Development of adiposity among Ju/'Hoansi Hunter-Gatherers.

OBJECTIVES: To characterize the development of childhood adiposity among the Ju'/Hoansi, a well-known hunter-gather group, to compare our results to U.S. references and to recently published results from Savanna Pume' foragers of Venezuela, with the goal of expanding our understanding of adipose development among human hunter-gatherers. METHODS: Triceps, subscapular, and abdominal skinfolds, along with height and weight from ~120 Ju'/Hoansi girls and ~103 boys, ages 0 to 24 years, collected in 1967-1969 were analyzed using best-fit polynomial models and penalized spines to characterize age-specific patterns of adiposity and their relationship to changes in height and weight. RESULTS: Overall, Ju/'Hoansi boys and girls exhibit small skinfolds with a decline in adiposity from 3 to 10 years, with no consistent differences among the three skinfolds. Increases in adiposity during adolescence precede peak height and weight velocities. Adiposity declines during young adulthood for girls and remains largely constant for boys. DISCUSSION: Compared to U.S. standards, the Ju/'Hoansi show a strikingly different pattern of adipose development, including the lack of an adiposity rebound at the onset of middle childhood, and clear increases in adiposity only at adolescence. These findings are consistent with published results from the Savanna Pumé hunter-gatherers of Venezuela, a group with a very different selective history, suggesting that the adiposity rebound does not characterize hunter-gathering populations more generally. Similar analyses in other subsistence populations are called for to confirm our results, and help distinguish the impact of specific environmental and dietary factors on adipose development.

Effects of family planning on fertility behaviour across the demographic transition.

The adoption of contraception often coincides with market integration and has transformative effects on fertility behavior. Yet many parents in small-scale societies make decisions about whether and when to adopt family planning in an environment where the payoffs to  have smaller families are uncertain. Here we track the fertility of Maya women across 90 years, spanning the transition from natural to contracepting fertility. We first situate the uncertainty in which fertility decisions are made and model how childbearing behaviors respond. We find that contraception, a key factor in cultural transmission models of fertility decline, initially has little effect on family size as women appear to hedge their bets and adopt fertility control only at the end of their reproductive careers. Family planning is, however, associated with the spread of lower fertility in later cohorts. Distinguishing influences on the origin versus spread of a behaviour provides valuable insight into causal factors shaping individual and normative changes in fertility.