Development of kin bias among rhesus monkeys: Maternal transmission or individual learning?

We examined the possible roles of maternal transmission and independent learning in the development and perpetuation of kin networks across generations of free-ranging rhesus monkeys, Macaca mulatta, on Cayo Santiago, Puerto Rico. We tested predictions derived from maternal transmission and independent learning hypotheses by examining the extent to which variation in the degree of kin bias displayed by individual infants was related to variation in mother-infant interaction and aspects of the infant's social environment. High levels of kin bias in infants were related independently to high levels of both proximity to the mother and to potential risk. At 25-30 weeks of age, infants displayed degrees of kin bias that were moderately correlated with those of their mothers. However, infants that spent large amounts of time near the mother did not necessarily develop degrees of kin bias that were highly similar to those of their mothers. The extent to which infants developed degrees of kin bias similar to their mothers was significantly correlated with the degree to which they experienced similar levels of social risk. The results suggest that, while intense mother-infant interaction contributes to the development of high degrees of kin bias in infants, the perpetuation of similar degrees of kin bias across generations may depend on mothers and infants having similar experiences with mutual kin and nonkin. We suggest that the perpetuation of kin bias across generations may be viewed as socially biased independent learning.