On my morning commute, I was flipping through the stations when I heard a story on Y98 saying that scientist, because of evolutionary theory, men are now living longer because some of them take younger spouses. The way the host made it sound, because men could reproduce later in life, they are now living longer. The host went on to talk about his grandfather and great grand father having younger wives. There’s nothing like anecdotal evidence you know.
Being a shade tree evolutionary biologist™, I called bullshit on the whole thing. Evolution works on populations over generations, not on individuals, and it doesn’t matter if men CAN have children later in life, it matters if they DO have children later in life. Even if they do, it doesn’t affect their longevity, it just means that because they mated late in life, there is a chance that their children will have genes that will help them live long enough to mate later in life. Over many generations, if the older males are contributing significantly to the number offspring, then and only then would there be an evolutionary push for longevity.
I figured one of two things, either the hosts were mangling the contents of the article, or the article was total crap and not in a scientific journal. I wanted to call the station and tell them how wrong they were, but didn’t know the number. So of course when I got to work I googled the article.
Wouldn’t you know it, the radio host got it completely wrong. The scientist were not looking at why men are living longer now, they were looking for why MAN, as in men and women live past there reproductive years.
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.
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.
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.
Cedric Puleston, a doctoral candidate in biology at Stanford and a co-author of the study, said the researchers wanted to see if men also played a role in increasing the human lifespan.
“If men and women have different life histories, in terms of survival and reproduction, doesn’t it make sense to look at what’s going on in both sexes?” Puleston said. For help, Tuljapurkar and Puleston turned to a colleague, anthropologist Michael D. Gurven of the University of California, Santa Barbara. Gurven has compiled extensive records of longevity and fertility of several hunter-gatherer groups, including the Dobe !Kung of the Kalahari and the Ache of Paraguay, one of the most isolated populations in the world.These people live a lifestyle that is believed to be very similar to the hunter-gatherers in the earliest phase of human history. Probably not exactly, but it’s the best scientists have to work with.
Here is the key part though.
The research showed that in very primitive societies, men remained reproductive much later in life than women. They usually mated with women who were much younger, and they tended to do that over and over again. Male fertility tended to taper off with age, but it didn’t end suddenly as it did with women.
“That’s true in every population we looked at,” Puleston said. That continues to this day, with some men in their 80s siring children. Puleston said he knows of one man who became a father at 95.
Older men helped increase the birth rate in the population as a whole, because more old guys were remaining useful, and it also meant gramps was passing along a pretty good set of genes. And it’s not just a matter of passing on good genes.
“It’s probably more accurate to talk about a lack of bad genes passing on,” Puleston said.
That contributed to a longer human lifespan over centuries of evolution. Of course, grandma probably did her part, too. And cultural factors, like the availability of antibiotics, have helped extend longevity.
And in case you’re wondering about the radio host’s premise of taking a younger spouse making you live longer
By the way, the researchers note that it’s not going to add any years to an old man’s life if he takes on a young mate.
Technorati Tags: evolution, marriage