Image via Christoffer Undisclosed on Flickr.
There you are, strutting down the street all arrogantly, showing off the fancy feet you've evolved in order to walk on two legs. "Look at me go!" you shout at the squirrels, whose own feet are still designed to climb trees. "Ha, how out of date," you scoff, stoked on your own uniqueness. There's only one problem: You're not as special as you think.
By declaring that our human feet are not as special as we once thought, a new study out of the University of Liverpool has made the list of uniquely human characteristics shorter yet again. The study, released yesterday in the Proceedings of the Royal Society B, demolishes a decades old dichotomy that posits that humans and apes are very different from the feet on up.
Established over seventy years ago, the historic perspective sees the human foot as incredibly stiff in comparison with that of tree-dwelling great apes. “The traditional view is probably based on the preconception that humans must be very different from other apes,” said Robin Crompton, a professor of musculoskeletal biology and one of the researchers on the Liverpool team. “It’s an idea which is outdated, but taking a long time to die.”
To tackle this ingrained perception, Crompton and his colleagues compared the function of the mid-feet of humans and certain apes, namely bonobos and orangutans. For humans, they used a pressure-recording treadmill, which allowed them to acquire data on over 21,500 human footfalls from among forty-five “modern Western” subjects. Bonobo and orangutan information was obtained by walking the animals over specialized plates at their zoo enclosures.
This figure from the paper compares the ratio of mid-foot pressure to max foot pressure of humans and non-human test subjects, along with pressure maps of (b) bonobos, (c) orangutans, and (d) humans. The key finding is that while humans exert less pressure on their mid-foot (we have stiffer arches after all), that the trends overlap suggests that our feet are more similar to apes' than previously thought.
They discovered that our feet, while comparatively stiff, are still remarkably flexible. In fact, the variations seen in our footsteps overlap significantly with the variation seen in non-human apes, including the orangutan, which the researchers note is “the most arboreal great ape.” This means that after all this time we’ve spent dwelling on the ground and not in trees, we still retain some of the elasticity in our feet that goes along with hopping between branches.
On a philosophical level, these results acknowledge humans to be “just another ape.” Beyond that, they also have ramifications for the study of aging and chronic disease, specifically osteoarthritis and diabetic foot. According to Crompton, the work is “directly relevant to diagnosis and treatment of both conditions.” And as for what this means on a day-to-day basis, Crompton suggests you think about how ape-like your feet are next time you head out to Payless. “Our feet are designed to be flexible and we should think about that when we pick shoes!”
So what happens now in this foot saga? Well, the major question is why, after so many thousands of years of evolution, we still have feet that are ready for the trees. Crompton thinks it’s probably because that same flexibility is good for walking or running over irregular terrain. Delving into this hypothesis will be one of the next steps.