Maternal care is crucial for primate offspring development, particularly in species with prolonged developmental periods, such as humans and other primates. In this study, we used a cross-species and developmental approach to assess the role of mothers and infants in initiating bouts of affiliation (i.e., proximity and grooming) and visual engagement (i.e., unidirectional and mutual gaze) in humans (N = 10), great apes (N = 18) and small apes (N = 20). We observed mother-infant dyads when the offspring was 1, 6 and 12 months of age, using focal sampling. Our results showed that mothers were generally more likely than infants to initiate grooming, unidirectional and mutual gazes, but not proximity. As infants got older, mothers became even more likely to initiate unidirectional and mutual gazes, but infants also started to initiate proximity and unidirectional gazes more frequently, with infant-initiated mutual gazes peaking at around 6 months of age. Moreover, human mothers were more likely to initiate proximity than great ape mothers, and especially more than small ape mothers; in contrast, infants in great and small apes initiated proximity more frequently than human infants. These findings highlight important similarities between humans and other apes in the initiation patterns of affiliative interactions and visual engagement.
