Growing into adulthood – a review on sex differences in the development of sociality across macaques

Preferential affiliative relationships, or social bonds, play a crucial role in primate social life, but little is known about their development. Here, we review macaque studies investigating the social development of both sexes. Firstly, we highlight the emergence of sex differences in mother–offspring bonds, as macaque mothers form stronger bonds with daughters, while being more aggressive towards sons, possibly contributing to maintain female philopatry and/or male dispersal. Secondly, despite paternity uncertainty, we discuss studies reporting that fathers of several macaque species preferentially engage with their offspring, but less than mothers and only in periods of high infant mortality. Thirdly, we show that immature females, the philopatric sex in macaques, already form stronger bonds with close maternal kin than immature males, mirroring social patterns during adulthood. However, this bias seems not caused by kin availability, as kin availability is similar for both sexes prior to male dispersal. Moreover, immature males might preferentially affiliate with paternal kin over non-kin, possibly because of lower maternal integration in their maternal family and/or in preparation of dispersal. Fourthly, we discuss how immature females engage in grooming and proximity with female partners as they grow older, while immature males preferentially interact with adult males and peers, playing more than females from early on. Finally, we show that most developmental changes in sociality happen around 2–3 years of age, probably representing a milestone in macaque social development. We conclude that sex differences in sociality emerge early in development and increase through time, with sexes gradually growing into their adult roles