An engineering masterpiece

Millions of years of evolution led to the marvel of the modern foot

January 19, 2007|By Susan Brink | Susan Brink,Los angeles Times

Orthopedic surgeons and podiatrists who study it, operate on it and care for it are as enamored of the often-sweaty, sometimes-stinky foot as are cardiologists of the heart, or neurologists of the brain.

"It's ingenious," says Edward Glaser, a Tennessee podiatrist who switched professions from mechanical engineering to podiatry because of his admiration for the foot's function. "As a machine, it's an engineering marvel."

The foot is built to walk on everything natural - grassy knoll, pine needle forest floor, volcanic rock - uphill and down. It is constantly balancing, changing direction and absorbing a pounding equal to 3.5 times the body's weight, only to spring back in time for the next step.

With its 26 bones and 33 joints, the foot is a biomechanical masterpiece. "There's something wonderful about it," says Dr. Nancy Kadel, professor of orthopedics and sports medicine at the University of Washington. "It's a flexible shock absorber, then it's a rigid platform that propels you forward. It adapts to sand when you walk on the beach. Then you climb onto rocks to look at the tide pools, and it drapes over the rocks."

But as close as it is to perfection for locomotion, two modern environmental necessities stand in the way of allowing it to maintain its full nature-given glory: hard surfaces and the shoe.

For a walker, and more so for a runner, a steady diet of concrete asks a lot of that magnificently springy arch. By forcing it flatter, it shifts balance unnaturally. The effects are felt all the way through the foot, ankle, leg, hips and back. Add a pair of shoes for the toes to bump against, the heel to blister against, and you've got the potential to injure almost every bone, muscle and ligament in the body.

It took millions of years for the foot to assume its present shape, a shape it's held for millions more years. The rest of the body has adapted, finding its center of gravity over the spaced left, right footprints of walking and the straighter, in-line footprints of running. But the foot and its attached body parts have had mere thousands of years to adjust to a steady diet of cobblestone, wood surfaces and sandals - not to mention the relatively recent introduction of concrete, asphalt, loafers and stilettos.

To see what's happened in the evolution of the foot over several million years, try the old trick used to teach kids their left from their right hand. Stick the thumbs out as the back of the hand faces you. The one that forms the "L" is the left hand.

Now try it with your feet. Humans, who have an opposable thumb but a big toe that lines up with the other four, can't do it, haven't been able to do it for maybe 4 million to 6 million years.

The big toe, once sticking out to the side to help our hominine ancestors climb trees and grasp branches, eventually took its place in the lineup of toes, stabilizing the foot and allowing us to walk upright.

Not that the other toes don't matter. The baby to the middle piggy stand in a rigid line from heel to the toe tips, giving people support when standing still. The other two toes are loose, aiding in balance.

The earliest evidence that feet were ready to support us on their own, without help from the front paws, are the Laetoli footprints, a trail left by three human ancestors taking a stroll on two feet almost 4 million years ago. They walked together on soft ground, intermittently covered by volcanic ash and rain, leaving behind a bipedal record that hardened like a plaster of Paris science project. The footprints were discovered in Tanzania in 1976 by a team led by paleoanthropologist Mary Leakey.

Another clue to how long humans have been upright are the fossilized remains of Lucy, discovered in Ethiopia in 1974. Her remains are from about the same time as the Laetoli footprints, give or take half a million years. But the bones in Lucy's wrists, according to research by scientists Brian Richmond and David Strait of George Washington University, suggest that, while she herself didn't walk on all fours, she retained some of the bone structure that allowed for knuckle walking. Bones from her wrists, the researchers found, remained rigid enough to help support her body on all fours.

Gaps in the fossil record don't allow for pinning down exactly when hominids stood up and walked on two feet. "Estimates vary, but most experts would put this transition at about 6 million years ago," says Thomas Greiner, professor of anatomy and physical anthropology at the University of Wisconsin at LaCrosse.

That's about when our human ancestors made the biological commitment to give up the advantages of an opposable toe for the alternative advantages of having two hands free to hunt and gather. "I think the human foot is essentially an organ that was designed first for grasping, but that has been modified for support and propulsion of the human body," Greiner says.

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