Matjes River Rock Shelter is a large shell midden on the southern coast of South 
Africa. Stable nitrogen (delta(15)N) and carbon (delta(13)C) 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(15)N results show a progressive increase in individuals from birth to 1.5 
years old. delta(13)C results are more tightly clustered and mirror the steady 
progressive change seen for delta(15)N. 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 breastfeeding, and thus long interbirth intervals, among 
prehistoric foragers, even when those foragers lived in an environment with 
abundant food resources.