August 29, 2007
Our Life Expectancy Due To Old Men Seducing Young Women?

Some people profess to be disgusted by the sight of old men seducing young fertile women. But some biologists and anthropologists at Stanford University and UC Santa Barbara argue that the success of old men managing to impregnant younger women drove human evolution to extend human life expectancy.

Evolutionary theory predicts that senescence, a decline in survival rates with age, is the consequence of stronger selection on alleles that affect fertility or mortality earlier rather than later in life. Hamilton quantified this argument by showing that a rare mutation reducing survival is opposed by a selective force that declines with age over reproductive life. He used a female-only demographic model, predicting that female menopause at age ca. 50 yrs should be followed by a sharp increase in mortality, a “wall of death.” Human lives obviously do not display such a wall. Explanations of the evolution of lifespan beyond the age of female menopause have proven difficult to describe as explicit genetic models. Here we argue that the inclusion of males and mating patterns extends Hamilton's theory and predicts the pattern of human senescence. We analyze a general two-sex model to show that selection favors survival for as long as men reproduce. Male fertility can only result from matings with fertile females, and we present a range of data showing that males much older than 50 yrs have substantial realized fertility through matings with younger females, a pattern that was likely typical among early humans. Thus old-age male fertility provides a selective force against autosomal deleterious mutations at ages far past female menopause with no sharp upper age limit, eliminating the wall of death. Our findings illustrate the evolutionary importance of males and mating preferences, and show that one-sex demographic models are insufficient to describe the forces that shape human senescence.

Read the full research paper (free access at Plos One) for all the details.

Older Canadian men need to try harder to apply selective pressures for longer life. The brutal Amazonian Yanomamo men show this can be done.

Male fertility is nonzero till ages 55 yrs in Canada and the !Kung, 65 yrs in the Ache, 70 yrs in the Yanomamo, 60 yrs in the Tsimane, and 75 yrs in the Gambia.

So, look, you have a life expectancy that extends into the 70s or 80s because old guys managed to knock up young hot babe women. Is this upsetting? Disgusting? Reality can sometimes be that way (to quote Jello Biafra of the Dead Kennedys).

Nowadays the best ways to extend life are to develop great stem cell therapies and gene therapies. We should pursue those therapies with all the determination and gusto that old men of yesteryear (and of today) spent trying to bed young fertile women.

Update: As regular readers know, I try to look for practical ways to apply lessons I learn from reading about scientific progress. This report is no exception. I now feel obliged to knock up a beautiful woman once I reach 65 years old. I'm going to do it because I support eugenics for a longer lived human species.

Share |      Randall Parker, 2007 August 29 08:45 PM  Aging Studies


Comments
Stephen Gordon said at August 30, 2007 10:28 AM:

"I feel obliged..."

'cause that's just the kind of giving guy you are Randall. :-)

There's another mechanism that could have brought this about called the grandparent hypothesis.

If this is correct the advent of language would have seen a quick lengthening of human lifespan. With language information could be transfered. This created selective pressure to increase wisdom transfer time. Grandparent wisdom - "when I was a kid and there was a drought we march toward the sunset for three days to this lake" - could allow survival of longer lived groups to the inclusion of shorter lived groups.

The Grandparent hypothesis could have worked in concert with the Randy Old Man mechanism.

Nick said at August 30, 2007 6:17 PM:

I believe the grandparent hypothesis is prevailing at the moment.

There is a second mechanism for its operation: humans require extended juvenile care (especially as culture becomes more complex), which grandparents provided.

Randall Parker said at August 30, 2007 6:38 PM:

A study done on family records of Finnish people found that surviving grandmothers boosted baby survival of mothers. I think this study used data from previous centuries. Sorry, this is from faded memory, no link.

Hopefully Anonymous said at August 31, 2007 8:59 AM:

This could tie in nicely with observations that hierarchy, in and of itself, affects longevity. So hierarchically unsuccessful men die off sooner, and have less opportunities to procreate with fertile women. Which brings to mind an empirical question: do heirarchically successful women stay fertile longer?

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