Primate rituals: The function of greetings between male Guinea baboons

The bond-testing hypothesis suggests that social animals can obtain honest information about the quality of their dyadic relationships by exchanging costly, high-risk signals (Zahavi & Zahavi 1997). We evaluated this hypothesis by investigating whether adult male baboons use intense greeting interactions to test the quality and strength of their social bonds. Intense greetings involve intimate and risky behaviors such as embracing and the diddling of the penis and/or scrotum. Data were collected on a colony of 40 Guinea baboons (Papio papio) at the Brookfield Zoo in Chicago. Fifteen adult male baboons were focally observed for 30-min sessions over a 6-mo period, resulting in 195 h of observation. We assessed the quality of male-male relationships using measures of affiliation, aggression, and social tolerance. As predicted by the bond-testing hypothesis, dyads with strong social bonds exchanged a higher frequency of intense greetings than did pairs with poor relationships. We found no support for the competing hypotheses, that suggest that greetings have an aggressive or submissive function or are used as a form of post-conflict reconciliatory behavior. Neither dominance relationships nor contextual variables were predictive of intense greeting patterns. We suggest that by imposing on his partner, a male baboon is able to obtain reliable information about this individual's current willingness to cooperate and invest in the relationship.