Environmental, sex-specific, and genetic determinants of infant social behavior in a wild primate

Affiliative social bonds are linked to fitness components in many social
mammals. However, despite their importance, little is known about how the
tendency to form social bonds develops in young animals, or if the timing
of development is heritable and thus can evolve. Using four decades of
longitudinal observational data from a wild baboon population, we assessed
the environmental determinants of an important social developmental
milestone in baboons—the age at which a young animal first grooms a
conspecific—and we assessed how the rates at which offspring groom their
mothers develops during the juvenile period. We found that grooming
development differs between the sexes: female infants groom at an earlier
age and reach equal rates of grooming with their mother earlier than
males. We also found that age at first grooming for both sexes is weakly
heritable (h2 = 0.043, 95% CI: 0.002 – 0.110). These results show that sex
differences in grooming emerge at a young age; that strong, equitable
social relationships between mothers and daughters begin very early in
life; and that age at first grooming is heritable and therefore can be
shaped by natural selection.