Even though female food acquisition is an area of considerable interest in hunter-gatherer research, the ecological determinants of women’s economic decisions in these populations are still poorly understood. The literature on female foraging behavior indicates that there is considerable variation within and across foraging societies in the amount of time that women spend foraging and in the amount and types of food that they acquire. It is possible that this heterogeneity reflects variation in the trade-offs between time spent in food (...) acquisition and child care activities that women face in different groups of hunter-gatherers. In this paper we discuss the fitness trade-offs between food acquisition and child care that Hiwi and Ache women foragers might face. Multiple regression analyses show that in both populations the daily food acquisition of a woman’s spouse is negatively related to female foraging effort. In addition, nursing mothers spend less time foraging and acquire less food than do nonnursing women. As the number of dependents that a woman has increases, however, women also increase foraging time and the amount of food they acquire. Some interesting exceptions to these general trends are as follows: (a) differences in foraging effort between nursing and nonnursing women are less pronounced when fruits and roots are in season than in other seasons of the year; (b) foraging return rates decrease for Ache women as their numbers of dependents increase; and (c) among Ache women, the positive effect of number of dependents on foraging behavior is less pronounced when fruits are in season than at other times of the year. Lastly, in the Hiwi sample we found that postreproductive women work considerably harder than women of reproductive age in the root season but not in other seasons of the year. We discuss how ecological variation in constraints, the number of health insults to children that Hiwi and Ache mothers can avoid, and the fitness benefits they can gain from spending time in food acquisition and child care might account for differences and similarities in the foraging behaviors of subgroups of Hiwi and Ache mothers across different seasons of the year. Valid tests of the explanations we propose will require considerable effort to measure the relationship between maternal food acquisition, child care, and adverse health outcomes in offspring. (shrink)

Our objective is to test an optimality model of human fertility that specifies the behavioral requirements for fitness maximization in order (a) to determine whether current behavior does maximize fitness and, if not, (b) to use the specific nature of the behavioral deviations from fitness maximization towards the development of models of evolved proximate mechanisms that may have maximized fitness in the past but lead to deviations under present conditions. To test the model we use data from a representative sample (...) of 7,107 men living in Albuquerque, New Mexico, between 1990 and 1993. The model we test proposes that low fertility in modern settings maximizes number of grandchildren as a result of a trade-off between parental fertility and next generation fertility. Results do not show the optimization, although the data do reveal a trade-off between parental fertility and offspring education and income.We propose that two characteristics of modern economies have led to a period of sustained fertility reduction and to a corresponding lack of association between income and fertility. The first is the direct link between costs of investment and wage rates due to the forces of supply and demand for labor in competitive economies. The second is the increasing emphasis on cumulative knowledge, skills, and technologies in the production of resources. Together they produce historically novel conditions. These two features of modern economies may interact with evolved psychological and physiological mechanisms governing fertility and parental investment to produce behavior that maximizes the economic productivity of lineages at the expense of fitness. If cognitive processes evolved to track diminishing returns to parental investment and if physiological processes evolved to regulate fertility in response to nutritional state and patterns of breast feeding, we might expect non-adaptive responses when returns from parental investment do not diminish until extremely high levels are reached. With high economic payoffs from parental investment, people have begun to exercise cognitive regulation of fertility through contraception and family planning practices. Those cognitive processes maynot have evolved to handle fitness trade-offs between fertility and parental investment. (shrink)

This paper lays the groundwork for a theory of time allocation across the life course, based on the idea that strength and skill vary as a function of age, and that return rates for different activities vary as a function of the combination of strength and skills involved in performing those tasks. We apply the model to traditional human subsistence patterns. The model predicts that young children engage most heavily in low-strength/low-skill activities, middle-aged adults in high-strength/high-skill activities, and older adults (...) in low-strength/high-skill activities. Tests among Machiguenga and Piro forager-horticulturalists of southeastern Peru show that males and females focus on low-strength/low-skill tasks early in life (domestic tasks and several forms of fishing), switch to higher-strength/higher-skill activities in their twenties and thirties (hunting, fishing, and gardening for males; fishing and gardening for females), and shift focus to high-skill activities late in life (manufacture/repair, food processing). (shrink)

Children may be viewed as public goods whereby both parents receive equal genetic benefits yet one parent often invests more heavily than the other. We introduce a microeconomic framework for understanding household investment decisions to address questions concerning conflicts of interest over types and amount of work effort among married men and women. Although gains and costs of marriage may not be spread equally among marriage partners, marriage is still a favorable, efficient outcome under a wide range of conditions. This (...) bioeconomic framework subsumes both cooperative and conflictive views on the sexual division of labor. We test hypotheses concerning marriage markets, assortative mating, and men’s labor motivations among Tsimane forager-horticulturalists of Bolivia and find that: (1) men and women both value work effort in marital partners, (2) marital labor contributions are complementary, (3) work effort is correlated between spouses, (4) total production is correlated with total reproduction, and (5) better hunters have higher fitness gains within marital unions. (shrink)

This paper examines social determinants of resource competition among Tsimane Amerindian women of Bolivia. We introduce a semi-anonymous experiment (the Social Strategy Game) designed to simulate resource competition among women. Information concerning dyadic social relationships and demographic data were collected to identify variables influencing resource competition intensity, as measured by the number of beads one woman took from another. Relationship variables are used to test how the affiliative or competitive aspects of dyads affect the extent of prosociality in the game. (...) Using a mixed-modeling procedure, we find that women compete with those with whom they are quarreling over accusations of meat theft, mate competition, and rumor spreading. They also compete with members of their social network and with those who were designated as cooperative helpers or as close kin. Women take fewer beads from desired friends, neighbors, and from those viewed as enemies. We interpret favoritism toward enemies as resulting from fear of retribution. Our results suggest that social relations among women are multifaceted and often cannot be simplified by exclusive focus on genetic relatedness, physical proximity, or reciprocity. We argue that a complex understanding of cooperation and competition among women may require important contextual information concerning relationship history in addition to typical features of resource ecology. (shrink)