Nonmaternal care: a half-century of research.

This paper aims to serve three purposes, providing: 1. a half-century retrospective on research in on nonmaternal care of the young, with an emphasis on key advances; 2. a commentary on the research papers in this special issue on nonmaternal care; and 3. a summary of nonmaternal care among hunting-and-gathering cultures-representing the human Environments of Evolutionary Adaptedness (EEAs)-in the broader context of human evolution. While the research being done now is excellent and uses appropriate evolutionary theory and cutting-edge methods ranging across behavioral biology (field and laboratory observational studies, controlled experiments, careful behavioral measures, energetics, neurotransmitter function, neuroendocrinology, neuroimaging, and genetics, among others), it is difficult to make generalizations beyond stating that nonmaternal care is a multifaceted evolved function in some species, which usually contributes to the reproductive success of the mother and the survival of the young. Why it evolved when and where it did is not an impenetrable question, but needs further research. The same is true for the mechanistic biology of various types of allomaternal care. I conclude with some observations on historical changes in non-maternal care since the hunting-gathering era, including in industrial and postindustrial cultures. It is evident that in the human species at least, many arrangements for care of the young are possible and adaptive.