The Human Life Course and the Biodemography of Aging

Specific Aims Humans lived as hunter-gatherers for the vast majority of their evolutionary history (the genus Homo has existed for about 2 million years). Agriculture originated only 10,000 years ago and has been practiced by the majority of the world's population for just two or three millennia, a relatively brief period of time for selection to act. Anatomically modern humans evolved some 150,000-200,000 years ago. This means that natural selection on age profiles of physical function, morbidity and mortality hazards occurred largely in the context of a foraging lifestyle. Yet, very little is known about the aging process among hunting and gathering peoples. Modern hunter-gatherers are not living replicas of our stone age past. Global socioeconomic and epidemiological forces affect them all. Yet, in spite of the variable historical, ecological and political conditions affecting them, there is remarkable similarity in development and age-profiles of mortality among foraging peoples and other small-scale peoples that practice a mix of foraging and farming (Kaplan, Robson, and Lancaster 2003), and even the variation often makes adaptive sense. Their study can provide an important, if imperfect, lens on the life histories of our ancestors and the conditions that shaped the biology of human development and aging. It is almost certainly the case that at least some of the morbid processes leading to aging and increasing death rates with age among traditional subsistence peoples differ from those afflicting people in modern developed nations. Virtually all such populations exhibit growth stunting and low body mass indices, suggesting caloric stress. Most such peoples also engage in strenuous physical activities on a regular basis. There is also evidence suggesting that they experience higher rates of infectious disease (viral, bacterial, and parasitic) throughout infancy, childhood and adulthood. While there is a great deal of descriptive data about growth and other aspects of physical development during childhood in these societies, much less is known about the aging process across the lifespan and why it takes the form it does. The proposed research has three broad aims. The first is to conduct an integrated study of physical growth, development, aging, health and mortality in one population, the Tsimane’, a forager-horticultural society with little market involvement and access to modern health care. The second aim is to advance theory in the biodemography of the human life course, with a specific focus on aging and lifespan. The third is to lay the groundwork for collaborative, comparative research in human aging across a diverse array of ecological and social settings. The long-term goal of the research is to explain the age profile of human mortality and the rate at which humans develop and senesce in terms of economic productivity, muscular strength, endurance, body composition, disease resistance, and cognitive function.