Baboon Studies Reveal Pressures And Benefits Of Complex Social Societies

Two recent studies of African baboons provide new insights into the complexity of monkey social behavior. This research may in turn reveal the conditions that contributed to the evolution of distinctly human traits, such as language and certain strategies for survival. Both studies are to be published in the November 14 issue of the journal Science and received support from The Leakey Foundation.

It is accepted that humans routinely classify others according to their individual attributes, such as status or wealth. We all know that we classify others according to what groups they belong to in society – Republicans, Red Sox fans, the 'Bloods", and so on. The ability to classify others by membership in a group, maybe even more than one group, requires a lot of computing power – brainpower - and may even require language. Until now, we have not known whether such complex group classifications are uniquely human, or whether animals do it too.

To investigate this question, scientists from the University of Pennsylvania have studied a group of more than 80 baboons in Botswana's Okavango Delta since 1992. Baboon groups are organized around a rank hierarchy of matrilineal families. At the top of the rank order is the matriarch of the highest-ranking family, followed in descending rank order by her offspring, then the highest-ranking female in the next family followed by her offspring, and so on. Experiments conducted in 1995 and 1999 showed that baboons recognize both the rank and the kinship relations among others. Now the University of Pennsylvania team wanted to test whether baboons -- like humans -- could combine their knowledge of kinship and rank into a genuine hierarchical structure based on both social rules simultaneously.

To do this, Dorothy Cheney, Robert Seyfarth and their colleagues Thore Bergman and Jacinta Beehner designed an experiment for baboons in Botswana's Okavango Delta in which they played to a wild female a sequence of calls mimicking a fight between two other females. The listening females' reactions showed that they knew not only which individuals were fighting, but which families they belonged to, whether dominant or subordinate.

These experiments have demonstrated for the first time that animals other than humans classify members of their community simultaneously according to both individual attributes and membership of a societal group. The selective pressures imposed by complex societies may therefore have favored cognitive skills that constitute an evolutionary precursor to human cognition, and may inform theories concerned with the evolution of human language.

In a second new study, also of baboons, sixteen years of behavioral data on a well-studied population of baboons in Amboseli, Kenya demonstrates that friendliness pays! Friendly mothers raise their infants more successfully than do unfriendly mothers. The social bonds of adult female baboons -- typically characterized by frequent grooming, close spatial proximity, and occasional acts of coalitionary support -- are an important component of variation in female lifetime fitness. For example, close association with other group members may reduce stress levels of infant and mother alike. Alternatively, close association with other group members may provide mother and infant with direct material benefits, such as protection from harassment or access to valuable resources.

Together, the two studies show that natural selection has favored a sophisticated social intelligence in primates -- social intelligence that improves a baboon female's reproductive success and may help us to understand the evolution of intelligence in humans. The roots of human sociality extend far back into our primate roots.

###

The Leakey Foundation is an international membership committed to research related to human origins, behavior and survival.