Relationship between subsistence and age at weaning in "preindustrial" societies

Cross-cultural studies have revealed broad quantitative associations betwee n subsistence practice and demographic parameters for preindustrial populat ions. One explanation is that variation in the availability of suitable wea ning foods influenced the frequency and duration of breastfeeding and thus the length of interbirth intervals and the probability of child survival (t he "weaning food availability" hypothesis). We examine the available data o n weaning age variation in preindustrial populations and report results of a cross-cultural test of the predictions that weaning occurred earlier in a gricultural and pastoral populations because dairy and cereal production in creased the availability of easily digestible, nutrient-rich foods appropri ate for weaning. We found that, contrary to predictions, supplementation wi th liquid foods other than breast milk was delayed in agricultural populati ons relative to less agriculturally dependent ones and complementary feedin g with solid foods was delayed in pastoral populations relative to those le ss dependent on herding. Although the duration of breastfeeding was longer in populations dependent on hunting, there was no qualitative evidence that such populations lacked foods appropriate for weaning. The patterns observ ed suggest that the relationships between demography and subsistence observ ed among preindustrial societies cannot be explained by the "weaning food a vailability" hypothesis. We discuss the implications for understanding the mechanisms underlying prehistoric human demography, subsistence shifts, all ocation to parenting and mating effort, and the evolutionary implications o f tradeoffs between diet and disease.