PDR 33.2 Gurven-Kaplan-FINAL.indd

AVERAGE WORLDWIDE HUMAN life expectancy reached 66 years in the first quinquennium of the twenty-first century, with extremes at the country level ranging from 39 years in Zambia to 82 years in Japan (United Nations 2007). Average life expectancy has increased linearly at almost three months per year over the past 160 years, with improvements in sanitation, nutrition, and public health accounting for much of this change (Riley 2001; Oeppen and Vaupel 2003). As a consequence of longevity in the developed world, women currently live more than a third of their lives in a post-reproductive state following menopause. Such high survival rates almost surely had never occurred before in human history. Agriculture and pastoralism have been practiced for only about 10,000 years, and most extensively in the past 5,000 years. The genus Homo has existed for about 2 million years, and humans have lived as hunter-gatherers for the vast majority of their evolutionary history. While some important genetic changes may have occurred in populations after the advent of agriculture, the major distinctive features of our species (Wang et al. 2006), such as large brains, long lives, marriage and male investment in offspring, long child dependency on parents, and grandparental support of grandchildren, appear to have evolved during our preagricultural history (see Kaplan 1997 for reviews; Kaplan et al. 2000, 2001). Despite recent improvements in human survivorship, it is likely that the age-specific mortality pattern and the timing and pace of development and senescence evolved during our hunter-gatherer past as well. The purpose of this article is to assess the evolved human mortality profile and particularly the pattern of senescent mortality change with age. We address five questions: