Longevity

Primates show declines in most aspects of phenotypic performance with advancing age as do all species with separate somatic and germline tissues. Humans differ from other hominids in having longer life spans. Individual variation is substantial, but men and women can remain strong and healthy into their eighth decade, while the living great apes are usually classified as geriatric by the age of forty or earlier. Evolutionary theories of aging predict that rates of senescence will be faster when adult mortality is higher, and consistent with theory, many descriptions of aging great apes suggest that they age faster than humans do. By the late thirties chimpanzees move more slowly, appear to have stiffer muscles and joints, difficulties in climbing, and show declines in other aspects of physical performance associated with senescence in humans. In hunter-gatherer societies, life expectancies are usually less than forty, but that is due to high levels of infant and juvenile mortality. On surviving to adulthood, hunter-gatherer women remain strong and healthy through their sixties. Global census data show that national life expectancies were less than fifty until the twentieth century. Beginning in the mid-nineteenth century the global maximum life expectancy has increased steadily at a near constant rate of three months per year. Until the 1950s this increase was largely due to reductions in early life mortality. Since then marked reductions in late life mortality have continued to propel increases in maximum life expectancies. Whether these recent changes are due to disease, diet, and or health care practices that affect aging rates or to other as yet poorly understood population processes are topics of current research.