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 high‐fertility, 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.

Cognitive performance is characterized by at least two distinct life course trajectories. Many cognitive abilities (e.g. “effortful processing” abilities including fluid reasoning, and processing speed) improve throughout early adolescence and start declining in early adulthood, while other abilities (e.g. “crystallized” abilities like vocabulary breadth) improve throughout adult life, remaining robust even at late ages. Although schooling may impact performance and cognitive “reserve”, it has been argued that these age patterns of cognitive performance are human universals. Here we examine age patterns of cognitive performance among Tsimane forager-horticulturalists of Bolivia, and test whether schooling is related to differences in cognitive performance over the life course to assess models of active vs. passive cognitive reserve. We used a battery of eight tasks to assess a range of latent cognitive traits reflecting attention, processing speed, verbal declarative memory and semantic fluency (n=919 individuals, 49.9% female). Tsimane cognitive abilities show similar age-related differences as observed in industrialized populations: higher throughout adolescence and only slightly lower in later adulthood for semantic fluency, but substantially lower performance beginning in early adulthood for all other abilities. Schooling is associated with greater cognitive abilities at all ages controlling for sex, but has no attenuating effect on cognitive performance in late adulthood, consistent with models of passive cognitive reserve. We interpret the minimal attenuation of semantic fluency late in life in light of evolutionary theories of post-reproductive lifespan, which emphasize indirect fitness contributions of older adults through the transfer of information, labor and food to descendant kin.

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Human paternal investment, and that of many other species, is facultatively expressed and dependent on a diverse array of individual, social, and ecological conditions. Well-documented are the various ways in which men invest in offspring and the household. Specifically, local ecology structures pay-offs to male investment and has been shown to be an important predictor of the sexual division of labor. However, while variability in paternal investment has been well-characterized cross-culturally, plasticity within a group in response to changing socioecological conditions remains largely unstudied. To address this, we use recent economic development and market access to explore how changes in socioecology alter behavioral options for men and their resultant investment decisions. Among the monogamous Maya, we find that, associated with the introduction of novel subsistence opportunities and incentives for intensified paternal investment, fathers spend more time in the household, more time in domestic activities and more time interacting with their children. The changes in paternal investment documented here are largely contingent on four conditions: increased efficiency in subsistence brought about by mechanized farming, limited opportunities to engage in wage labor, increased opportunities to invest in offspring quality, and a monogamous mating system. Thus, Maya fathers appear to repurpose found time by furthering investment in their families.