From the womb to the tomb: The role of transfers in shaping the evolved human life history

Abstract

Humans are the longest living and slowest growing of all primates. Although most primates are social, humans are highly cooperative and social in ways that likely co-evolved with the slow human life history. In this paper we highlight the role of resource transfers and non-material assistance within and across generations in shaping low human mortality rates. The use of complex cooperative strategies to minimize risk is a necessary precursor for selecting further reductions in mortality rate in late adulthood. In conjunction with changes in the age-profile of production, the impacts of resource transfers and other forms of cooperation on reducing mortality likely played an important role in selection on post-reproductive lifespan throughout human evolution. Using medical data and ethnographic interviews, we explore several types of common risks experienced by Tsimane forager-horticulturalists, and quantify the types and targets of aid. Our results illustrate the importance of transfers in several key domains and suggest that the absence of transfers would greatly increase human mortality rates throughout the life course.

Men’s status and reproductive success in 33 nonindustrial societies: Effects of subsistence, marriage system, and reproductive strategy

“…Status may increasingly serve an insurance function as men age, enabling preferential access to resources during periods of famine, illness, or conflict (62). In various nonindustrial societies, status is synonymous with number of allies (13), who are sources of aid during conflict (63), illness (33,64), and resource shortage (12,65). Even if these social connections do not lower offspring mortality, they can be instrumental to adult offspring's own status acquisition (66).…”

“…The particular traits that underlie dominance and prestige may vary across groups, but dominance and prestige are often based on conspicuous, interindividual differences in body size (6); intelligence and skill (7); consumption (8); and generosity (9,10). Relative to the status hierarchies of other primates, prestige contributes heavily to human status, because of our interdependence in production and reproduction (11,12), and thus the value of social partners and mates who are strong, skilled, wealthy, or generous (3,13). Furthermore, humans frequently cooperate against dominant individuals who act coercively (14,15).…”

Human mortality improvement in evolutionary context

“…At this age, selection pressure is highest and should have pushed mortality at maturity to its lowest possible level. When transfers of resources between kin are an important factor, as in humans (33), the force of selection against individuals at the onset of reproduction should be particularly strong (34,35). However, the lowest mortality level achieved by evolution, as revealed by the experience of huntergatherers, was magnitudes above the >200-fold lower levels recently achieved in Japan, Sweden, and other postindustrial societies.…”

Skills, division of labour and economies of scale among Amazonian hunters and South Indian honey collectors

“…It may be that Tsimane' prefer to hunt solitarily most of the time owing to difficulties in coordinating departures with other hunters, risks of free-riding or other transaction costs [2,10,37,44]. Hunting independently may also allow sharing partners to reduce variability in the production of meat; given that the Tsimane' mix hunting with horticulture and fishing, sending out hunters on alternate days could help smooth consumption within sharing clusters through time [3,12,20,45]. Distinguishing between these possibilities will require additional research that avoids the problems of self-selection inherent in observational data.…”