Life Expectancy And Human Development In The 21st Century
Life expectancy is one of the best measures of human development. In hunter-gather societies, on average, about 57-67% of children made it to 15 years. Then 79% of those 15 year-olds made it to 45 years. Finally, those remaining at 45 years could expect to reach around 65-70 years. So we can see that life expectancy at birth in these societies was very low, given high child mortality. But some 40% did make it to about 65 years on average. It seems to have been worse in the class-based feudal and slave societies. The average medieval life expectancy for a peasant was only a mere 35 years of age at birth, but it was closer to 50 years on average for those who made it beyond 15 years.
You can see that measuring life expectancy at birth is not a perfect guide to how long humans did live in pre-capitalist societies. Nevertheless, there is no doubt that life expectancy on average rose sharply once science came to bear on hygiene, sewage, knowledge of the human body, better nutrition etc.