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Abstract Among human and nonhuman primates, mutual eye gaze (MEG) and gaze following are believed to be important for social cognition and communicative signaling. The goals of this study were to examine how early rearing experiences contribute to individual variation in MEG and to examine the potential role of genetic factors underlying this variation. Subjects included 93 female and 23 male baboons (Papio anubis) ranging from 3 to 20 years of age. Within the sample, there were 55 mother‐reared (MR) and 61 nursery‐reared (NR) baboons. MEG was assessed in four 60‐s test sessions. For each session, the duration, frequency, and bout length were recorded. Mean values were then calculated for each individual from the four sessions. A multivariate analysis of covariance revealed an overall significant main effect for rearing. Subsequent univariate analyses revealed significant rearing effects on mean bout length, but not mean duration or mean frequency, with MR baboons having longer bout lengths compared to NR baboons. Furthermore, mean bout length was found to be significantly heritable. These results indicate that rearing experiences, and to a small extent, genetic factors, affect patterns of mutual eye gaze ‐ in particular, bout length. These results differ from previous findings in MR and NR chimpanzees, further suggesting that rearing may impact MEG in a species‐specific manner that reflects the function of gaze in different primate species. 

Abstract ObjectivesTo understand the function of food sharing among our early hominin ancestors, we can turn to our nonhuman primate relatives for insight. Here, we examined the function of meat sharing by Fongoli chimpanzees, a community of western chimpanzees (Pan troglodytes verus) in southeastern Sénégal. Materials and MethodsWe tested three non‐mutually exclusive hypotheses that have been used to explain patterns of food sharing: kin selection, generalized reciprocity, and meat‐for‐mating opportunities. We analyzed meat sharing events (n = 484) resulting from hunts, along with data on copulations, age‐sex class, and kinship to determine which variables predict the likelihood of meat sharing during this study period (2006–2019). ResultsWe found full or partial support for kin selection, direct reciprocity, and meat‐for‐mating‐opportunities. However, the analyses reveal that reciprocity and a mother/offspring relationship were the strongest predictors of whether or not an individual shared meat. ConclusionsThe results of this study emphasize the complexity of chimpanzee meat sharing behaviors, especially at a site where social tolerance offers increased opportunities for meat sharing by individuals other than dominant males. These findings can be placed in a referential model to inform hypotheses about the sensitivity of food sharing to environmental pressures, such as resource scarcity in savanna landscapes.