Kluge: The Haphazard Construction of the Human Mind (Houghton Mifflin; 2008)

Consider first the very sounds of language. It's probably no accident that language evolved primarily as a medium of sound, rather than, say, vision or smell. Sound travels over reasonably long distances, and it allows one to communicate in the dark, even with others one can't see. Although much the same might be said for smell, we can modulate sound much more rapidly and precisely, faster than even the most sophisticated skunk can modulate odor. Speech is also faster than communicating by way of physical motion; it can flow at about twice the speed of sign language.

Still, if I were building a system for vocal communication from scratch, I'd start with an iPod: a digital system that could play back any sound equally well. Nature, in contrast, started with a breathing tube. Turning that breathing tube into a means of vocal production was no small feat. Breathing produces air, but sound is modulated air, vibrations produced at just the right sets of frequencies. The Rube Goldberg-like vocal system consists of three fundamental parts: respiration, phonation, and articulation.

Respiration is just what it sounds like. You breathe in, your chest expands; your chest compresses, and a stream of air comes out. That stream of air is then rapidly divided by the vocal folds into smaller puffs of air (phonation), about 80 times a second for a baritone like James Earl Jones, as much as 500 times per second for a small child. From there, this more-or-less constant sound source is filtered, so that only a subset of its many frequencies makes it through. For those who like visual analogies, imagine producing a perfect white light and then applying a filter, so that only part of the spectrum shines through. The vocal tract works on a similar "source and filter" principle. The lips, the tip of the tongue, the tongue body, the velum (also known as the soft palate), and the glottis (the opening between the vocal folds) are known collectively as articulators. By varying their motions, these articulators shape the raw sound stream into what we know as speech: you vibrate your vocal cords when you say "bah"but not "pah"; you close your lips when say "mah" but move your tongue to your teeth when you say "nah."

Respiration, phonation, and articulation are not unique to humans. Since fish walked the land, virtually all vertebrates, from frogs to birds to mammals, have used vocally produced sound to communicate. Human evolution, however, depended on two key enhancements: the lowering of our larynx (not unique to humans but very rare elsewhere in the animal kingdom) and increased control of the ensemble of articulators that shape the sound of speech. Both have consequences.

Consider first the larynx. In most species, the larynx consists of a single long tube. At some point in evolution, our larynx dropped down. Moreover, as we changed posture and stood upright, it took a 90-degree turn, dividing into two tubes of more or less equal length, which endowed us with considerably more control of our vocalizations — and radically increased our risk of choking. As first noted by Darwin, "Every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs" — something we're all vulnerable to.*

Maybe you think the mildly increased risk of choking is a small price to pay, maybe you don't. It certainly didn't have to be that way; breathing and talking could have relied on different systems. Instead, our propensity for choking is one more clear sign that evolution tinkered with what was already in place. The result is a breathing tube that does double duty as a vocal tract — in occasionally fatal fashion.

In any event, the descended larynx was only half the battle. The real entrיe into speech came from significantly increased control over our articulators. But here too the system is a bit of a kluge. For one thing, the vocal tract lacks the elegance of the iPod, which can play back more or less any sound equally well, from Moby's guitars and flutes to hip-hop's car crashes and gunshots. The vocal tract, in contrast, is tuned only to words. All the world's languages are drawn from an inventory of 90 sounds, and any particular language employs no more than half that number — an absurdly tiny subset when you think of the many distinct sounds the ear can recognize.

Imagine, for example, a human language that would refer to something by reproducing the sound it makes. I'd refer to my favorite canine, Ari, by reproducing his woof, not by calling him a dog. But the three-part contraption of respiration, phonation, and articula