Wild Chimpanzees Exchange Meat for Sex on a Long-Term Basis

Abstract

Humans and chimpanzees are unusual among primates in that they frequently perform group hunts of mammalian prey and share meat with conspecifics. Especially interesting are cases in which males give meat to unrelated females. The meat-for-sex hypothesis aims at explaining these cases by proposing that males and females exchange meat for sex, which would result in males increasing their mating success and females increasing their caloric intake without suffering the energetic costs and potential risk of injury related to hunting. Although chimpanzees have been shown to share meat extensively with females, there has not been much direct evidence in this species to support the meat-for-sex hypothesis. Here we show that female wild chimpanzees copulate more frequently with those males who, over a period of 22 months, share meat with them. We excluded other alternative hypotheses to exchanging meat for sex, by statistically controlling for rank of the male, age, rank and gregariousness of the female, association patterns of each male-female dyad and meat begging frequency of each female. Although males were more likely to share meat with estrous than anestrous females given their proportional representation in hunting parties, the relationship between mating success and sharing meat remained significant after excluding from the analysis sharing episodes with estrous females. These results strongly suggest that wild chimpanzees exchange meat for sex, and do so on a long-term basis. Similar studies on humans will determine if the direct nutritional benefits that women receive from hunters in foraging societies could also be driving the relationship between reproductive success and good hunting skills.

Cooperation and competition in chimpanzees: Current understanding and future challenges

“…66 While the preceding findings do not support the hypothesis that male chimpanzees share meat with females to improve their mating success, a recent study from the Taï National Park suggests otherwise. 96 Observations made there indicate that males copulated more frequently if they shared meat with females than if they did not. This relationship persists after controlling several potential confounding variables, including male dominance rank, the amount of time males and females spent together, and female age, gregariousness, and frequency of begging.…”

“…3). 66,84,[94][95][96] At first glance, meat sharing is one of the most perplexing facets of chimpanzee behavior. Meat, after all, is an extremely valuable resource, packed with valuable micronutrients that are not easily obtained elsewhere, 41,97 making it highly prized by all individuals.…”

Chimpanzees return favors at a personal cost

“…In their natural habitats, chimpanzees-human's closest living evolutionary relatives together with bonobos (Pan paniscus) (5)-also engage in a number of cooperative activities, such as teaming up with partners in fights, grooming with others reciprocally, and even sharing meat after successful hunts (6)(7)(8)(9)(10). Observational studies with captive animals have shown further that, over the long-term, chimpanzees reciprocally groom and share food with others (11)(12)(13)(14).…”

Production of food-associated calls in wild male chimpanzees is dependent on the composition of the audience

“…High and equitable grooming rates between two partners are related to strong social bonds (Fedurek and Dunbar 2009) and other social phenomena, such as increased coalitionary support during intra-group aggression (Hemelrijk and Anneke 1991) and increased food sharing (de Waal 1997). Although the evidence for reciprocal interchange of different services in chimpanzees is mixed (Gomes and Boesch 2009;Gilby 2006;Mitani and Watts 2001;Schino and Aureli 2009), it is possible that food call production may be a 'currency' that is exchanged amongst individuals for other services.…”