Why Walk on Two Legs?

As a Feldenkrais teacher who is fairly obsessed with understanding how to help my students and clients turn their walking into an elegant, efficient, and long-lived function, I was happy to attend a lecture in Feb, 2015 at the American Museum of Natural History (AMNH) on Manhattan's upper west side, called "Why Walk on Two Legs? The Pros and Cons of Bipedalism".  The panel of Museum Curator Brian Richmond and Boston University anthropologist Jeremy DeSilva held their discussion in front of a sold-out audience.  The topic: what did our species gain and what did it give up to achieve, what the famous orthopedic surgeon and author Adalbert Kapandji has called, "the near permanent miracle" of walking on two legs. 

The full talk is below.  

The enormous role that learning plays for humans in the development was not spoken of during the talk.  So I was glad I got to ask the first question during the Q&A portion of the evening (not recorded).  I asked:  

  1. Do chimps have a talus (ankle bone) like humans and how does this affect their ability to walk? (sort of, and greatly...)
  2. How long does it take a human to acquire the basic ability to walk compared to other animals? 

The answer to the second questions is: a very long time.  Walking takes usually several years to fully stabilize in humans.  Yes, a baby can walk for the first time at 12 - 14 months (give or take), but the function takes much, much longer to become reliable.  And because human beings rely so much more on learning to acquire their behavior, it is open to so many more influences both positive and negative.  In short, human learning is far more exposed to the errors of teaching, the corrosion of poor use, and the interruptions in learning.  Most other mammals arrive with their basic motor abilities intact, or arriving in short time.  A horse born in the morning, is, by the same evening, essentially up and walking/galloping the way it will for the rest of its life .  A baby born in the morning has about a 1,000 days of trial and error before its basic locomotive patterns will both emerge and stabilize.  

While waiting to speak with the panelists after the talk, I struck up a conversation with a neurologist who said he "sticks needles in people's muscles to find out if they're working right". He was waiting to talk to the panelists about the roll of the buttocks in running.   "You really don't need the buttocks for walking, but you do for running," he said.

I told him that I heard somewhere that an orangutan fires roughly 35% of his available muscle fiber when he does an action.  Humans are closer to 12-15%. This is why an angry orangutan can pull a door off it's hinges when he wants to. 

As to why would humans have such a small percentage of recruitment, here is my guess. 
The human upright posture on two legs is inherently unstable. This is our advantage. Think of the bull fighter vs. the bull.  The bull, on four legs, is very stable and has enormous power, and you would never want to be in front of one that's charging. But the bull has a very wide turning radius.  The bull fighter, if he's well trained, can spin around himself (his upright longitudinal axis) and avoid the bull at the last second.  

Our inherent instability means that we require very little power to move. Somewhere in the evolution to bipedalism we traded  stability and higher muscle fiber recruitment for instability and lower muscle fiber recruitment.  This is because if you're going to be up on two legs and very unstable, and you're going to take years to acquire the skill you need a high degree of sensitivity in the firing of the muscles.  In other words, we need an extraordinary sensitivity to the timing, orientation and manipulation of our organization.  We traded wired-in skill and stability, for uncertainty, learning and sensitivity. The result?  An adult male is able to wind up and throw a rock accurately at almost 100 mph (some of us) and this gives us an enormous kill zone.  With our heads and teleceptors placed at our highest point we can see around us, turn, and communicate all with incredible speed. We can strike at a distance with deadly accuracy like no other animal. Is it any coincidence that the improvement of weapons has trended towards striking and killing with greater accuracy at a greater distance? This arises out of the image of our own potency.

Watch the video of the human baseball pitcher and then the chimp trying to throw a rock.  The chimps tend to use a very inefficient homo-lateral style of throwing that gives them neither power nor accuracy. When I brought up the "kill zone" issue, another person waiting to talk to the panelists said that his brother had been in Africa and found him self being harrassed by a pack of chimps.  His friends tried shouting, threatening gestures, waiving their arms.  The thing that worked, he said, was throwing rocks at them...

So somewhere along the way our species traded quick guarantees of certain motor skills for uncertainty, instability, sensitivity and refineability, fixed patterns for infinite variability. 

Learning must be a damn valuable function. 

Watch this video of Dr. Feldenkrais lecturing at CERN. He begins speaking after the introduction at about the 1:55 mark. His opening question:  "Would we have a skeleton if there were no gravity?"

I look forward to your comments. 


Andrew Gibbons

Further Reading: 

  1. The Strength of Great Apes and The Speed of Humans (by Alan Walker in Current Anthropology, $14) 
  2. Ankles of the australopithecines, (Blog of John Hawkes, Prof. Anthropology, UW, Madison)