[ExI] Forager lifespan

J. Stanton js_exi at gnolls.org
Fri Aug 12 19:23:36 UTC 2011

On 8/11/11 5:00 AM, BillK wrote:
> Current theory is that when pre-history humans were evolving they had
> a life expectancy of around 30 years, with 50 years being exceptional.
> More significantly, women had a lower life expectancy because of the
> dangers of continual childbirth. So the effect should be present less
> in women than in men.
> I don't see how evolution could have generated a beneficial effect in
> 70 year old humans at a time when 70 year old humans didn't exist.

It is a common mistake to assume average life expectancy is the same as 
average adult life expectancy.  Foragers have low average lifespans 
because of high infant mortality.  However:


"The average modal age of adult death for hunter-gatherers is 72 with a 
range of 68-78 years. This range appears to be the closest functional 
equivalent of an "adaptive" human lifespan."
"Illnesses account for 70 percent, violence and accidents for 20 
percent, and degenerative diseases for 9 percent of all deaths in our 
"Post-reproductive longevity is a robust feature of hunter-gatherers and 
of the life cycle of Homo sapiens. Survivorship to grandparental age is 
achieved by over two-thirds of people who reach sexual maturity and can 
last an average of 20 years. "


Also relevant:

"Between Zeus and the Salmon: The Biodemography of Longevity" (1997)

You can start reading at the above link.  One example: In the Hiwi, "In 
any case, once a child reaches adult age, the prospect of surviving to a 
reasonably old age is high. For example, a woman who reaches the average 
age of first reproduction (age 19) has about a 50 percent chance of 
reaching age 65.2.  This suggests that living well past the age of last 
reproduction is a common experience for human females."

And then:

Ages of death of a traditionally-living Inuit population during the 
years 1822 to 1836.  "Excluding infant mortality, about 25% of their 
population lived past 60...It's possible that life expectancy would have 
been higher before contact with the Russians, since they introduced a 
number of nasty diseases to which the Inuit were not resistant."


Unless we assume that modern foraging cultures underwent massive genetic 
selection for longevity since the spread of agriculture less than 10 
Kya, it seems likely that 70 year old humans did exist in meaningful 
numbers, and evolution could indeed have generated a beneficial effect 
in them.


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