“Reproductive Trade-Offs in Extant Hunter-Gatherers Suggest Adaptive Mechanism for the Neolithic Expansion”, 2016-04-26 (; backlinks; similar):
The rise of agriculture during the Neolithic period has paradoxically been associated with worldwide population growth despite increases in disease and mortality. We examine the effects of sedentarization and cultivation on disease load, mortality, and fertility among Agta foragers. We report increased disease and mortality rates associated with sedentarization alongside an even larger increase in fertility associated with both participation in cultivation and sedentarization. Thus, mothers who transition to agriculture have higher reproductive fitness. We provide the first empirical evidence, to our knowledge, of an adaptive mechanism behind the expansion of agriculture, explaining how we can reconcile the Neolithic increase in morbidity and mortality with the observed demographic expansion.
The Neolithic demographic transition remains a paradox, because it is associated with both higher rates of population growth [As a result, although exact estimates vary, it has been argued that average population growth rates rose from <0.001% to ~0.04% per year during the early Neolithic] and increased morbidity and mortality rates. Here we reconcile the conflicting evidence by proposing that the spread of agriculture involved a life history quality-quantity trade-off whereby mothers traded offspring survival for increased fertility, achieving greater reproductive success despite deteriorating health.
We test this hypothesis by investigating fertility, mortality, health, and overall reproductive success in Agta hunter-gatherers whose camps exhibit variable levels of sedentarization, mobility, and involvement in agricultural activities.
We conducted blood composition tests in 345 Agta and found that viral and helminthic infections as well as child mortality rates were statistically-significantly increased with sedentarization. Nonetheless, both age-controlled fertility and overall reproductive success were positively affected by sedentarization and participation in cultivation.
Thus, we provide the first empirical evidence, to our knowledge, of an adaptive mechanism in foragers that reconciles the decline in health and child survival with the observed demographic expansion during the Neolithic.
[Keywords: quality-quantity trade-off, epidemiological transition, hunter-gatherers, Neolithic Revolution, Neolithic demographic transition]