Evolution of human lactation and complementary feeding: Implications for understanding contemporary cross-cultural variation

Abstract

Artistic reconstructions of ancestral hominids1 often depict mothers with bared breasts and suckling infants, reflecting assumptions about the importance of lactation in human evolution. However, anthropologists have published no detailed theories about how our ancestors fed young children. In the absence of a scientific model of the evolution of human lactation and complementary feeding, it is difficult to evaluate claims made about the long duration of ancient breast-feeding or the "naturalness" of lactation patterns observed in some human societies. This chapter therefore has two main goals. First, I review several lines of evidence that suggest how changes in birth spacing, foraging strategy and sociality may have increased the selective advantages of a more flexible pattern of lactation and a behavioural shift towards complementary feeding in past environments. Second, I develop a hypothesis that the complementary feeding of young children is a fundamental component of life and socio-behavioural adaptations that evolved among our human ancestors as an ecological strategy for increasing maternal fitness. I suggest that the ancestral habit of introducing safe complementary feeding after a period of exclusive breast-feeding is unique to humans. It is linked to the evolution of a species-typical care giving "package", which includes social foraging, food sharing, food processing, and a capacity to invent technological solutions to dietary challenges. I conclude with a brief review of how changes in social organisation, time allocation and diet quality that accompanied the agricultural and industrial revolutions have created an environment in which the evolved tendency to introduce foods to breast-feeding young undermines the health of populations. © 2009 Springer Netherlands.