Reproductive trade-offs in extant hunter-gatherers suggest adaptive mechanism for the Neolithic expansion

Abstract

The Neolithic demographic transition remains a paradox, because it is associated with both higher rates of population growth 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 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.quality-quantity trade-off | epidemiological transition | hunter-gatherers | Neolithic revolution | Neolithic demographic transition

Productivity, biodiversity, and pathogens influence the global hunter-gatherer population density

“…Due to generally low population densities, it has been suggested that the prevalence of pathogens, such as influenza and measles viruses, and Plasmodium and Trypanosoma parasites is low among huntergatherers (34). In addition, it has been argued that high rates of mobility prevent the accumulation of fecal and other waste at hunter-gatherer dwelling sites, leading to a low prevalence of soil-transmitted helminths (35,36). Even if hunter-gatherers are less susceptible to pathogens than farmers who live under similar conditions of environmental pathogen stress, our findings nevertheless indicate that the interaction between pathogens and hunter-gatherers is sufficient to create a significant negative effect on hunter-gatherer abundance.…”

Signatures of recent positive selection in enhancers across 41 human tissues

“…Haplotype-based metrics such as nS L are known to be sensitive to signatures resulting from selection that occurred approximately 10,000 -20,000 years ago, which corresponds to the incidence of the Agricultural Revolution ). The advent of farming practices, communal living in settlements, and migrations of farmers across the globe resulted in an increase of numbers and densities of humans in any given location, likely facilitating the spread of pathogens (Varki and Gagneux 2009;Page et al 2016;Nielsen et al 2017). In addition, recent studies suggest that selection on cisregulatory regions, such as enhancers, might have been important in driving adaptation of modern human populations to distinct environments, due to their modular organization: change of expression pattern in one temporal or spatial context can often occur without affecting others, which could contribute to phenotypic changes without incurring negative pleiotropic effects (Carroll 2005;Wray 2007).…”

A friend in need is a friend indeed: Need-based sharing, rather than cooperative assortment, predicts experimental resource transfers among Agta hunter-gatherers

“…resources, but also in wage or agricultural labor when available. Of the time spent in economic activities, 77% concerned foraging behavior, predominantly fishing (54%), but also gathering (20%) and hunting (3%), while the remaining 23% of time was spent engaged in non-foraging behavior, such as cultivation (13.5%) and wage labor (9.5%; Page et al, 2016). Game and fish are traded with local agricultural non-Agta populations for rice, other carbohydrates and luxury goods.…”