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In suggesting that new nations often coalesce in the decades following war, historians have posed an important psychological question: Does the experience of war generate an enduring elevation in people's egalitarian motivations toward their in-group? We administered social-choice tasks to more than 1,000 children and adults differentially affected by wars in the Republic of Georgia and Sierra Leone. We found that greater exposure to war created a lasting increase in people's egalitarian motivations toward their in-group, but not their out-groups, during a developmental window starting in middle childhood (around 7 years of age) and ending in early adulthood (around 20 years of age). Outside this window, war had no measurable impact on social motivations in young children and had only muted effects on the motivations of older adults. These "war effects" are broadly consistent with predictions from evolutionary approaches that emphasize the importance of group cooperation in defending against external threats, though they also highlight key areas in need of greater theoretical development.

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An important question to microfinance is the relevance of existing social capital in target communities to the performance of group lending. This research presents evidence from field experiments in South Africa and Armenia, in which subjects participate in trust and microfinance games. We present evidence that personal trust between group members and social homogeneity are more important to group loan repayment than general societal trust or acquaintanceship between members. We also find some evidence of reciprocity: those who have been helped by other group members in the past are more likely to contribute in the future. Copyright 2007 The Author(s). Journal compilation Royal Economic Society 2007.

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Recent advances have highlighted the evolutionary significance of female competition, with the sexes pursuing different competitive strategies and women reserving their most intense competitive behaviors for the benefit of offspring. Influential economic experiments using cash incentives, however, have found evidence suggesting that women have a lower desire to compete than men. We hypothesize that the estimated gender differences critically depend on how we elicit them, especially on the incentives used. We test this hypothesis through an experiment with adults in China (n = 358). Data show that, once the incentives are switched from monetary to child-benefitting, gender differences disappear. This result suggests that female competition can be just as intense as male competition given the right goals, indicating important implications for policies designed to promote gender equality.ollowing pioneering works by Hrdy and Clutton-Brock, significant advances in evolutionary biology, psychology, and anthropology have produced an important body of knowledge on the occurrence and evolutionary significance of female competition (1-5). Despite Darwin's recognition of the importance of intrasexual competition, male-male and female-female competition for resources and sexual reproduction (6), most subsequent work has focused on the mechanisms and consequences of male competition. From an evolutionary perspective, variance in female reproductive outcomes [especially given the successful spread of monogamous marriage norms which reduces sex differences in the opportunity for sexual selection (4, 5, 7)] implies that men and women have been subject to similarly intense selection pressures (1,8). If competitive traits derive from selection pressures, then men and women should each have evolved competitive traits. Recently, important studies have laid the foundation for understanding the difference in competitive strategies pursued by the sexes and, in particular, found that females reserve their most intense competitive behaviors for the benefit of offspring (3,5,8). The goal of this paper is to contribute new behavioral evidence to the study of the different modalities of women's competition.Economists have long observed that sex differences in behavior exist and have consistently documented a gender gap in the desire to compete (9-13). In the standard experimental design on selection into competitive environments, men and women are given a series of computational tasks under different payment conditions and then asked to choose the preferred payment method for a subsequent task (9). Despite the lack of a gender difference in performance, when offered the choice to be paid on a tournament payment scheme or a noncompetitive piece-rate payment scheme, men usually choose tournament significantly more often than women. Controlling for confidence and risk aversion does not explain away the gender gap in choosing tournament. Numerous subsequent studies have replicated this finding, in the laboratory and in the field, and have exp...

The "Virtual Paper" section provides hyperlinks to already published papers in other journals, which are selected by the editors as excellent papers in topological science and technology.