The structure of energy production and redistribution among Tsimane\u27 forager-horticulturalists

This dissertation constitutes an integrated analysis of the Tsimane\u27 economic subsistence system. Its analyses are guided by a body of evolutionary theory which posits that life history traits, the structure of social relationships, and nature of economic production co-evolve in patterned and predictable ways. This theory specifically suggests that, for humans, the returns to embodied capital development and declines in reproductive efficiency late in life interact to produce: prolonged development, extended lifespan, menopause, and a predominantly downward three-generational system of energetic provisioning. The current analyses of Tsimane\u27 work effort, production, and transfers are consistent with this theory in the following ways. (1) Tsimane\u27 young remain in net caloric deficit until around age 20. From the 20s onward, both sexes produce a substantial net surplus, with men in middle adulthood producing the bulk of dietary fat and protein. The contributions of post-reproductive men and women to total productivity within the population are substantial even when mortality is taken into account. (2) The benefits of subsidizing young kin have predictable effects on individual workloads, and variation in these benefits interact with the time-paths of strength and skill acquisition to determine the life history of Tsimane\u27 resource production and transfers. Mothers decrease production with nursing children, but increase production with the presence of additional weaned offspring. Fathers and grandparents of both sexes also show greater productivity when more offspring and grandoffspring are present. (3) The life history of resource production leads to systematic differences in the benefits of receiving and the costs of giving calories across life, motivating net downward transfers between relatives across generations. Caloric transfers between families are predicted by the interaction of relatedness and relative caloric need. The analysis of transfers also reveals signatures of reciprocal consumption smoothing, and specialization and exchange across and within generations. The energetic approach taken in this dissertation complements existing demographic methods for evaluating the role of kin in promoting offspring success by directly examining the material means of investment in kin. Its results flesh out the structure of social relationships that constitute the core human pattern of cooperative reproduction

Quantitative Description of the Pastoral Economy of Western Tuvan Nomads

Nomadic pastoralism persists at a substantial scale in Tuva and neighboring regions of Inner Asia. Tuvan pastoral lifeways reflect adaptations to both local environments and current economic realities. Much of our quantitative understanding of the economics of Tuvan nomads is derived from data collected in the first half of the 20th century. Accordingly, this paper provides an updated picture of the inner workings of nomadic households using data collected in Barun-Khemchik and Bai-Taiga provinces in 2013–2015. It analyzes herd composition and size, and compares the frequency of different animals kept today with values recorded in Tuva in 1916 and 1931. It then quantifies rates of provisioning hay and grain, and the production of meat and dairy products for consumption and sale. Finally, it characterizes typical costs of food, petrol, medicine, clothing, and school supplies faced by present-day herders. We advocate the collection of quantitative ethnographic data that can shed further light on the future of the Tuvan pastoralist niche

Household Task Delegation Among High-Fertility Forager-Horticulturalists of Lowland Bolivia

Human kin cooperation is universal, leading researchers to label humans as “cooperative breeders.” Despite widespread interest in human cooperation, there has been no systematic study of how household economic decision making occurs. We document age and sex profiles of task delegation by parents to children ages 4–18 among Bolivian forager-horticulturalists. We test for sex differences in the probability of delegation and examine whether tasks are more likely delegated as household labor demand increases. We also test whether food acquisition tasks are more likely delegated to higher producers.We find mixed support for the prediction that girls are more likely delegated domestic and alloparenting tasks than boys (np173 children). Both sexes are more likely delegated tasks during rice harvest months; number of coresident young children is also associated with greater probability of delegated allocare, although the effect retains significance for girls only. For both sexes, father absence is associated with greater probability of delegation, particularly for food acquisition tasks. Children delegated rice harvesting achieve 45% higher mean daily caloric returns from harvesting than children not delegated harvesting. Our results therefore suggest that delegation increases household economic efficiency. We find mixed support for the hypothesis that delegation prepares children for sex-specific adult roles

From the Womb to the Tomb: The Role of Transfers in Shaping the Evolved Human Life History

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

Skills, Division of Labor, and Economies of Scale Among Amazonian Hunters and South Indian Honey Collectors

In foraging and other productive activities, individuals make choices regarding whether and with whom to cooperate, and in what capacities. The size and composition of cooperative groups can be understood as a self-organized outcome of these choices, which are made under local ecological and social constraints. This article describes a theoretical framework for explaining the size and composition of foraging groups based on three principles: (1) the sexual division of labor; (2) the intergenerational division of labor; and (3) economies of scale in production. We test predictions from the theory with data from two field contexts: Tsimane\u27 game hunters of lowland Bolivia, and Jenu Kuruba honey collectors of South India. In each case, we estimate the impacts of group size and individual group members’ effort on group success. We characterize differences in the skill requirements of different foraging activities, and show that individuals participate more frequently in activities in which they are more efficient. We evaluate returns to scale across different resource types, and observe higher returns at larger group sizes in foraging activities (such as hunting large game) that benefit from coordinated and complementary roles. These results inform us that the foraging group size and composition are guided by the motivated choice of individuals on the basis of relative efficiency, benefits of cooperation, opportunity costs, and other social considerations

Productivity Loss Associated with Functional Disability in a Contemporary Small-scale Subsistence Population

In comparative cross-species perspective, humans experience unique physical impairments with potentially large consequences. Quantifying the burden of impairment in subsistence populations is critical for understanding selection pressures underlying strategies that minimize risk of production deficits. We examine among forager-horticulturalists whether compromised bone strength (indicated by fracture and lower bone mineral density, BMD) is associated with subsistence task cessation. We also estimate the magnitude of productivity losses associated with compromised bone strength. Fracture is associated with cessation of hunting, tree chopping, and walking long distances, but not tool manufacture. Age-specific productivity losses from hunting cessation associated with fracture and lower BMD are substantial: ~397 lost kcals/day, with expected future losses of up to 1.9 million kcals (22% of expected production). Productivity loss is thus substantial for high strength and endurance tasks. Determining the extent to which impairment obstructs productivity in contemporary subsistence populations improves our ability to infer past consequences of impairment

Does Market Integration Buffer Risk, Erode Traditional Sharing Practices and Increase Inequality? a Test Among Bolivian Forager-Farmers

Sharing and exchange are common practices for minimizing food insecurity in rural populations. The advent of markets and monetization in egalitarian indigenous populations presents an alternative means of managing risk, with the potential impact of eroding traditional networks. We test whether market involvement buffers several types of risk and reduces traditional sharing behavior among Tsimane Amerindians of the Bolivian Amazon. Results vary based on type of market integration and scale of analysis (household vs. village), consistent with the notion that local culture and ecology shape risk management strategies. Greater wealth and income were unassociated with the reliance on others for food, or on reciprocity, but wealth was associated with a greater proportion of food given to others (i.e., giving intensity) and a greater number of sharing partners (i.e., sharing breadth). Across villages, greater mean income was negatively associated with reciprocity, but economic inequality was positively associated with giving intensity and sharing breadth. Incipient market integration does not necessarily replace traditional buffering strategies but instead can often enhance social capital

Health Costs of Reproduction are Minimal Despite High Fertility, Mortality and Subsistence Lifestyle

Women exhibit greater morbidity than men despite higher life expectancy. An evolutionary life history framework predicts that energy invested in reproduction trades-off against investments in maintenance and survival. Direct costs of reproduction may therefore contribute to higher morbidity, especially for women given their greater direct energetic contributions to reproduction. We explore multiple indicators of somatic condition among Tsimane forager-horticulturalist women (Total Fertility Rate = 9.1; n = 592 aged 15–44 years, n = 277 aged 45+). We test whether cumulative live births and the pace of reproduction are associated with nutritional status and immune function using longitudinal data spanning 10 years. Higher parity and faster reproductive pace are associated with lower nutritional status (indicated by weight, body mass index, body fat) in a cross-section, but longitudinal analyses show improvements in women’s nutritional status with age. Biomarkers of immune function and anemia vary little with parity or pace of reproduction. Our findings demonstrate that even under energy-limited and infectious conditions, women are buffered from the potential depleting effects of rapid reproduction and compound offspring dependency characteristic of human life histories

The Tsimane Health and Life History Project: Integrating Anthropology and Biomedicine

The Tsimane Health and Life History Project, an integrated bio-behavioral study of the human life course, is designed to test competing hypotheses of human life-history evolution. One aim is to understand the bidirectional connections between life history and social behavior in a highfertility, kin-based context lacking amenities of modern urban life (e.g. sanitation, banks, electricity). Another aim is to understand how a high pathogen burden influences health and well-being during development and adulthood. A third aim addresses how modernization shapes human life histories and sociality. Here we outline the project’s goals, history, and main findings since its inception in 2002. We reflect on the implications of current findings and highlight the need for more coordinated ethnographic and biomedical study of contemporary nonindustrial populations to address broad questions that can situate evolutionary anthropology in a key position within the social and life sciences

Paternal provisioning results from ecological change

Paternal provisioning among humans is puzzling because it is rare among primates and absent in nonhuman apes and because emergent provisioning would have been subject to paternity theft. A provisioning “dad” loses fitness at the hands of nonprovisioning, mate-seeking “cads.” Recent models require exacting interplay between male provisioning and female choice to overcome this social dilemma. We instead posit that ecological change favored widespread improvements in male provisioning incentives, and we show theoretically how social obstacles to male provisioning can be overcome. Greater availability of energetically rich, difficult-to-acquire foods enhances female–male and male–male complementarities, thus altering the fitness of dads versus cads. We identify a tipping point where gains from provisioning overcome costs from paternity uncertainty and the dad strategy becomes viable. Stable polymorphic states are possible, meaning that dads need not necessarily eliminate cads. Our simulations suggest that with sufficient complementarities, dads can emerge even in the face of high paternity uncertainty. Our theoretical focus on ecological change as a primary factor affecting the trade-off between male mating and parenting effort suggests different possibilities for using paleo-climatic, archaeological, and genomic evidence to establish the timing of and conditions associated with emergence of paternal provisioning in the hominin lineage