Parent-offspring facial resemblance increases with age in rhesus macaques

Kin recognition is a key ability which facilitates the acquisition of inclusivefitness benefits and enables optimal outbreeding. In primates, phenotypematching is considered particularly important for the recognition of patrili-neal relatives, as information on paternity is unlikely to be available viasocial familiarity. Phenotypic cues to both paternal and maternal relatednessexist in the facial features of humans and other primates. However, theoreti-cal models suggest that in systems with uncertainty parentage it may beadaptive for offspring to conceal such cues when young, in order to avoidpotential costs of being discriminated against by unrelated adults. Usingexperienced human raters, we demonstrate in a computer-based task thatdetection of parent–offspring resemblances in the faces of rhesus macaques(Macaca mulatta) increases significantly with offspring age. Moreover, thiseffect is specific to information about kinship, as raters were extremely suc-cessful at discriminating individuals even among the youngest animals.To our knowledge, this is the first evidence in non-humans for theage-dependent expression of visual cues used in kin recognition