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A sense of fairness plays a critical role in supporting human cooperation (1-3). Adult norms of fair resource sharing vary widely across societies, suggesting that culture shapes the acquisition of fairness behaviour during childhood (4,5). Here we examine how fairness behaviour develops in children from seven diverse societies, testing children from 4 to 15 years of age (n = 866 pairs) in a standardized resource decision task (6,7). We measured two key aspects of fairness decisions: disadvantageous inequity aversion (peer receives more than self) and advantageous inequity aversion (self receives more than a peer). We show that disadvantageous inequity aversion emerged across all populations by middle childhood. By contrast, advantageous inequity aversion was more variable, emerging in three populations and only later in development. We discuss these findings in relation to questions about the universality and cultural specificity of human fairness., Fairness requires a concern for relative payoffs between oneself and others or between third parties. A key component of the human sense of fairness is inequity aversion, defined as the [...]

The hypothesis that chimpanzee meat-eating is a luxury, made possible by high energy abundance in the plant diet, has been supported to date by comparisons of hunting seasons within sites, particularly at Ngogo (Kibale National Park, Uganda). Here I explore why chimpanzees hunt rarely in Kanyawara (Kibale). Differences ate particularly striking between Kanyawara and Ngogo, two communities separated by only 10 km and occupying forests of similar structure, with prey density somewhat higher in Kanyawara. Kanyawara data come from 13 years of daily observation, including detailed study of monkey-chimpanzee encounter rates over 29 months. Ngogo data come from studies by J. Mitani and D. Watts. Daily rates of encounter between chimpanzee parties and groups of red colobus were similar in the two communities (0.42 - 0.50 encounters per day). However, Kanyawara chimpanzees were less likely to hunt (15% of encounters, compared to 37% at Ngogo), they were less successful (47% of hunts led to a kill, compared to 84% at Ngogo), and they killed fewer prey per hunt (2.1, compared to 4.2 at Ngogo). The low rate of predation at Kanyawara is attributed not only to the fewer number of males in the community at Ngogo, as proposed by Mitani and Watts (2002), but also to lower fruit availability in Kanyawara, as well as relatively intense aggressive responses by red colobus monkeys. This study suggests that greater plant food availability promotes hunting in comparisons both within and between populations.

The occurrence of fatal attacks during intergroup encounters among chimpanzees suggests that certain aspects of chimpanzee and human intergroup aggression may be explicable in similar ways. This paper addresses three questions: What conditions favor the evolution of lethal raiding in intergroup aggression? Why is intergroup aggression in these two species predominantly the domain of males? Under what circumstances do groups compete over access to females as opposed to material resources? Examination of comparative data on nonhuman primates and cross-cultural study of foraging societies suggests that attacks are lethal because where there is sufficient imbalance of power their cost is trivial, that these attacks are a male and not a female activity because males are the philopatric sex, and that it is resources of reproductive interest to males that determine the causes of intergroup aggression. [ABSTRACT FROM AUTHOR]