A Cross-Cultural Analysis of Brazilian, Russian, and American Families

Inclusive fitness theory postulates that preferentially provisioning offspring that most closely resemble the parents can indirectly increase their gene-copying success, with phenotypic resemblance between (allo)parent and offspring acting as an indicator of genetic similarity. According to this prediction, the amount of alloparental effort should correlate with parent-offspring resemblance cues, and this effect should be more pronounced for fathers and paternal kin, as paternity certainty is concerned predominantly with men. We tested these predictions and conducted an online survey in 2019 in Brazil (N = 605), Russia (N = 302), and the USA (N = 308). By examining the relationship between parent-child resemblance and kin altruism, we have uncovered a widespread positive correlation between parent-child resemblance and the willingness of parents and grandparents to provide care. For example, the more a child resembles their father, the more parents and grandparents are likely to provide support. Similarly, the resemblance between a mother and child is positively associated with (allo)parental effort. At the same time, greater similarity between father and child can actually discourage matrilineal grandparents fr om providing childcare. In this respect, our data challenge the conventional viewpoint that paternity uncertainty and father-child similarity cues are the driving force behind paternal kin investments, but not maternal ones. Our results suggest that a more general kin recognition mechanism is at play, one that is shared by both matrilineal and patrilineal relatives in modern societies. One possible explanation is that in the context of the extended family, mothers and maternal relatives, as primary caregivers, may be particularly sensitive to key phenotypic traits of dependent children. In the resulting model a sufficient cross-cultural difference emerges when examining the degree of assistance provided by different (allo)parents across the studied samples. For instance, American respondents highlighted a significant level of paternal involvement in childcare, while Russian respondents noted a high level of maternal kin assistance. In contrast, the Brazilian sample exhibited relatively low levels of kin involvement. The divergent paths of these countries raise important questions about the future of family structures and the role of kinship in shaping them. The highly urbanized Brazilian sample may provide valuable insights into possible future directions in family structure and the role of alloparental care within it. We propose that Brazil's high social integration and family member's incorporation into expanded social networks may contribute to the development of a communal model of breeding, marked by ultra-social or eusocial childcare practices. Will the Russian and American models of family follow the same ultra-social path as the Brazilian one? Or will Russian and US families maintain a distinct approach to childcare in a world influenced by globalization? We suppose that further field work on alloparental care in the Latin American region is essential to shed light on this important topic, and to uncover the answers to these intriguing questions.