Longevity

Primates have long life spans compared to other mammals of the same adult body size, and great apes have the longest life spans of any primate except humans who can live about twice as long as the other great apes. Long human life spans are not a novelty of recent developments in public health and scientific medicine. Although life expectancy at birth was less than 50 years in human populations before 1900, that low average was the result of high rates of infant and juvenile mortality. A girl who survived to adulthood in historical populations, or in the traditional agricultural or hunting and gathering populations known ethnographically, was more likely than not to live past 50, and women reaching that age had, on average, an additional 15 or more years of life ahead. Whether this distinctive longevity evolved only with our own species or in other members of the hominin radiation, perhaps even the first members of genus Homo to expand out of Africa, is currently debated. Hypotheses to explain the evolution of distinctive human longevity highlight the contributions that older individuals make to the fertility and survival of their younger kin (see Grandmothering), and 2) novel aspects of human development prior to adulthood (see Childhood and Adolescence).