This research follows a different course from the work of many who have searched for some link between the emergence of modern human anatomy, about 100,000 years ago, and the big changes seen in the structure of human society about 70,000 years later.
"A lot of people have tried to link the two," Caspari says. "But you don't see modern human behavior with the emergence of anatomical modernity. You see it much later."
"So perhaps what was needed was more ideas, and that can come from having a large number of people around," she says. As Lee suggests, you can store a lot more stuff on a bigger hard drive. But what could have caused such a dramatic leap in longevity?
Strength in Numbers
Caspari says there probably wasn't a single trigger, or single event, that increased the odds of living longer.
Most likely, she says, a few humans just lived a bit longer, for whatever reason, and the rest of the tribe discovered that it's good to have a few codgers in the camp. They could tend to the kids, freeing mom to paint on the walls of the cave. And sometimes they had been down the trail once or twice before and knew the safe way through harm's way.
So instead of casting the old folks off, they took care of them, and as they say, their numbers multiplied.
"All of this can happen very quickly," Caspari says. "When you think about the population growth that has happened in the last couple of hundred years, it's incredibly dramatic, and that's just a snap of the fingers. Think of the magnitude of that increase."
So with an increasing population, society began to grow more complex, leading ultimately to the eras of kings and bureaucrats, priests and science writers. We didn't get where we are just because of human evolution, she argues. It's the other way around.
"We have culture driving human evolution," Caspari says. There are far more of us because our ancestors decided there was strength in numbers.
Of course, with the planet's current population at 6 billion plus, and climbing, it's possible to overdo a good thing.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.