Touching faces: The active role of infant capuchin monkeys (Sapajus libidinosus) in their social development.

Touch has a significant impact on the development of infant primates, but it is still understudied. Little is reported, for example, about the effect of infants' touch on their environment and social development. In this study, we sought to fill this gap by investigating the touch of capuchin monkey (Sapajus libidinosus) infants on the faces of other individuals in the group. We followed eight wild infants (four females and four males) across their first 3 years of life and assessed whether this behavior is part of the social repertoire and whether it facilitates facial recognition. We coded all social events of the infants in 127.3 hr of video recorded weekly from birth until 36 months, through daily focal sampling. We recorded motor patterns of the behavior, the context, the partner touched, and the partners' response to each infant face touching. We found that touching was always associated with affiliative contexts. Infant face touching of other group members was associated with lipsmacking and grooming, consistently involving visual contact and exploration of the face by the infant's hand. In this species, face touching also occurred in response to engagement initiated by the touched individual, potentially signaling reciprocity in affiliative interactions and serving as a pleasurable gesture. (PsycInfo Database Record (c) 2025 APA, all rights reserved).