Throughout the animal kingdom, related conspecifics show similar features. Some are the spitting image of each other. However, whether resemblance between kin merely reflects their genetic resemblance or results from selection to facilitate their recognition is still unknown. A team of scientists led by Marie Charpentier of the ISEM in Montpellier, including Clémence Poirotte and Peter Kappeler of the German Primate Center in Göttingen, used for the first time artificial intelligence (deep learning) to examine the hypothesis that the similarity of the facial features of free-living mandrills is the result of selection. The database consisted of 16,000 portraits of mandrills, taken since 2012 as part of the Project Mandrillus in Gabon. This natural population of mandrills is the only one habituated to the presence of humans. Using a trained algorithm of deep learning, the individuals were first identified and then quantified in terms of facial resemblance. The results were subsequently related to relatedness data of the study animals.
Mandrills live in groups consisting of more than 100 individuals and are characterized by the fact that the females are maternal relatives. They are familiar with each other and remain in the same family throughout their lives. Since reproduction in mandrill groups is mainly monopolized by the alpha male, young mandrills of similar age often have the same father. However, as members of different family groups within the large groups, they should hardly know each other. Nevertheless, half-sisters on the paternal side, as well as half-sisters on the maternal side, interact with each other more often than unrelated animals. "This observation suggests that paternal half-sisters recognize each other as relatives by their facial features. Although maternal and paternal half-sisters share the same degree of genetic relatedness, the facial resemblance is stronger among paternally related females. We suspect that the similarity of facial features between paternal relatives has evolved to facilitate social discrimination and nepotism between kin," says Clémence Poirotte.