Adoptions of unrelated infants in wild Taihangshan macaques (), Jiyuan, north China.

Infant-care behavior, a range of caring behaviors by parental or alloparental individuals towards infants unable to live independently, plays a significant role in the survival of infants and the continuation of the species in non-human primates. During a behavioral ecological study of Taihangshan macaques, we observed 2 cases of infant adoptions by unrelated adult females. In case 1, a multiparous female adopted a lost infant from a neighboring group, with the infant being snatched back by her biological mother 35 days after the adoption. This is the first report of cross-group adoption in . In case 2, a nulliparous adult female, who had been once adopted by her elder sister, adopted an orphan from her group for 36 days. We describe the details of adoptions in Taihangshan macaques and explore possible reasons for adoptions to contribute to understanding the evolution of infant-care behavior and altruistic behavior of adoption in primates.