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Comment by mlyle | Hacker News Reader

> Selective pressure does not operate after the reproductive phase of life.

Even if we don't know the exact mechanism, it seems like we have evolved a longer lifespan in a safe environment than any other ape, while our lifespan in the wild was probably comparable to many apes.

Whether this long lifespan after reproductive age was selected for directly (e.g. grandmother hypothesis or patriarchal effect), or whether it happened because of some other evolutionary accident, it seems to be real.

Lowe points out here that there's a rebalancing of blood composition that happens later in life that would likely have been beneficial in the past, which is (very weak) evidence for a selective pressure that increased post-reproductive lifespans.

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Mice in the wild have a lifespan of roughly 365 days. Divide by ten to get life expectancy for humans “in the wild”. Mice living in a sheltered vivarium (but with pathogen exposure) make it out to 600 to 700 days. Mice in a specific-pathogen free vivarium routinely get to 700 to 900 days. Divide by ten again to get life expectancy of humans in a supportive “healthy” environment with some medical support.

From this point of view, mice live roughly 2.5X their reproductive lifespan; very similar to human post-reproductive lifespan.

There is nothing unusual or special about human lifespan, or even maximal longevity. Some normal mice (not growth hormone mutants) make it out to 1400 days.

The heritability of life expectancy increases with age in both mice and humans. Or crudely put—bad luck kills you in youth; bad alleles kill you in old age.

> long lifespan

...isn't it just better healthcare and nutrition?

2,000 years significantly fewer people reached 90+ as a percentage of the population, but it still happened.

We have done quite a lot in terms of infant mortality, but relatively little to extend the maximum age people reach. Take 1,000 random people born 100 BC vs 1,000 people born in 1900 and the oldest person from 1900 will very likely have lived longer but probably less than 10 years longer.

No, that increases the survival rate, but it's been documented for thousands of years at least that the "natural" human lifespan is over 70.

Mean lifespan has been dragged down mainly because of high rates of infant mortality and, as you allude to, various untreatable diseases. But as we make progress on those, the mean has been shifting up.

Living longer can be advantageous as you can take care of your children and grandchildren for longer, as well as continue to amass resources after the reproductive age, but indirectly improving the chances of your descendants.

It's easy to forget in modern society, but in tribal society the elders were fountains of wisdom. When computers, reference materials, technical documents, libraries, school systems, etc don't exist, the value of lived experience goes through the roof.

Being able to consult the elders when the group faces perplexing problems (who may have lived through something similar, or at least heard stories from the recently deceased generations who have) might mean the difference between between 20% of the population starving and no one starving.

This is all true but these indirect effects are generally too weak to actually modify allele frequencies in humans. These so-called grandmother effects were probably more forceful in the hunter-gatherer phase of human evolution—but even then may have been weak.

Like the gay uncle hypothesis. (-;

Yes!

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