First Demographic Transition, From the Pleistocene to the 18th Century

Abstract

The first demographic transition underlying the evolved biology of aging in our species has a long evolutionary history. The demographic transition to longer lives in humans compared to other great apes accompanied important changes in (1) diet; (2) the timing of ontogenetic development; (3) reproductive schedules; (4) the role of women and men in provisioning children; and (5) age profiles of energy net energy production. There is evidence suggesting that the systematic divergence began some time during the early Pleistocene, 2–1.5 million years ago. The goal of this article is to review the evidence on this transition in a way that sheds light on the evolution of human aging with a particular focus on middle and old age. This evolutionary history is directly relevant to understanding chronic disease and age-related declines in function among people living today. The available evidence suggests that living past middle age was not rare before the transition to domesticated foods in the Holocene, and that individuals who lived into old age made significant contributions to the gene pool of future generations. Individuals in middle and old age played important economic and childcare roles, partially subsidizing their children's reproduction and feeding their grandchildren. These facts imply that our species is adapted to a long lifespan, and that there has been significant scope for natural selection to act on the aging process during the post-reproductive phase of life. Similarities and differences derived from epidemiological comparisons of subsistence populations with western populations sheds important light on the fundamental biology of aging and novel changes in patterns of aging that are due to lifestyle.