Ask any archaeologist. Most adult hunter gatherers did not make it to 40. We're not talking averages, we're talking maximum life expectancy...
The modal age of death for hunter gatherers that survived to adulthood ranges from 65 to 72 among the reasearched cultures.
Sure, a large proportion of them die at early childhood - "life expectancy" measures takes that into account by definition, as it measures the total average life expectancy; and if you get a 100 kids who live to 70 and 100 kids who die as infants, then the average life expectancy is 35.
Maybe you could present a paper? Because amongst most hunter gatherers researched the modal age is much lower...
M.Gurven & H.Kaplan Longevity Among Hunter-Gatherers: A Cross-Cultural Examination has a conclusion of "The average modal age of adult death for hunter-gatherers is 72 with a range of 68–78 years."
It's not about the ancient societies but is relevant because for this discussion the point is not history, but the effects of a hunter-gatherer diet.
http://www.anth.ucsb.edu/faculty/gurven/papers/GurvenKaplan2...
Re:A Call for a Low-Carb Diet
by MisterBastahrd on Tuesday September 02, 2014 @05:31AM
(#8256590)
Sure. They also had neither vaccinations nor antibiotics, had no understanding of bacteria, etc. Take any modern teenager and stick him back in the stone age and I doubt he makes it to 40 even WITH modern knowledge.
Most of the statistics about our ancestors having a 35ish life expectancy are skewed by high infant mortality, and high risk of death due to injury or other external ailments (a broken leg on the savannah can easily be a death sentence). A hunter-gatherer who surived those things would tend to live into their sixties or beyond.