Gesture use by chimpanzees (Pan troglodytes): differences between sexes in inter- and intra-sexual interactions

Communication and social relationships are two of the most important aspects of primate life, but few studies have focused on linking these aspects in apes. There are some shared social pressures between the two sexes (e.g., kin selection, alliance formation, and protection against attack), but there are also differences (e.g., mate selection, dispersal, and social ranking systems). The aim of this study was to identify the communication strategies of the sexes with respect to their particular communication partner. I hypothesized the sexes use different strategies in their gestural communication based on their different social pressures. Specifically, males should have more positive intra-sexual relationships than females because of high focus on male-male alliance formation and maintaining high social rank, both of which directly affect their mating opportunities and relationships with all other members of the group. On the other hand, females should have more positive inter-sexual relationships due to the abuse they could receive from insubordination to males and because there is less focus on maintaining multiple, positive relationships with other females. Furthermore, because of differences in social pressures, males should have higher incidence of reassurance in same-sex interactions than females because it should be more important for males to mitigate negative interactions. I analyzed the characteristics of the gesture repertoire and frequency of gesture use for each sex in each of four contexts: (1) aggression, (2) submission, (3) greeting, and (4) reassurance. I looked at intra-sexual and inter-sexual interactions, separately. I found that, indeed, males and females utilize different strategies of gestural communication. I also found that females, but not males, have a distinct gesture strategy for communicating with the opposite sex than for the same sex. This study shows there are distinct strategies utilized by the two sexes and these differences may be explained by their differing social pressures.