Photo: R. Bruce Montgomery
Footprints found preserved in volcanic ash in Tanzania, show that humans have been walking heel-to-toe for at least 3.6 million years.
But our feet have changed over the years, with early bipeds appearing to have had rigid feet that were proportionally much longer than ours today — about 70 percent the length of their femur, compared to 54 percent in modern humans. While modern humans held on to heel-first walking, University of Arizona anthropology researcher James Webber suggests our toes and feet may have gotten shorter, proportionally, as we became better runners to pursue prey.
"When you're running, if you have a really long foot and you need to push off really hard way out at the end of your foot, that adds a lot of torque and bending," Webber says. "So the idea is that as we shifted into running activities, our feet started to shrink because it maybe it wasn't as important to be super-fast walkers. Maybe it became important to be really good runners."
Webber published a study in the Journal of Experimental Biology that explores why humans walk with a heel-to-toe stride, while many other animals — such as dogs and cats — get around on the balls of their feet. As a barefoot runner, Webber lands on the balls of his feet instead of his heels when he runs.
"Humans are very efficient walkers, and a key component of being an efficient walker in all kinds of mammals is having long legs," Webber said. "Cats and dogs are up on the balls of their feet, with their heel elevated up in the air, so they've adapted to have a longer leg, but humans have done something different. We've dropped our heels down on the ground, which physically makes our legs shorter than they could be if we were up on our toes, and this was a conundrum to us."
When humans walk, Webber says, they move like an inverted swinging pendulum, with the body essentially pivoting above the point where the foot meets the ground below. As we take a step, the centre of pressure slides across the length of the foot, from heel to toe, with the true pivot point for the inverted pendulum occurring midfoot and effectively several centimetres below ground. This, in essence, extends the length of our virtual legs.