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Imagine a human being biologically immortal (cannot die from aging, illness, poisoning, etc...). How long would it take after its birth that there is a 99% probability that this human being has died from physical trauma (car crash, house fire, gun shot, lightning strike, meteor stike, etc...)? Thanks!
The answer is going to depend a lot on which society you are interested in. In the US, the Centers for Disease Control gives statistics on mortality causes, with an annual rate of 60/100,000 from all accidents. (That may not include homicide, but I think that adds only about 10/100,000.) So that extrapolates to about 1600 years as a typical lifetime if there were no other causes of death. Now if we approximate the distribution of deaths by saying that the odds of getting hit are independent of age and the same for each person, the surviving fraction would fall off exponentially. It would take very roughly 7500 years to have only 1% left.
In the environment in which our ancestors evolved, that time was much shorter. People were eaten by crocodiles, failed to recover from injuries, etc. One reason that there wasn't much natural selection for old-age good health was simply that hardly anybody would live long enough to make use of it.
(published on 01/05/2011)
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