Contemporary hunter-gatherers and human life history evolution

In this chapter, I use data from contemporary hunter-gatherers to argue that human life history fits a general mammalian pattern and needs little "special pleading. " Among hunter-gatherers, first birth occurs at the age we should predict for a great ape with a hunter-gatherer adult lifespan, so our long juvenile period needs no unique explanation. Archaeological demography, however, has suggested much higher adult mortality. I exclude modern influences on hunter-gatherer adult mortality and summarize problems in archaeological demography. Hunter-gatherer adult mortality resembles mortality in the rural third world and in historical pre-industrial populations. Because of the many accounts of special features of human growth (such as the adolescent spurt), 1 was surprised to find that Charnov's growth function (an essential piece of his general mammalian life history theory) accounted for most of the variance in Hadza growth between weaning and maturity. Hunter-gatherers and great apes (except gorillas) grow at the same rate. Young foragers have much to learn, but they seem able to learn it even when deprived of big stretches of their juvenile bush experience. Learning does not come to a halt when reproduction begins. We cannot argue that the human juvenile period is long because so much needs to be learned before reproduction. Effects of grandmothers on younger kin (demonstrated in sedentary populations) could account for elongated adult life. Older Hadza women (but not men) live where their help to younger kin (if effective) would most enhance their own fitness. The opportunistic mobility of older Hadza women may make their demographic effects difficult to see.