Steve Kass

There is still no good answer to the question “Why can’t we walk straight?”, observed Robert Krulwich’s recorded voice at a recent live taping for Radiolab at The Greene Space. Robert’s observation ressounded¹ today on the “NPR sciencey blog” Krulwich Wonders.

For 80 years, scientists have been trying to explain this tendency to turn when you think you are going straight. … Try as they might, and they’re still trying these experiments, nobody has figured out why we can’t go straight.

When I was a kid, Someone thought they’d figured it out. One’s dominant leg took longer strides, They taught me. I also learned, or maybe inferred, that I should find a leftie to walk with me should I ever need to cross a desert in the fog, at night, or while blindfolded.

But hearing Robert talk about this twice in as many weeks, I realized that They’d been wrong, and that crossing a desert in the fog was not a challenge I’d be ready to meet. (Also, I only then realized that a leftie might not be handy when the challenge arose, anyway.)

Ignoring my sudden and deepening nonplus, I focused on the question. Analogy time.² Robert’s headlineworthy version of the question is an oversimplification of the quandary, but I’ll notwithstand that fact for now.

Why can’t we fly? (Some animals can.) Because we don’t have small bodies, hollow bones, and wings (like some flying-capable animals do); nor do we have really tiny invertebrate bodies and wings (like some other flying-capable animals do).

Why can’t we hear high-pitched sounds? (Some animals can.) Because human ears (unlike the ears of the animals that can) aren’t physically able to convert high-pitched sounds into nerve impulses.

So why can’t we maintain our direction over long distances without a visual point of reference? (Some animals, especially flying-capable ones, can.) Because (unlike those animals) humans never underwent any evolutionary pressure to develop a mechanism to do so?

Robert mentioned one of the trying scientists by name: Jan Sousman. Jan’s article, Walking Straight into Circles, recently appeared in the journal Current Biology (a cornucopia of articles at the titles of which biologists surely titter: Olfaction: When Nostrils Compete; Metastasis: Alone or Together?; Addiction: Flies Hit the Skids; Flagella and Cilia: The Long and the Short of It; and Melanocyte Production: Dark Side of the Schwann Cell).

Jan and his coauthors wrote a wonderful paper. Among many beautiful sentences and figures, they report that their subjects’ “walking trajectories show exactly the kind of behavior that would be expected if the subjective sense of straight ahead were to follow a correlated random walk.” They also mention J. R. R. Tolkien’s The Lord of the Rings: The Two Towers to point out that the belief “that people who get lost end up walking in circles is widespread.”

So “because we can’t” isn’t really such a good answer. Our proprioception (that sixth sense that allows us to touch our noses in the dark when we haven’t had too much to drink) does provide a subjective sense of straight ahead. However, it isn’t very reliable for very far or for very long.`

¹ I initially wrote reappeared, which on rereading, sounded (or more sensibly, looked) wrong, because Robert’s voice never appeared (as in became visible to the eye) in the first place. Unable to solve the Miller Analogy SEE : REAPPEAR :: HEAR: with an existing word, I had to invent the perfect answer: res̈ound (which should appear as the word resound with an umlaut/trema/diaeresis over the s). This answer is in fact all the more perfect (not to mention very unique) for having been invented by a “greater New Yorker.” Unfortunately, as much as I like the idea of using ¨ to estop a preceding prefix from losing its strict meaning, it fails in practical terms. Very few consonants appear in Unicode preëquipped with the dots, and Unicode’s zero-width combining diaeresis, the solution in theory, is unworkably fussy.

² Yay!