Baboon females actively work to maintain close social bonds but, like humans, some seem to be better at it than others. With the strength of baboons’ social network closely tied to their health and reproductive success, a team of Penn researchers wanted to get at the root of this variation. What they found is that, just like in humans, it’s a question of personality.  

Robert Seyfarth, a professor in the Department of Psychology, and Dorothy Cheney, a professor in the Department of Biology, along with their colleagues and students, have spent the last 17 years observing a group of baboons living in the Moremi Game Reserve in Botswana, studying the biological roots of their social dynamics.  

Over a seven-year period, the researchers measured individual female baboons on their sociability by counting the number of grooming partners a baboon had, as well her tendency to be friendly or aggressive toward others. They also observed fitness measures: how long individuals and their offspring lived, as well as their stress levels, as determined by the presence of certain hormones in their droppings.

Baboons live in hierarchical societies, where females “inherit” their dominant ranks from their mothers. But the researchers found that the strength of an individual’s social bonds was not fully predicted by a female’s rank or the size of the family she was born into.   

“Even when a female has a lot of relatives,” Cheney says, “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.”

Like humans, these skills came down to individual personality traits.

To determine a female’s personality, the researchers paid close attention to grunting behavior. Lower-ranking females will grunt to higher-ranking females as an act of deference, but a higher-ranking female may choose to be friendly: grunting to a lower-ranking one to put her at ease.

Working from the trends they found in the baboon’s behavior, the researchers grouped the baboons into three distinct personality profiles: “nice,” “aloof,” and “loner.”

Of the three, the "loners" had the highest stress levels, the weakest social bonds, and the least stable social partners over time. Both of these measures were correlated with lower offspring survival and shorter lifespans.

Both the "nice" and "aloof" females showed the health and reproductive benefits associated with strong social bonds. 

“These results have allowed us to, for the first time in a wild primate, link personality characteristics, social skill, and reproductive success,” Seyfarth says. “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.”