This chapter examines causal processes underlying change in demographic outcomes among the Tsimane of lowland Bolivia. Prospective data collected between 2002 and 2010 shows that the loss of an infant leads to an earlier progression to the next birth, as do prospective measures of maternal health. The total fertility rate is about 8.8, but greater integration with the Bolivian market and educational system is associated with lower fertility rates. The data indicate tangible trade-offs between fertility and infant mortality. Infants of first-time mothers who delay reproduction show significantly improved survival rates. Short interbirth intervals increase the mortality risks of subsequent infants. Indicators of the mother's nutritional and health status also significantly predict infant mortality. These results reflect the bidirectionality of relationships between fertility and mortality that evolutionary biologists and recently demographers have noted: sustained increases as well as decreases in fertility may be characteristic of early stages of demographic transition.
Kaplan, H., Hooper, P. L., Stieglitz, J., & Gurven, M. (2015). The Causal Relationship between Fertility and Infant Mortality: Prospective analyses of a population in transition. In Population in the Human Sciences: Concepts, Models, Evidence. Oxford University Press. https://doi.org/10.1093/acprof:oso/9780199688203.003.0013