The Glory of Being a Biped

Body geometry matters for function and consciousness, by Bill Softky

If you think about it, we bipeds have the most symmetric and supple body-form in 500 million years.

Way back then, the first sea-snakes won the game on the first try. A snake-spine is on the one hand an incredibly simple shape — head at one end, tail the other, wiggly stick in between — but it can create an infinitude of shapes and motions. Aside from the ribcage (for breathing), that shape has perfect cylindrical symmetry. The metabolic systems line up along the spine according to how far their input has to travel to the brain, with high-bandwidth tasks like vision, navigation, and food-acquisition at one end, and low-bandwidth ones like digestion, elimination and reproduction at the other. Kind of like the “chakras,” but it’s not just a yoga architecture, it’s a vertebrate architecture.

To gloss over whole disciplines and lineages of anatomy and taxonomy with a grand simplification only a theoretical physicist would love, here’s what happened next. First, on top of that basic spine-shape, you add fins. OK, that requires some kind of hips or shoulders, or maybe both, but the spine is still there in the middle, doing the work, the computations, and the strategy. Then add more joints to those fins, maybe even “fingers,” but the basic layout stays the same, like a fish. And as long as it stays in the ocean, it has the full freedom of 3-D navigation, the most flexible foraging or flight possible.

No longer true on land. In the famous evolutionary image of a fish walking on its flippers, two big things have changed. First, on flat land, navigation is 2D, which is a geometric insult to a system evolved for 3-D operation. More crucially, gravity is now tugging sideways on the spine (a further geometric insult), and the spine is supported against it at two specific locations, the hips and shoulders, instead of floating free like in the ocean.

So poor old quadrupeds, even since lizards and dinosaurs, have endured lives with the breathtaking symmetry of their interior spinal architectures horribly hobbled by asymmetric support against gravity. Yes, they did get along just fine, and reproduced and led to us and all that, but still, all four of their limbs were dedicated full-time just to holding them up, and their necks, abdomens, and backs needed to differentiate end-to-end and front-to-back. No more simple architecture; life was geometrically complicated and mechanically inefficient.

Fast-forward through monkeys and primates, who by hanging their spines from one end pulled them out straight again. After that, just a few million years ago, came us bipeds, a few steps (literally) beyond bonobos. Bipeds, presumably for reasons of immediate physical pleasure, decided to spend all day upright, balanced on two feet instead of four. Geometrically, that changed everything.

Our brains got bigger, to handle the newer, ultra-sensitive balance equations they needed to solve. The spine became truly upright, with no requirements to bend front or back, and no consistent sideways load of gravity. Not quite the 360° suppleness of sea-snakes, but way, way better than quadruped constraints, and when they climbed they really could even navigate in three dimensions. With the spine and head both upright, our heads got to spin around their natural axes again, they way they originally evolved.

Best of all, our spines finally had regained their freedom to vibrate any way they wanted, which not only gave more range of motion, but let them use a simpler and more efficient operating system and more efficient mechanical gait. So we not only got bigger brains, we got faster software and firmware.

Because gravity doesn’t tug sideways on us when walking like it does on quadrupeds or even chimps, we walk and run more efficiently, which provides advantages in persistsence-hunting — chasing prey down until they tire out. Basically, over long distances, the most inefficient animal overheats first, and our ancestors’ upright running and hairless skin made them immune from overheating. So persistence-hunting became our ancestors’ core competency, along with skilled acoustic mimicry (bird-calls and such) thanks to our supple voice-boxes.

But there was a cost. Those extra skills came from computational improvements, a process requiring huge amounts of calibration data. A biped, to keep its elaborate mechanical and vibrational mechanism well-tuned, needs to move regularly through all its range of motion, exertion, and social interaction. To hone our motor skills, we needed motor practice, every day.

Hence hard-wired prime directives for autonomous motion and vocalization, i.e. song and dance. To stay in calibration, we need to stand up straight and dance and sing. How fortunate that we enjoy it too. Or maybe Nature programmed us that way?

Standing erect brought another huge benefit: our hands no longer needed to bear weight or balance, so we could specialize them for other things. Like hand-signals. Throwing. And tool-making, and art-making, which all were so successful that now, a hundred thousand years later, the products of our hands now captivate, and sometimes physically capture, the most symmetric large animals on in the atmosphere.

So the dancing and singing our biped frames need for calibration, and which demonstrably “nurture the soul” (to use a traditional phrase), are left out in favor of sofas and TVs. That’s so not what we evolved to be.