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.

Although cooperative social networks are considered key to human evolution, emphasis has usually been placed on the functions of men’s cooperative networks. What do women’s networks look like? Do they differ from men’s networks and what does this suggest about evolutionarily inherited gender differences in reproductive and social strategies? In this paper, we test the ‘universal gender differences’ hypothesis positing gender-specific network structures against the ‘gender reversal’ hypothesis that posits that women’s networks look more ‘masculine’ under matriliny. Specifically, we ask whether men’s friendship networks are always larger than women’s networks and we investigate measures of centrality by gender and descent system. To do so, we use tools from social network analysis and data on men’s and women’s friendship ties in matrilineal and patrilineal Mosuo communities. In tentative support of the gender reversal hypothesis, we find that women’s friendship networks in matriliny are relatively large. Measures of centrality and generalized linear models otherwise reveal greater differences between communities than between men and women. The data and analyses we present are primarily descriptive given limitations of sample size and sampling strategy. Nonetheless, our results provide support for the flexible application of social relationships across genders and clearly challenge the predominant narrative of universal gender differences across space and time.

Long-lasting, romantic partnerships are a universal feature of human societies; but almost as ubiquitous is the risk of instability when one partner strays. Jealous response to the threat of infidelity is well-studied, but most empirical work on the topic has focused on a proposed sex difference in the type of jealousy (sexual or emotional) men and women find most upsetting, rather than on how jealous response varies 1,2. This stems in part from the predominance of studies using student samples from industrialized populations, which represent a relatively homogenous group in terms of age, life history stage, and social norms 3,4. To better understand variation in jealous response, we conducted a two-part study in 11 populations (1,048 individuals). In line with previous work, we find a robust sex difference in the classic forced-choice jealousy task. However, we also show substantial variation in jealous response across populations. Using parental investment theory, we derived several predictions about what might trigger such variation. We find that greater paternal investment and lower frequency of extramarital sex are associated with more severe jealous response. Partner jealousy thus appears to be a facultative response, reflective of the variable risks and costs of men's investment across societies. Main One of the essential features of human mating is the prominence of stable, long-lasting partnerships, which in almost every society are socially enforced through the institution of marriage 5,6. A widespread feature of marriage is the custom of sexual exclusivity. Despite the near ubiquity of this expectation, marriages are at risk of disruption by extramarital partnerships. Adultery is the most commonly cited reason for divorce across cultures 7 , and concurrent partnerships are often common 8,9. In response to threats of infidelity, humans, like other species with stable partnerships, have evolved adaptations to protect against mate poaching and defection. Some of these behaviors, like partner concealment, vigilance and sexual coercion, are shared with other species 10-12 , while others like foot binding and purdah are culturally constructed and unique to humans 13,14. Underlying these behaviors is a suite of psychological mechanisms, of which jealousy is one of the most important. While jealousy itself is thought to be a universal human emotion, traditional evolutionary explanations predict that jealous response to cues of infidelity will differ in men and women, reflecting the unique adaptive problems they face 1,13,14. Men face a risk of paternity uncertainty, which results in the loss of a fitness opportunity, but also in the potential misallocation of investment. Women, on the other hand, risk the diversion of critical resources by their partner

Although cooperative social networks are considered key to human evolution, emphasis has usually been placed on the functions of men’s cooperative networks. What do women's networks look like? Do they resemble or differ from men's and what does this suggest about evolutionarily inherited gender differences in reproductive and social strategies? In this paper, we test the ‘universal gender differences’ hypothesis positing gender-specific network structures against the ‘gender reversal’ hypothesis that posits women's networks looking more 'masculine' under matriliny. Specifically, we ask whether men's friendship networks are always larger than women's and we investigate measures of centrality by gender and descent system. To do so, we use tools from social network analysis and data on men’s and women’s friendship ties in matrilineal and patrilineal Mosuo communities. In tentative support of the gender reversal hypothesis, we find that women's friendship networks in matriliny are relatively large. Measures of centrality and generalized linear models otherwise reveal greater differences between communities than between men and women. The data and analyses we present are primarily descriptive given limitations of sample size and sampling strategy. Nonetheless, our results provide support for the flexible application of social relationships across genders and clearly challenge the predominant narrative of universal gender differences across space and time.