The sibling uncertainty hypothesis: Facial resemblance as a sibling recognition cue

For the same reason that fathers could not have been certain their mates’ offspring were their genetic progeny during human evolutionary history, full siblings could not have been certain that they shared paternal genes. Previous kin recognition research suggests facial resemblance is a cue men use to help solve the adaptive problem of paternity uncertainty and identify their biological offspring. Facial resemblance may also be a cue individuals use to identify siblings who share paternal genes. In the current study, facial resemblance between siblings was hypothesized to be positively associated with their emotional closeness and altruism, and inversely related with their frequency of conflict. Within families, individuals reported greater closeness and altruism toward siblings who more closely resembled them. In contrast with previous offspring recognition research, the effects of resemblance were not sex-differentiated, suggesting that facial resemblance is a cue both sexes use in sibling recognition.