It took a few million years for human ancestors to evolve into the walking, talking, texting and blogging creatures we've become. Along the way, the human body and brain have changed a lot. And we couldn't have done it without our feet.
Our ape-like ancestors had a foot built for grasping branches and climbing trees. But our foot is stiff, taut and springy, built for walking and running.
Brian Richmond, an anthropologist, runner and kids soccer coach, is trying to find out how our unique appendage evolved.
At his office at George Washington University, Richmond has some tantalizing clues to how the change took place.
"These are the earliest footprints of early humans," he says, showing me an image of a track in what looks like dried mud. They were left in the African mud by one of our ancestors -- 1.5 million years ago. It's about a size 9.
And there's more than one; there's a whole trackway. The prints look like the diagrams of feet that dance instructors use to show how to do the salsa or the tango.
These Kenyan prints are the kind of discovery that makes a scientific career. For me, and I suspect for Richmond, they're even more exciting to behold than a bone or even a skull that old, because they represent an ancient action -- a living moment -- captured.
"A fossilized footprint is basically fossilized behavior," Richmond says. "It shows you what that individual did 1.5 million years ago that instant in time."
And what do those prints tell Richmond? "Sure enough, they were walking with a long stride, they had an arch in the foot the way we have."
Long legs and an arch in our foot. Our primate cousins -- gorillas, chimps, bonobos -- are flat-footed with no arch. The arch is actually the manifestation of a very complex apparatus inside our foot -- an apparatus for walking like no other in the world.
Richmond is trying to determine when humans developed these marvelous feet. He's doing it by working backwards, comparing our feet now to the climbing and grasping feet of apes and the feet of our early ancestors.
Blue-gloved and white-coated, Richmond leads the way into a brightly lit room at the GWU medical school. Metal gurneys are lined up in neat rows, each covered with a steel lid.
"I look at the human body and see how it's put together from a functional perspective and an evolutionary perspective," he explains. "I look at how it is different from other primates."
Richmond lifts a steel cover. Underneath, a cadaver lies pale and heavy, the head shrouded in gauze. In death, these donated bodies are instruments of learning. Richmond lifts a flap of skin -- the sole of the foot -- with a metal probe.
"So here I've just pulled the skin back, and here you can see one of those characteristics that's really uniquely human, and that is the long tendon that runs from the heel, underneath the skin, forward, all the way to the base of the toes." It's called the plantar aponeurosis. It's a flat, broad tendon, whitish and taut. Along with spring ligaments, it gives the foot its arch and its stiffness.
Imagine a thick rubber band stretching from your toes to your heel. Step down and the rubber band stretches and absorbs energy. As you roll forward, it transfers weight to your toes. And when the tendon snaps back, it even returns some of the energy in each step back up your leg.
We also have short toes, and a big toe that's in line with the other toes -- also for better walking and running.
So, when did this elegant appendage evolve? The Kenyan prints seem to show an arched foot. And that was 1.5 million years ago -- so sometime before that.
But footprints also reveal a lot about how a person walks: their posture, their stride, even the angle of their leg bones. So Richmond is filming people walking in sand and comparing their footprints to the Kenyan ones. "So that when we have a footprint," he says, "we can work backward and reconstruct what the steps were like in that individual, even at 1.5 million years ago."
If they're similar, then those ancestors probably were built -- and walked -- much like we do. If they're not, Richmond may learn how they were different.
This is where graduate student Kallista Bernal comes in.
"I'm standing here while they're trying to put these reflective markers on my joints," Bernal explains.
We're in a windowless laboratory at GWU. There's a 4-by-8-foot sandbox in the middle of the floor. Bernal is dressed in tights and a T-shirt, getting ready to walk the walk. "Can I wear a toe ring?" she asks.
No toe rings, but more than a dozen reflective markers are stuck to her hips, legs and her bare feet. She will walk through the sandbox as cameras focused on those markers produce a sort of stick-figure computer animation of her gait -- the turn of her ankles, the angle of her thighs, even the curl of her toes.
"Each footprint that I make, we're going to do 3-D scans, and try and figure out, based upon how I move and in what type of sediment I step in, how my footprints change," she says.
She gets the go-ahead and strolls through the sand as casually as she can under the watchful eyes of several researchers and a row of cameras. She leaves a nice set of prints in the sand. Richmond measures them with a laser and photographs them.
It's seat-of-the-pants science -- there's no precedent for it. And Richmond isn't sure what he'll find out. He needs to analyze hundreds of prints to make good comparisons between us -- that is, Kallista Bernal -- and the Kenyan ancestor.
Evolving Into Us
That ancestor was probably Homo erectus, which emerged about 1.8 million years ago. They made tools, hunted, used fire and were taller and had a bigger brain than their predecessors.
"They were starting to change their way of life," Richmond says. "They would go much farther. And a lot of people think it's mainly in terms of finding meat, and meat became a new and important part of the diet. That also led eventually to us populating the world more."
Eventually, Homo erectus evolved into us, modern humans. And we can thank them for inventing that spring in our step that gave us -- literally -- the get-up-and-go to hunt, to populate Africa and eventually to walk ourselves all over the world. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.