Just as there is a nonarbitrary correspondence and cross-activation between brain maps for sights and sounds (the bouba-kiki effect), perhaps there is a similar correspondence—a built-in translation—between visual and auditory maps, on the one hand, and the motor maps in Broca’s area on the other. If this sounds a bit cryptic, think again of words like “teeny-weeny,” “un peau,” and “diminutive,” for which the mouth and lips and pharynx actually become small as if to echo or mime the visual smallness, whereas words like “enormous” and “large” entail an actual physical enlargement of the mouth. A less obvious example is “fudge,” “trudge,” “sludge,” “smudge,” and so on, in which there is a prolonged tongue pressing on the palate before the sudden release, as if to mimic the prolonged sticking of the shoe in mud before the relatively sudden release. Here, yet again, is a built-in abstraction device that translates visual and auditory contours into vocal contours specified by muscle twitches.
Another less obvious piece of the puzzle is the link between manual gestures and lip and tongue movements. As mentioned in Chapter 4, Darwin noticed that when you cut with a pair of scissors, you may unconsciously echo these movements by clenching and unclenching your jaws. Since the cortical areas concerned with the mouth and hand are right next to each other, perhaps there is an actual spillover of signals from hands to mouth. As in synesthesia, there appears to be a built-in cross-activation between brain maps, except here it is between two motor maps rather than between sensory maps. We need a new name for this, so let’s call it “synkinesia” (syn meaning “together,” kinesia meaning “movement”).
Synkinesia may have played a pivotal role in transforming an earlier gestural language (or protolanguage, if you prefer) of the hands into spoken language. We know that emotional growls and shrieks in primates arise mainly in the right hemisphere, especially from a part of the limbic system (the emotional core of the brain) called the anterior cingulate. If a manual gesture were being echoed by orofacial movements while the creature was simultaneously making emotional utterances, the net result would be what we call words. In short, ancient hominins had a built-in, preexisting mechanism for spontaneously translating gestures into words. This makes it easier to see how a primitive gestural language could have evolved into speech—an idea that many classical psycholinguists find unappealing.
As a concrete example, consider the phrase “come hither.” Notice that you gesture this idea by holding your palm up and flexing your fingers toward yourself as if to touch the lower part of the palm. Amazingly, your tongue makes a very similar movement as it curls back to touch the palate to utter “hither” or “here”—examples of synkinesia. “Go” involves pouting the lips outward, whereas “come” involves drawing the lips together inward. (In the Indian Dravidian language Tamil—unrelated to English—the word for go is “po”).
Obviously, whatever the original language was back in the Stone Age, it has since been embellished and transformed countless times beyond reckoning, so that today we have languages as diverse as English, Japanese, !Kung, and Cherokee. Language, after all, evolves with incredible rapidity; sometimes just two hundred years is enough to alter a language to the point where a young speaker would be barely able to communicate with her great-great-grandmother. By this token, once the juggernaut of full linguistic competence arose in the human mind and culture, the original synkinetic correspondences were probably lost or blended beyond recognition. But in my account, synkinesia sowed the initial seeds of lexicon, helping to form the original vocabulary base on which subsequent linguistic elaboration was built.
Synkinesia and other allied attributes, such as mimicry of other people’s movements and extraction of commonalities between vision and hearing (bouba-kiki), may all rely on computations analogous to what mirror neurons are supposed to do: link concepts across brain maps. These sorts of linkages remind us again of their potential role in the evolution of protolanguage. This hypothesis may seem speculative to orthodox cognitive psychologists, but it provides a window of opportunity—indeed, the only one we have to date—for exploring the actual neural mechanisms of language. And that’s a big step forward. We will pick up the threads of this argument later in this chapter.
We also need to ask how gesturing evolved in the first place.2 At least for verbs like “come” or “go,” it may have emerged through the ritualization of movements that were once used for performing those actions. For instance, you may actually pull someone toward you by flexing your fingers and elbow toward you while grabbing the person. So the movement itself (even if divorced from the actual physical object) became a means of communicating intent. The result is a gesture. You can see how the same argument applies to “push,” “eat,” “throw,” and other basic verbs. And once you have a vocabulary of gestures in place, it becomes easier for corresponding vocalizations to evolve, given the preexisting hardwired translation produced by synkinesia. (The ritualization and reading of gestures may, in turn, have involved mirror neurons, as alluded to in previous chapters.)
So we now have three types of map-to-map resonance going on in the early hominin brain: visual-auditory mapping (bouba-kiki); mapping between auditory and visual sensory maps, and motor vocalization maps in Broca’s area; and mapping between Broca’s area and motor areas controlling manual gestures. Bear in mind that each of these biases was probably very small, but acting in conjunction they could have progressively bootstrapped each other, creating the snowball effect that culminated in modern language.
IS THERE ANY neurological evidence for the ideas discussed so far? Recall that many neurons in a monkey’s frontal lobe (in the same region that appears to have become Broca’s area in us) fire when the animal performs a highly specific action like reaching for a peanut, and that a subset of these neurons also fires when the monkey watches another monkey grab a peanut. To do this, the neuron (by which I really mean “the network of which the neuron is a part”) has to compute the abstract similarity between the command signals specifying muscle contraction sequences and the visual appearance of peanut reaching seen from the other monkey’s vantage point. So the neuron is effectively reading the other individual’s intention and could, in theory, also understand a ritualized gesture that resembles the real action. It struck me that the bouba-kiki effect provides an effective bridge between these mirror neurons and ideas about synesthetic bootstrapping I have presented so far. I considered this argument briefly in an earlier chapter, let me elaborate the argument now to make the case for its relevance to the evolution of protolanguage.
The bouba-kiki effect requires a built-in translation between visual appearance, sound representation in the auditory cortex, and sequences of muscle twitches in Broca’s area. Performing this translation almost certainly involves the activation of circuits with mirror-neuron-like properties, mapping one dimension onto another. The inferior parietal lobule (IPL), rich in mirror neurons, is ideally suited for this role. Perhaps the IPL serves as a facilitator for all such types of abstraction. I emphasize, again, that these three features (visual shape, sound inflections, and lip and tongue contour) have absolutely nothing in common except the abstract property of, say, jaggedness or roundness. So what we are seeing here is the rudiments—and perhaps relics of the origins—of the process called abstraction that we humans excel at, namely, the ability to extract the common denominator between entities that are otherwise utterly dissimilar. From being able to extract the jaggedness of the broken glass shape and the sound kiki to seeing the “fiveness” of five pigs, five donkeys, or five chirps may have been a short step in evolution but a giant step for humankind.