Abstract
The meat-for-sex hypothesis posits that male chimpanzees ( Pan troglodytes) trade meat with estrous females in exchange for short-term mating access. This notion is widely cited in the anthropological literature and has been used to construct scenarios about human evolution. Here we review the theoretical and empirical basis for the meat-for-sex hypothesis. We argue that chimpanzee behavioral ecology does not favor the evolution of such exchanges because 1) female chimpanzees show low mate selectivity and require little or no material incentive to mate, violating existing models of commodity exchange; and 2) meat-for-sex exchanges are unlikely to provide reproductive benefits to either partner. We also present new analyses of 28 years of data from two East African chimpanzee study sites (Gombe National Park, Tanzania; Kanyawara, Kibale National Park, Uganda) and discuss the results of previously published studies. In at least three chimpanzee communities, 1) the presence of sexually receptive females did not increase hunting probability, 2) males did not share preferentially with sexually receptive females, and 3) sharing with females did not increase a male's short-term mating success. We acknowledge that systematic meat sharing by male chimpanzees in expectation of, or in return for, immediate copulations might be discovered in future studies. However, current data indicate that such exchanges are so rare, and so different in nature from exchanges among humans, that with respect to chimpanzees, sexual bartering in humans should be regarded as a derived trait with no known antecedents in the behavior of wild chimpanzees.
Highlights
In this paper we review published articles and provide new data on the influence of female sexual state on hunting and meat sharing among chimpanzees (Pan troglodytes) to review the ‘meat-for-sex’ hypothesis
Meat-for-sex exchanges among chimpanzees are often treated as a well-established, species-typical phenomenon (e.g. Radetsky, 1995; Bird, 1999; Hawkes and Bird, 2002; Shlain, 2003; Bunn, 2007; Lovejoy, 2009), and they provide the basis for various speculations about the evolution of human sexual behavior (e.g Lovejoy 2009)
We note that female chimpanzees rarely require material incentives to mate, and that amid the competitive mating system of chimpanzees, the potential effects of such incentives on the reproductive success of either partner are insufficient to drive the evolution of meat sharing, at the low rates reported from East African sites
Summary
In this paper we review published articles and provide new data on the influence of female sexual state on hunting and meat sharing among chimpanzees (Pan troglodytes) to review the ‘meat-for-sex’ hypothesis. Based on the available evidence, it is likely that female mate preferences have a weak overall influence on male reproductive outcomes in chimpanzees in comparison with the forces of male aggressive competition, sexual coercion and sperm competition, suggesting that sharing meat with the occasional reluctant female would do little to increase a male’s reproductive success This conclusion is reinforced by the fact that male meat possessors are usually high-ranking While these data suggest that there might be a positive short-term effect of sharing on mating, the difference was not statistically significant after controlling for repeated observations of dyads (P = 0.2) To examine this question further, we identified all instances (between 1995 and 2005) at Gombe (N = 24) when a focal swollen female received meat from a male, and asked whether the male was more likely to mate with that female after sharing occurred than before. Data from Gombe, Ngogo and Kanyawara do not support the prediction that short-term male mating success is correlated with sharing (Table 1)
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