Neonatal face-to-face interactions promote later social behaviour in infant rhesus monkeys.

In primates, including humans, mothers engage in face-to-face interactions with their infants, with frequencies varying both within and across species. However, the impact of this variation in face-to-face interactions on infant social development is unclear. Here we report that infant monkeys (Macaca mulatta) who engaged in more neonatal face-to-face interactions with mothers have increased social interactions at 2 and 5 months. In a controlled experiment, we show that this effect is not due to physical contact alone: monkeys randomly assigned to receive additional neonatal face-to-face interactions (mutual gaze and intermittent lip-smacking) with human caregivers display increased social interest at 2 months, compared with monkeys who received only additional handling. These studies suggest that face-to-face interactions from birth promote young primate social interest and competency.

Neonatal imitation and early social experience predict gaze following abilities in infant monkeys.

Individuals vary in their social skills and motivation, the causes of which remain largely unknown. Here we investigated whether an individual's propensity to interact with others measured within days after birth, and differences in infants' early social environment, may predict a later social skill. Specifically, we tested whether neonatal imitation--newborns' capacity to match modelled actions--and social experience in the first months of life predict gaze following (directing attention to locations where others look), in infant macaques (Macaca mulatta; n = 119). Facial gesture imitation in the first week of life predicted gaze following at 7 months of age. Imitators were better at gaze following than non-imitators, suggesting neonatal imitation may be an early marker predicting socio-cognitive functioning. In addition, infants with rich social environments outperformed infants with less socialization, suggesting early social experiences also support the development of infants' gaze following competence. The present study offers compelling evidence that an individual difference present from birth predicts a functional social cognitive skill in later infancy. In addition, this foundational skill--gaze following--is plastic, and can be improved through social interactions, providing infants with a strong foundation for later social interaction and learning.