Life history, biodemography, health and aging
NIH/NIA grant R01AG023119-01, 2004-2010:
"The human life course and the biodemography of aging."
Project description
NSF grant BCS-0422690, 2004-2009:
"Grandparenting and the evolution of post-menopausal lifespan."
Project description
NSF grant BCS-0136274, 2002-2005:
"Growth, development, aging and sociality of the Tsimane of Bolivia."
The evolved human life history is unique in several fundamental aspects: 1) a long juvenile development period, 2) an exceptionally long adult lifespan, 3) support of offspring by post-reproductive individuals, 4) male subsidizing of female reproduction by food provisioning, and 5) a large brain and its capacities for learning. It is proposed that these unique features are co-evolved responses to a dietary shift towards high-quality, nutrient-dense, and difficult-to-acquire food resources. High levels of knowledge, skill, coordination, and strength are required to exploit this suite of high-quality, difficult-to-acquire resources humans consume. The attainment of those abilities requires time and a significant commitment to development. This extended learning phase during which productivity is low is compensated by higher productivity during the adult period, and subsidized by an intergenerational flow of food from old to young. Since productivity increases with age, the time investment in skill acquisition and knowledge leads to selection for lowered mortality rates and greater longevity, because the returns on the investments in development occur at older ages. The theoretical and empirical results obtained to date generate a series of hypotheses and new research questions this project is designed to test and answer.
The first objective is to advance theory in the biodemography of the human life course and test predictions regarding adult mortality and senescence. Higher "extrinsic" mortality should associate with more rapid senescence because the force of selection declines with age and any decreased probability of reaching adulthood should lead to investments in earlier reproduction and survival at the expense of somatic maintenance and repair.
The second objective is to test hypotheses about the roles of the brain and learning as determinants of the length of juvenile dependence and the transition to adulthood. The research will test the hypothesis that skills and knowledge are more important determinants of foraging success and horticultural productivity than strength. The research will also determine how childrearing practices and knowledge change with age and parity among women.
The third objective is to relate age-profiles of development and senescence in physical condition, morbidity and mortality, and behavior. One fundamental insight derived from recent theoretical and empirical results is that the timing of development co-evolves with adult mortality patterns and senescence, requiring a whole life course analysis. A second insight is that different domains of development and senescence such as physical condition, immune function, cognition and behavior co-evolve and are linked in time.
The fourth objective is to investigate the relationship between life history characteristics and resource flows within and among families. Foragers, especially those with large families, cannot support themselves and there is a net positive resource flow from smaller to larger families. In fact, the phase in the family lifecycle when parents are in their late forties and fifties requires net inputs from younger families and older post-reproductive individuals; thus, the long-term juvenile dependence and adolescent growth spurt could not have evolved without among-family resource flows. The research will investigate food sharing within and between families and will focus on how the adolescent growth spurt is subsidized. It will also focus on the intra-household division of labor and the allocation of tasks to individuals.
The fifth objective is to examine the effects of increased acculturation and integration into national society on health outcomes and the aging process.
The sixth objective is to stimulate collaborative comparative research on aging in a diverse array of ecological settings. No traditional society can represent the range of variation experienced by our ancestors. It is necessary to conduct comparative research to determine the universal and variable features of human life histories under traditional conditions and to investigate the effects of local conditions and integration with national society.
