Getting the Feel of Some Fancy Footwork

I recently wrote about feet--more specifically, about the importance of the big toe in effortless walking and standing. That got me to wondering: Why do we walk so much more proficiently than our chimp relatives?

To find out, I chatted with Dr. Joel Moorhead, an associate medical director in group insurance for Prudential Insurance Co. in New Jersey, who has written an article about foot evolution.

“Everyone thinks their feet are ugly, but when you think about how miraculous they are, they start to look pretty,” Moorhead enthuses. “They’re so functional; they’ve changed in such an amazing way from the time we were grabbing branches with our feet to the point where now we’re able to run marathons.” (Not me, but point taken.)

Chimps, when they walk, are doing a dicey balancing trick, Moorhead says. They plop one foot down--and balance. They plop the next foot down--and balance. That’s why they waddle when they walk.

Some of us know people whose walks are on the waddly side; some folks, in fact, are born with feet built a little more like chimps’ feet. But for the most part, our walking strategy is different. With each step, we fall forward. Then, in the nick of time, we save ourselves from landing face-first in the dust by pushing off again, using the stiff arch of our foot as a lever.

The stiffness of that arch makes our feet pretty useless in the trees, since we don’t have the flexibility to grab branches and swing from them--though my older brother Jonathan may be a primitive throwback. Well, do I remember, during family dinners, how one of his feet would reach out, grasp mine deftly, then drag me under the table. (Well, do I remember my father yelling at me for “horsing around” while Jonathan sat there eating politely, as if butter wouldn’t melt in his mouth.)

But--and Moorhead really likes this fact--even though our feet and chimp feet act in very different ways, in other ways they’re acting identically. Feet contain lots of muscles, and studies show that the same muscles, in the same pattern, are used whether it’s a chimp climbing a tree or a human stomping to the cafeteria for a mid-morning doughnut. The brain’s still sending the same instructions. But the structure of our feet has changed, so what we end up doing is different.

Moorhead’s interest in the evolution of walking doesn’t begin and end with the wondrous foot: He’s also interested in the back, which feels less than wondrous for many of us as we age. Walking upright could be one reason for those nasty back problems, Moorhead says, since it puts stress on the lower back--the part supported only by ligaments and muscles.

Evolution, he says, has been working on the problem: It’s shortened the unsupported part of the back. Monkeys have seven lumbar vertebrae. Great apes have six. We have only five. (I wonder how many Jonathan has.) In fact, some of us have even fewer: In them, the fifth vertebra is kind of reduced, as if our species is on the way to an even shorter-backed state.

Evolution: It ain’t over yet.

Information at Your Fingertips

Talking of evolution, what about fingernails? I have no idea why the question popped into my mind--maybe from staring at my own grubby, unmanicured specimens--but the other day I wondered what they were good for. Moorhead’s not in the fingernail-pondering business, so I inquired elsewhere.

“Nobody knows the answer,” says Craig Stanford, a professor of anthropology at USC. But he notes that all higher primates have flat nails like ours. Claws, he says, would get in the way of the ability of our opposable thumbs to do all the dandy things they can do. (Anyone watching someone with super-long artificial talons peck on a keyboard or cash register will see the truth in that.) In other words, reduced, flat nails may have no benefit. They’re just not in the way like a claw would be.

“I don’t know of any ‘fingernail specialists’ out there,” adds Herman Pontzer, an anthropology grad student at Harvard. He hazards that the nails might be protective and help us apply force with our fingers. But for gripping things, evolution didn’t favor claws: It favored strong hands for holding on and hairless palms and fingerprints for friction.

Oh. So that’s why we have fingerprints.

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