Geezer Power: Older Men + Younger Women = Longer Lifespan

Sept. 18, 2007 — -- Scientists think they've found one of the reasons why humans defy evolution theory and live well beyond their reproductive life. It's all those old guys latching on to younger women and passing their good genes down to their kids.

No kidding.

For decades now evolutionary biologists have argued over a conundrum. There isn't much reason for members of any species to hang around after they can no longer reproduce, because according to theory they've already fulfilled their role in life. But humans tend to stick around for a long time after their traditional childbearing years are over.

Years ago the issue caught the attention of one of the pillars of evolutionary biology, William Hamilton, who died in 2000 after contracting malaria during a biological expedition to Africa. Hamilton wrestled with what came to be known as the "wall of death." Once reproduction ends, according to the wall theory, any biological system winds down abruptly.

Hamilton argued that when an organism stops reproducing, it is more susceptible to mutations that reduce its chances of survival. Thus death should come quickly. But all he had to do was glance around his home in England to see that there was something wrong with his own theory. People weren't dropping dead after females entered menopause. So Hamilton started looking for other factors that might influence human longevity.

One of the theories that came out of that is the "grandmother hypothesis." In early human history, some older women made themselves useful by helping their daughters, and even their granddaughters, raise their kids. That helping hand gave the kids a better chance to survive, thus preserving and ultimately passing along some of grandma's genes.

And since grandma lived long enough to help raise her great grandkids, then she must have had some pretty good longevity genes.

Makes sense, and several other studies over the past few decades continued to focus on the role of women in human longevity, since there is somewhat of a consistency in the age when women stop reproducing.