Sluggish Parents and Their Full-Throttle Offspring

I need caffeine. But my 7-month-old son clearly does not. He starts every day at full throttle, slowing down only for the occasional nap.

That got me thinking: Why has evolution given children so much energy and their parents so little?

So I asked Michael Rose. He's the father of four children. He's also an evolutionary biologist at the University of California, Irvine.

"It's fairly clear that human evolution has been strongly shaped by very powerful selection pressures over the last two million years to build a bigger brain," Rose told me.

That bigger brain doesn't have much in it when we're born, Rose says. So children need all that energy to explore the world and devour information.

"Play and activity and doing all kinds of things -- including things your parents and teachers don't like -- is a big part of developing a functional human brain," Rose says.

Brain development pays off in the long run. Kids eventually get smart enough to survive on their own.

But while they're going full speed through childhood, they put themselves at risk. So evolution has equipped children with parents -- who are slower but perhaps wiser.

Steven Lima of Indiana State University knows a lot about the value of parents. He's an expert on predators and prey. He says that, evolutionarily speaking, energetic children make easy prey.

"They spend a lot of time rough-housing, running around screaming and all this sort of thing," he says. "This is one of the most ridiculous things you can do. It's a giant 'Eat at Joe's' sign, you know. 'Just come kill me. I'm running around and not paying attention and making a lot of noise.'"

Parents are much more alert to danger, even if we're not very perky. So we keep an eye out for things like tigers and traffic.

And eventually, Lima says, children grow up and start acting more like parents.

"Playing around like that becomes ridiculous," he says. "You don't get anything out of it anymore. It just becomes dangerous."

What slips away, of course, is youthful energy.

UC Irvine's Michael Rose says he's reminded of that each year when incoming students arrive on campus.

"In terms of your ability to get up and go and do things, you can't beat an 18-year-old when they're motivated," he says. "It's strictly downhill from there. And I've experienced a lot of that downhill myself."

Me, too. And sometimes it takes a jolt of caffeine to temporarily slow the descent.

But there's an upside to having less energy: It means we don't take as many risks. And that improves our odds of living long enough to influence the next generation.

"Fifty- and 60-year-old humans can be very relevant to the future of their offspring and grand-offspring," Rose says. "And for that reason, natural selection may indeed still have some force in keeping us alive in middle age."

Provided we don't fall asleep on the job.

So as a father, I know that coffee isn't just about the buzz. It's about preserving the future of our species.