Aspects of cognitive immaturity may serve both to adapt children to their immediate environment and to prepare them for future ones. Language may have evolved in children's groups in the context of play. Developmental plasticity provides variability upon which natural selection operates, and such plasticity, that likely played an important role in the evolution of language, characterizes human children today.

Fincher & Thornhill (F&T) present a model of in-group assortative sociality resulting from differing levels of parasite-stress in differing geographical locations in the United States and the world. Their model, while compelling, overlooks some important issues, such as mutualistic associations with parasites that are beneficial to humans and how some religious practices increase parasite risk.