivation allow some individuals to overcome these circumstances while others do not?" the researchers asked in their study.
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