We humans have an innate tendency to classify others into social groups based on a variety of criteria. But researchers have been unclear as to whether we are unique in that regard. Findings published today in the journal Science suggest that baboons are skilled at keeping track of complex rules governing relationships, too.

Thore J. Bergman and colleagues at the University of Pennsylvania studied a group of more than 80 baboons in the Okavango Delta in Botswana over a period of 12 years. During this time, the researchers were able to recognize a hierarchical structure amongst the families that persisted. It was unclear, however, whether the animals had a similar interpretation of their society. To test this hypothesis, the team made recordings of a variety of sounds from known female baboons and edited them together to make it seem as though the creatures were fighting with each other. These manufactured altercations--for example, playing a threat vocalization by a high-ranking female followed by the submission squeal of a lower-ranking animal--were then played through hidden speakers while the scientists recorded the reactions of listening baboons. "Rank-reversals [in which a higher-ranking animal seemed to be submitting to a lower-ranking one] run counter to their expectations, and a baboon will momentarily pause and give a look, just as you might if you didn¿t quite believe what you had just heard," Bergman says. "Our results demonstrated that these relationships were real and relevant to these baboons." In particular, interfamilial fracases got more attention than did arguments between members of the same family.

"Humans organize their knowledge of social relationships into a hierarchical structure, and they also make use of hierarchical structures when deducing relationships between words in language," notes study co-author Robert Seyfarth. "The existence of such complex social classifications in baboons, a species without language, suggests that the social pressures imposed by life in complex groups may have been one factor leading to the evolution of sophisticated cognition and language in our pre-human ancestors."

The results of a second study published in the same issue reveal another benefit to baboon socializing: more successful mothering. Joan B. Silk of the University of California at Los Angeles and her colleagues analyzed 16 years of behavioral data from a population of baboons in Kenya. They found that baboon moms that were more social--quantified by the amount of time they spent being groomed by other adult females--had more than the average number of offspring survive to 12 months of age. (If a baboon makes it to its first birthday, the equivalent of a human child turning five, it has a good chance of surviving to adulthood and breeding, the scientists note.) Robin Dunbar of the University of Liverpool writes in an accompanying commentary that "in evolutionary terms, sociality is good for you." Something to keep in mind as the holiday party season approaches.

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