Walking Back

Sometimes what you are is what you aren’t; thus, Plato famously defined man as a featherless biped. But Aristotle was the one who first put serious effort into understanding bipeds. In Part 4 of his On the Gait of Animals, he considered the question of why animals had tops & bottoms, fronts & backs, lefts & rights. He related them to activities. Top/bottom comes from eating – you eat with the top part and excrete with the bottom. (Plants, he noted, are upside down, in that they eat with the bottom.) Front/back comes from sensing – you have your sense organs on the front. Left/right comes from motion – whether you walk or slither, you always have to push off with one side and move the other.

Aristotle must have been right-handed, though. Consider:

That the beginning of movement is on the right is indicated by the fact that all men carry burdens on the left shoulder; in this way they set free the side which initiates movement and enable the side which bears the weight to be moved. And so men hop easier on the left leg; for the nature of the right is to initiate movement, that of the left to be moved.

And later:

As all animals then start movement from the right, and the right moves in the same direction as the whole, it is necessary for all to be alike right-handed. And man has the left limbs detached more than any other animal because he is natural in a higher degree than the other animals; now the right is naturally both better than the left and separate from it, and so in man the right is more especially the right, more dextrous that is, than in other animals.

He also says that you can tell a biped by whether the top and the front are or are not identically situated. Thus, a bird is a biped, but an octopus isn’t. Or at least isn’t most of the time, as this video from UC Berkeley will attest. In a paper published in the March 25 issue of Science, Crissy Huffard and Robert Full reported that the Indonesian coconut octopus will occasionally wrap 6 of its arms around its body and lope ahead on the remaining two, at speeds as fast as 400 m per hour. (Science is a subscription journal, but there’s a lengthy Berkeley press release that’s free.) Apparently, walking this way preserves the camouflage illusion that would have to be shed if the octopus were to go into traditional jet mode. The unanswered question: Is the octopus right-tentacled or left-tentacled?

If walking invertebrates threaten your Aristotelian nature, then avoid skin diving. One of the rare (but common enough for pictures) pleasures of reef diving is catching a crinoid on walkabout. Crinoids look more like flowers than animals, but they are among the few of our most ancient ancestors that persist in modern seas. (They even made it through the Permian extinction.) They are usually quite slow, but a report in an issue of Science News last month includes a video of a crinoid off Grand Bahama Island that is racing along at 140 m per hour. Chasing an octopus, no doubt. (Science News is also a subscription journal; here’s the press release from the Geological Society of America.) Clearly, the crinoid is a biped without Aristotelian asymmetry.