Baboons Excel at Assessing Rank and Family, Study Says

March 5, 2004

Humans have an inherent ability to size up other members of their species. In a matter of minutes they assess personal attributes, like social status, and categorize one another into particular groups—family, race, or caste. Baboons, as it happens, can do much the same thing.

A recent report from researchers at the University of Pennsylvania suggests that baboons classify individuals based on rank and kinship and use this information to evaluate social interactions. The cognitive skills that allow both humans and baboons to think about social relationships could be useful for survival.

Baboons live in large social groups, and rank determines many aspects of their behavior.

A higher rank, for instance, ensures better access to resources like food, which in turn improves reproductive success. Low-ranking female baboons are known to suffer more harassment than high-ranking females; the constant irritation and bullying has been shown to cause low-ranking females stress that can eventually disrupt menstrual endocrinology, leading to infertility.

The new research suggests that being able to assess the rank of other members in the groups is important.

"You need to make judgments about when to get out of someone's way," said Robin Dunbar, an evolutionary psychologist at the University of Liverpool in the U.K. "This is particularly important for primates, because they form these little alliances, or coalitions, which can help defend them against high-ranking bullies."

Fight Recordings

Previous research had shown that baboons could distinguish members of various families. It had also shown that they knew the rank of individuals within each family.

But scientists were unsure whether baboons could simultaneously put the two facts together.

Thore Bergman, an evolutionary biologist from the University of Pennsylvania in Philadelphia, and his colleagues explored this question using a group of well-studied baboons in Botswana's Okavango Delta—the pedigree and social rank of every one of the 90 animals is known.

The researchers conducted a so-called playback experiment, in which they subjected 19 female baboons to a sequence of calls mimicking a squabble between two unrelated female members of the community. They discovered that each of the baboon's reactions depended on the rank and kinship of the baboons on the tape.

Baboon society is tremendously hierarchical. The communities are divided into several maternal lineages, or matrilines, all of which are ranked. In a community of three matrilines—A, B, and C, for example—all the females within A family outrank females in B family and C family. All females within C family are subordinate to those in A and B.

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