In what sounds like a whole lot of hand waving (but hey! I study vision what do I know!), scientists have 'discovered' that creepy old men running after their daughters friends has led to an increase in life expectancy for human kind. Just think that people like Woody Allen, Jerry Seinfeld, David Letterman, and Michael Jackson have led to your grandma living a much longer life. Ok.. maybe not M.J. since he likes little boys and they don't have babies but Woody Allen - totally!
Human ability to scale the so-called "wall of death"--surviving beyond the reproductive years--has been a center of scientific controversy for more than 50 years, Puleston said. "The central question is: Why should a species that stops reproducing by some age stick around afterward?" he said. "Evolutionary theory predicts that, over time, harmful mutations that decrease survival will arise in the population and will remain invisible to natural selection after reproduction ends." However, in hunter-gatherer societies, which likely represent early human demographic conditions and mating patterns, one-third of people live beyond 55 years, past the reproductive lifespan for women. Furthermore, life expectancy in today's industrialized countries is 75 to 85 years, with mortality increasing gradually, not abruptly, following female menopause.
If you want much much much more detail than I've ever seen in a press release head on over to Science Blog for the excruciating details.
And if you want the perfect example of a creepy old man here you go, Family Guy Style!
the grandmother hypothesis = awesome