Weaning age among foragers at Matjes River Rock Shelter, South Africa, from stable nitrogen and carbon isotope analyses

Matjes River Rock Shelter is a large shell midden on the southern coast of South Africa. Stable nitrogen (delta N-15) and carbon (delta C-13) isotope ratios were measured in bone collagen and dentine from human skeletons excavated from this site in order to establish a weaning curve in mid-Holocene hunter-gatherers. delta N-15 results show a progressive increase in individuals from birth to 1.5 years old. delta C-13 results are more tightly clustered and mirror the steady progressive change seen for delta N-15. We deduce that children at Matjes River Rock Shelter were breastfed for at least the first 1.5 years after birth, and were weaned sometime between 2-4 years of age. A similar pattern was documented for historic-era Kalahari foraging people, where the interbirth spacing was approximately 3 years. This study provides the first direct evidence for an extended period of breast-feeding, and thus long interbirth intervals, among prehistoric foragers, even when those foragers lived in an environment with abundant food resources. (c) 2005 Wiley-Liss, Inc.