Sex differences in the mother–neonate relationship in wild baboons: social, experiential and hormonal correlates

In mammals, maternal care is essential for offspring survival, yet individual differences in this care can dramatically affect offspring growth and development. Few studies have, however, investigated the sources, magnitude and consequences of naturally occurring interindividual variation in maternal care during the neonatal period. In this study, we examine several hormonal and nonhormonal predictors of naturally occurring variation in the mother–neonate relationship during the first 8 weeks of infancy in 34 wild baboon (Papio cynocephalus) mother–infant dyads in Amboseli, Kenya. We use data on physical contact and suckling patterns to assess the quality of the mother–neonate relationship and to evaluate the extent to which variation in this relationship is predictable from perinatal ovarian steroids (i.e. faecal oestrogen and progesterone metabolites), previous infant care experience, maternal dominance rank and offspring sex. We found that newborn infants of more experienced mothers initiated higher rates of changes in mother–infant contact than newborns of less experienced mothers. However, at each level of maternal experience, newborn males initiated higher rates of changes in mother–infant contact than newborn females. Moreover, we found evidence suggesting that variation in suckling activity among daughters (but not sons) was predictable from maternal dominance rank and faecal oestrogen (fE) concentrations before birth. To our knowledge, our study provides the first evidence of (1) the influence of cumulative maternal experience on the mother–infant relationship and (2) the emergence of sex differences in the mother–infant relationship during the neonatal period in wild primates. Our results suggest that the well-documented sex differences in life history, behaviour and ecology in primates (and other social mammals) may originate very early in life.