Visual Discrimination of Kin in Mandrills

Phenotype matching, a learning mechanism that evolved based on phenotypic cues shared among relatives, may provide animals with the ability to recognize unfamiliar kin. The generalization of this mechanism across animal species is debated, however, because appropriate tests are difficult to design due to possible confounding effects of familiarity. Hence, only a few studies have examined evidence for the existence of such a mechanism in natural populations. Here, we tested the phenotype matching hypothesis based on visual cues in a semi‐free‐ranging population of mandrills (Mandrillus sphinx) that contains individuals related to different degrees and where familiarity is controlled for. Using an experimental design based on the presentation of photographs, we show that mandrills discriminate unfamiliar relatives using facial cues alone. Our results build on earlier studies, showing that primates use phenotype matching to recognize and subsequently discriminate unfamiliar kin. We suggest that facial features along with other visual and non‐visual cues provide a proximate mechanism for kin selection to operate.