Bipedalism's Message
Today, we walk on two legs. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
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Long ago in this series, I wrote that “We humans live in varying states of unstable equilibrium. So when we walk, we achieve a brief unstable balance on one foot. Then we begin a non-equilibrium free-fall, and catch ourselves on the other foot. When we call someone unstable, we really mean that, after they enter free fall, they struggle to reach the next temporary equilibrium.”
Action of a human walking
That’s been hard for inventors to wrap their heads around. Not ‘til 1996 did Honda finally make a robot that could, on its own, sort-of replicate a human’s walk. Of course much clumsier walking robots had gone before. At this writing, thirty years later, robot sprinters have finally outrun the fastest humans. But not yet with our human fluidity of motion.
Birds reveal much about all this. We’ve gone beyond them in speed, altitude, and carrying capacity. Of course they far outstrip us in grace and beauty of flight. And in mode of flight – since we’ve yet to build a practical ornithopter.
Farmer Grawunder’s Ornithopter, Museum of 20th Century Technology
But they do teach us something about standing. We humans can stand on two feet for a long time -- always making tiny muscular corrections. But a bird might stand, at rest, all night on just one leg. Some of that standing takes minimal correction. And the flamingo, for example, is actually stable in a one-legged stance.
Flamingo standing on one leg
But we humans – well, when I was in the army, we sometimes had to stand at attention for half an hour. Before the end, we usually saw at least one of our number collapsing, partly from fatigue.
Still, our instability is part of so much of what we achieve. We’re a species for whom error and correction are bedrock. Once, I heard the great mathematician, George Pólya, lecture. And he stressed how we must learn to Guess and Correct.
We’re raised with quite the opposite mantra: “Do it right the first time.” No doubt we’d better do certain things right the first time – surgery or piloting an airplane. But that mantra was guaranteed to avoid doing anything creative.
So: back to walking. Early work on robotics sought to make walking a stable process. It took a long time to build in the seeming illogic that said walking begins with falling. Just as it’s hard for a calculus teacher to remember that real learning requires that we guess and correct. We accomplish so much when we first see things incorrectly – then correct until we set them right in our minds.
So now I’m about to walk over to the drinking fountain. And this time, I’ll bear in mind that I’m doing something essential – all the way from basic movement to the best of human creativity.
I’m John Lienhard, at the University of Houston, where we’re interested in the way inventive minds work.
(Theme music)
See this Radio episode: Equilibrium | The Engines of Our Ingenuity
Why Do Birds Stand On One Leg? (Everything Explained) | Birdfact
30 Years Ago, Robots Learned to Walk Without Falling - IEEE Spectrum
Chinese robot beats Usain Bolt's 100-meter sprint world record in humanoid bot games - CBS News
See also, World’s fastest humanoid robot runs 22 MPH - CyberGuy
The Mystery of the One-Legged Bird
polya.pdf This site describes Pólya’s Guess and Test ideas, although here, unlike his words in the talk that I heard, he uses the words Guess and Check.
Walking diagram courtesy of Wikimedia Commons. Photos by JHL
This Episode first aired September 22,2026.