This article investigates peer relations in infancy, both in primates and in preindustrial human societies. Data from these populations shows a strong tendency toward a multi-age composition of play groups rather than solely peer-aged play groups for infants. Patterns in child care across societies of different subsistence types are empirically examined.

This chapter examines the relationship between male parental behavior and influences of species, ecological and social factors. The authors first present a cross-phylogenetic perspective on paternal differences between species, then offer two quantitative studies: a comparative study of non-western human societies that correlates father-infant proximity with socioecological factors and another about father-infant proximity among the !Kung.