Handling of smaller infants by individuals other than the mothers was studied for wild chimpanzees. Nulliparous subadult females, who are related or unrelated to the infants, are most earnest caretakers, while parous females usually are indifferent to infants other than their own. Adult males also take care of infants, although more briefly than nulliparae. Mothers screen alloparental candidates by sex and kin relationship. ‘Learn-to-mother’ hypothesis is supported for alloparental behavior by nulliparae. Costs and benefits of alloparental behavior by various age/sex classes are discus