Current issues in sibling detection

Sibling Relations in Patchwork Families: Co-residence Is More Influential Than Genetic Relatedness

In "patchwork" families, full siblings, maternal and paternal half-siblings, and non-related children are raised together, and sometimes, genetically related children are separated. As their number is steadily growing, the investigation of the factors that influence within-family relations is becoming more important. Our aim was to explore whether people differentiate between half- and full-siblings in their social relations as implied by the theory of inclusive fitness, and to test whether co-residence or genetic relatedness improves sibling relations to a larger extent. We administered the Sibling Relationship Questionnaire to 196 individuals who were in contact with full-, half-, or step-siblings in their childhood. We built Generalized Linear Mixed Models models to test for the effects of relatedness and co-residence on sibling relations. In general, a higher degree of relatedness was associated with better sibling relations, but only among those who did not live together during childhood. Co-resident siblings' overall pattern of relation quality was not influenced by the actual level of genetic relatedness. In contrast to this, full siblings reported having experienced more conflicts during childhood than half-siblings, possibly resulting from enhanced competition for the same parental resources. The results suggest that inclusive fitness drives siblings' relations even in recent industrial societies. However, among individuals who live together, the effect of relatedness might be obscured by fitness interdependence and the subjective feeling of kinship.

What evidence is required to determine whether infants infer the kinship of third parties? A commentary on Spokes and Spelke (2017)

Research into the cognitive capacities of infants has revealed a rich assortment of competencies that help to structure inferences across multiple content domains. Despite these advances, researchers have paid relatively little attention to a domain crucial to social life: kinship. One recent exception is a set of studies by Spokes and Spelke (2017), who report evidence that 15 to 18-month-old infants expect social affiliation between two babies receiving care from the same adult. The experiments reported by Spokes and Spelke raise the key question of whether infants harbor intuitions regarding kinship-and provide tantalizing hints that they do. But determining whether the infant inferences found in these experiments in fact do implicate a kin-specific psychology is not straightforward, as kinship and social group membership overlap. Researchers need a set of criteria for ascertaining whether individuals (preverbal infants in particular but also children and adults alike) infer kinship-the likely genetic relatedness-between agents based on interactions with a common 3rd party and then use this information to guide expectations of behavior. Here, we consider the nature of evidence that would be needed to establish in principle that infants make inferences specific to kinship. In doing so, we link the developmental literature on infant social cognition to adult kin detection research, which has previously grappled with the question of what evidentiary standards reasonably establish the presence of kin-specific inferences. In light of prior empirical and theoretical work, we advance four criteria for establishing the presence of tacit knowledge of kinship, assess the extent to which the studies presented by S&S meet these criteria, and use the criteria to inform and spark directions for future research.