Although cooperative social networks are considered key to human evolution, emphasis has most often been placed on the functions of male cooperative networks. As a result, gender differences in social networks are under-studied and remain incompletely theorized. Variation in kinship systems may be leveraged to test and generate hypotheses that explain the causes and effects of variation in gendered social networks. Specifically, by linking socio-ecological drivers to variation in kinship systems, human behavioral ecology provides a framework to anticipate and explain divergent patterns in gendered social networks within different kinship ecologies. In this paper, we test the ‘universal gender differences’ hypothesis positing gender-specific network structures against the ‘gender reversal’ hypothesis that women’s social networks in matriliny will more closely resemble those of men’s in patriliny. We compare these hypotheses using tools from social network analyses and data on men’s and women’s social networks in matrilineal and patrilineal Mosuo communities. In support of the gender reversal hypothesis, we find that women’s networks in matriliny are more similar to men’s in patriliny. Specifically, women in matriliny have higher edge density than do men, and women have higher measures of degree centralization than do men in matriliny whereas patrilineal men have higher measures of centrality than do women. Additionally, we find that geographic proximity and relatedness together predict women’s friendships in patriliny whereas relatedness predominates in matriliny. Finally, we find that friendship predicts ties in other domains of cooperation and social support. These results support the idea that the socio-ecological factors that result in different kinship systems also impact the ways that men and women operate within these systems, underscoring the importance of human flexibility in family making, and challenging the predominant narrative of universal gender differences.