Abstract
In humans, mothers and infants often engage in face-to-face interactions, which are often considered crucial for the social transmission of information and the typical social and cognitive development of infants. In this study, we used a comparative developmental perspective to provide an assessment of mother-infant face-to-face interactions in several great and small ape species and to better understand which aspects of face-to-face interactions are shared by humans with other species. We conducted longitudinal behavioral observations on 48 mother-infant pairs from five different genera (i.e., Hylobates: N = 9; Homo: N = 10; Nomascus: N = 6; Pan: N = 18; Symphalangus: N = 5), when infants were 1, 6, and 12 months old. Generalized linear mixed models revealed differences across ape genera and through development in the probability that mothers and infants engaged in face-to-face interactions during the first year of the offsprings' life. As predicted, these interactions were more likely when mothers and infants spent less time in physical contact, in communities usually characterized by more distal parenting styles (i.e., WEIRD humans), and when infants became older and thus motorically more independent. Overall, our findings suggest that face-to-face interactions were likely present in the common ancestor of humans and small apes, and likely serve a similar function across ape species.