1. Hrdy SB. 2009 Mothers and others: the evolutionary origins of mutual understanding. Cambridge, MA: Belknap Press.
2. Emmott EH, Page AE. 2019 Alloparenting. In Encyclopedia of evolutionary psychological science (eds TK Shackelford, V Weekes-Shackelford), pp. 1-14. Berlin, Germany: Springer International Publishing.
3. Lee RB, DeVore I. 1968 Man the hunter. Chicago, IL: Aldine Publishing Company.
4. The Origin of Man
5. Becker GS. 2009 A treatise on the family, enlarged edn. Cambridge, MA: Harvard University Press. See http://books.google.com/books?hl=en&lr=&id=Vnr8w6HwiAAC&pgis=1.