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Variation in male mating success is often related to rank differences. Males who are unable to monopolize oestrous females alone may engage in coalitions, thus enhancing their mating success. While studies on chimpanzees and dolphins suggest that coalitions are independent of kinship, information from female philopatric species shows the importance of kin support, especially from mothers, on the reproductive success of females. Therefore, one might expect a similar effect on sons in male philopatric species. We evaluate mating success determinants in male bonobos using data from nine male individuals from a wild population. Results reveal a steep, linear male dominance hierarchy and a positive correlation between dominance status and mating success. In addition to rank, the presence of mothers enhances the mating success of sons and reduces the proportion of matings by the highest ranking male. Mothers and sons have high association rates and mothers provide agonistic aid to sons in conflicts with other males. As bonobos are male-philopatric and adult females occupy high dominance status, maternal support extends into adulthood and females have the leverage to intervene in male conflicts. The absence of female support to unrelated males suggests that mothers gain indirect fitness benefits by supporting their sons.

Primate individuals use a variety of strategies in intergroup encounters, from aggression to tolerance; however, recent focus on the evolution of either warfare or peace has come at the cost of characterizing this variability. We identify evolutionary advantages that may incentivize tolerance toward extra‐group individuals in humans and nonhuman primates, including enhanced benefits in the domains of transfer, mating, and food acquisition. We highlight the role these factors play in the flexibility of gorilla, chimpanzee, bonobo, and human behavior. Given humans have an especially broad range of intergroup behavior, we explore how the human foraging ecology, especially large spatial and temporal fluctuations in resource availability, may have selected for a greater reliance on tolerant between‐community relationships—relationships reinforced by status acquisition and cultural institutions. We conclude by urging careful, theoretically motivated study of behavioral flexibility in intergroup encounters in humans and the nonhuman great apes.

In primates, age, sex, and social status can strongly influence access to food resources. In Pan, these criteria are assumed to influence access to vertebrate meat. However, the significance of meat in terms of its role in the nutrition of Pan is still debated. Here we present a study using stable carbon and nitrogen isotope ratios in hair samples from habituated, wild bonobos (Pan paniscus) to explore these issues. Over a period of 5 mo hair samples were collected from fresh bonobo nests at LuiKotale, Democratic Republic of Congo. Hair samples were assigned to known individuals and were of sufficient length to allow the evaluation of isotopic variation over several months. Samples of plant foods and sympatric fauna were also analyzed. The δ 13 C and δ 15N results of the bonobo hair were remarkably homogeneous over time and for the group as a whole. There are no differences in diet between the sexes. Within the group of males, however, there was a positive correlation between dominance status and δ 15 N. The isotopic data indicate that the contribution of fauna to bonobo diet is marginal and that plant food is the dietary protein source. In only some cases did elevated δ feeding ecology | great apes R econstructing hominin diets and possible meat-eating behavior is a key research area in the field of human evolution (1, 2) because adaptations for the consumption of animal protein and fat have been related to brain developmental trends in the evolution of the human lineage (3). As our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) are often used as referential models in the context of diet composition, feeding behavior, and food processing (4, 5). The diet of both Pan species is dominated by plant foods: fruits account for more than 50% of the daily dietary intake and are complemented by leaves, herbs, and, at least in some populations, underground storage organs. Both species supplement their plant diet with insects and meat from vertebrates acquired by hunting (6). Behavioral observations from meat-eating events suggest that both Pan species consider meat a highly attractive food; meat is generally considered to be a high-quality food resource that offers nutrients that are difficult to obtain from other foods (7). Conflicts among those who compete for access to meat are frequent, and dominant individuals may take carcasses from subordinates. Longitudinal data from one population suggest that meat consumption by female chimpanzees can shorten interbirth intervals (8). Given the close link between the nutritional status of females and reproductive success, the inferred nutritional function of meat eating seems plausible, but requires further exploration. Although existing evidence demonstrates that meat is part of the diet of most or all Pan populations, how meat consumption relates to the overall diet remains unknown (7). Hunting and meat eating is less frequently observed in bonobos (Pan paniscus) compared with some chimpanzee populations (9). Observational data from two sit...

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The two closest living relatives of humans, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), share many traits that are common in humans but rare in other mammals, including societies with high fission–fusion dynamics, male philopatry, female dispersal and extensive social bonding among unrelated individuals [1] . The major difference between these two species is that male aggression is more frequent and intense in male-dominated chimpanzees than in bonobos, where the highest-ranking individuals are female [1] . One potential explanation is that because periods of female sexual receptivity and attractiveness are more extended in bonobos [2] , males compete less intensely for each mating opportunity. This would reduce the strength of selection for traits that lead to success in direct contest competition between males and in sexual coercion of females, thus increasing the potential for female choice [3] . Accordingly, it has been predicted that the influence of male dominance rank on reproductive success and the extent of male reproductive skew should be lower in bonobos than in chimpanzees [1] . Although relevant for understanding the evolution of the unusual levels of egalitarianism and cooperation found in human hunter-gatherers [4] , comparative analyses in the genus Pan have been limited by the scanty paternity data available for wild bonobos [5] . Here, we show using the largest sample of paternity data available that, contrary to expectation, male bonobos have a higher reproductive skew and a stronger relationship between dominance rank and reproductive success than chimpanzees