Humans are an exceptionally cooperative species, but there is substantial variation in the extent of cooperation across societies. Understanding the sources of this variability may provide insights about the forces that sustain cooperation. We examined the ontogeny of prosocial behavior by studying 326 children 3-14 y of age and 120 adults from six societies (age distributions varied across societies). These six societies span a wide range of extant human variation in culture, geography, and subsistence strategies, including foragers, herders, horticulturalists, and urban dwellers across the Americas, Oceania, and Africa. When delivering benefits to others was personally costly, rates of prosocial behavior dropped across all six societies as children approached middle childhood and then rates of prosociality diverged as children tracked toward the behavior of adults in their own societies. When prosocial acts did not require personal sacrifice, prosocial responses increased steadily as children matured with little variation in behavior across societies. Our results are consistent with theories emphasizing the importance of acquired cultural norms in shaping costly forms of cooperation and creating cross-cultural diversity.development | population differences | gene-culture coevolution

Intent and mitigating circumstances play a central role in moral and legal assessments in large-scale industrialized societies. Although these features of moral assessment are widely assumed to be universal, to date, they have only been studied in a narrow range of societies. We show that there is substantial cross-cultural variation among eight traditional small-scale societies (ranging from hunter-gatherer to pastoralist to horticulturalist) and two Western societies (one urban, one rural) in the extent to which intent and mitigating circumstances influence moral judgments. Although participants in all societies took such factors into account to some degree, they did so to very different extents, varying in both the types of considerations taken into account and the types of violations to which such considerations were applied. The particular patterns of assessment characteristic of large-scale industrialized societies may thus reflect relatively recently culturally evolved norms rather than inherent features of human moral judgment. morality | intentions | cognition | culture | human universals

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour.

Laughter is a nonverbal vocal expression that often communicates positive affect and cooperative intent in humans. Temporally coincident laughter occurring within groups is a potentially rich cue of affiliation to overhearers. We examined listeners’ judgments of affiliation based on brief, decontextualized instances of colaughter between either established friends or recently acquainted strangers. In a sample of 966 participants from 24 societies, people reliably distinguished friends from strangers with an accuracy of 53–67%. Acoustic analyses of the individual laughter segments revealed that, across cultures, listeners’ judgments were consistently predicted by voicing dynamics, suggesting perceptual sensitivity to emotionally triggered spontaneous production. Colaughter affords rapid and accurate appraisals of affiliation that transcend cultural and linguistic boundaries, and may constitute a universal means of signaling cooperative relationships.

Seeking out extra-pair paternity (EPP) is a viable reproductive strategy for females in many pairbonded species. Across human societies, women commonly engage in extra-marital affairs, suggesting this strategy may also be an important part of women's reproductive decision-making. Here, I show that among the Himba 17 per cent of all recorded marital births are attributed by women to EPP, and EPP is associated with significant increases in women's reproductive success. In contrast, there are no cases of EPP among children born into 'love match' marriages. This rate of EPP is higher than has been recorded in any other small-scale society. These results illustrate the importance of seeking EPP as a mechanism of female choice in humans, while simultaneously showing it to be highly variable and context-dependent.

The division of labor has typically been portrayed as a complementary strategy in which men and women work on separate tasks to achieve a common goal of provisioning the family. In this paper, we propose that task specialization between female kin might also play an important role in women's social and economic strategies. We use historic group composition data from a population of Western Desert Martu Aborigines to show how women maintained access to same-sex kin over the lifespan. Our results show that adult women had more same-sex kin and more closely related kin present than adult men, and they retained these links after marriage. Maternal co-residence was more prevalent for married women than for married men, and there is evidence that mothers may be strategizing to live with daughters at critical intervals-early in their reproductive careers and when they do not have other close female kin in the group. The maintenance of female kin networks across the lifespan allows for the possibility of cooperative breeding as well as an all-female division of labor.

The matrilineal Mosuo of Southwest China have been described as the only human society that lacks fathers and husbands. These claims are based on ethnographic descriptions of normative practices and have typically not employed rigorous tests of quantitative behavioral or demographic data to verify actual practices. Here we challenge these claims, providing quantitative evidence of paternal investment among contemporary Mosuo fathers.We show that co-residence with one's biological father is associated with increased education and lower age at first reproduction, suggesting that incentives to provide paternal care exist among the Mosuo. We examine men's selfreports of fathering activity and women's reports of their partners' fathering activities, including measures of both direct care and monetary investment in their children. Every participant (N = 140) reported paternal involvement in childcare, but factor analysis of fathers' responses revealed that men specialized in either monetary or direct care. We speculate as to what may lie behind differences in caring patterns and conclude by emphasizing that while paternal investment is facultative, it is unlikely to be completely absent even in societies like the Mosuo. [human behavioral ecology, paternal investment, fathers, tourism, matriliny] American /academics/asianstudies/meet-our-faculty/Pages/Tami-Blumenfield.aspx NOTES Acknowledgments. The authors would like to thank their Mosuo participants for humor, candor, and companionship during the many months of combined fieldwork that allowed us to explore the roles of fathers in their daily lives. We are indebted to Michael Chibnik, Mayumi Shimose, and the anonymous reviewers who provided useful comments and criticisms on earlier drafts of this article. the invaluable scholarly perspectives and practical assistance from He Shaoying, He Zhonghua, Lamu Gatusa, and Latami Dashi. We thank Jiajia Wu and Hsun-Hui Tseng for assistance in translating the abstract to Chinese.

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