Abstract
Adoption among nonhuman primates (hereafter primates) has been widely reported, particularly in chimpanzees, renowned for their higher intelligence and well-developed cognition. In contrast to adoption in other Old World monkeys, this case of adoption in golden snub-nosed monkeys (Rhinopithecus roxellana) involves two infants associated with three units characterized by distinct social structures and reproductive functions. Consequently, this case extends beyond traditional hypotheses on allomaternal care and adoption-such as enhancing the fitness of adoptive mothers, fostering maternal behaviors, and improving fitness through social and individual interactions-to necessitate an association with the complex social structure characterized by hierarchical, multilevel composition, akin to human society, and intense sexual selection that frequently results in infanticide. Specifically, adopting an infant with a genetic link to the dominant male of the adopting female may reduce the risk of infanticide against her offspring that do not share a biological link with the dominant male. This adoption pattern suggests that golden snub-nosed monkeys may possess more sophisticated intelligence and cognition, characteristics supported by more developed brain structure and facial muscles than the other Old World monkeys.