The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

One reason for thinking that Broca’s area is specialized exclusively for syntactic structure is the observation that it seems to have a life of its own, quite independent of the meaning conveyed. It’s almost as though this patch of cortex has an autonomous set of grammatical rules that are intrinsic to its networks. Some of them seem quite arbitrary and apparently nonfunctional, which is the main reason linguists assert its independence from semantics and meaning and dislike thinking of it as having evolved from anything else in the brain. The extreme view is exemplified by Chomsky, who believes that it didn’t even evolve through natural selection!

The brain region concerned with semantics is located in the left temporal lobe near the back of the great horizontal cleft in the middle of the brain (see Figure 6.1). This region, called Wernicke’s area, appears to be specialized for the representation of meaning. Dr. Hamdi’s Wernicke’s area was obviously intact. He could still comprehend what was said to him and could convey some semblance of meaning in his conversations. Conversely, Wernicke’s aphasia—what you get if your Wernicke’s area is damaged but your Broca’s area remains intact—is in a sense the mirror image of Broca’s aphasia: The patient can fluently generate elaborate, smoothly articulated, grammatically flawless sentences, but it’s all meaningless gibberish. At least that’s the official party line, but later I’ll provide evidence that this isn’t entirely true.

THESE BASIC FACTS about the major language-related brain areas have been known for more than a century. But many questions remain. How complete is the specialization? How does the neural circuitry within each area actually do its job? How autonomous are these areas, and how do they interact to generate smoothly articulated, meaningful sentences? How does language interact with thought? Does language enable us to think, or does thinking enable us to talk? Can we think in a sophisticated manner without silent internal speech? And lastly, how did this extraordinarily complex, multicomponent system originally come into existence in our hominin ancestors?

This last question is the most vexing. Our journey into full-blown humanity began with nothing but the primitive growls, grunts, and groans available to our primate cousins. By 75,000 to 150,000 years ago, the human brain was brimming with complex thoughts and linguistic skills. How did this happen? Clearly, there must have been a transitional phase, yet it’s hard to imagine how linguistic brain structures of intermediate complexity might have worked, or what functions they might have served along the way. The transitional phase must have been at least partially functional; otherwise it couldn’t have been selected for, nor served as an evolutionary bridge for the eventual emergence of more sophisticated language functions.

To understand what this bridge might have been is the main purpose of this chapter. I should point out that by “language” I don’t mean just “communication.” We often use the two words interchangeably, but in fact they are very different. Consider the vervet monkey. Vervets have three alarm calls to alert each other about predators. The call for leopard prompts the troupe to bolt for the nearest trees. The call for serpent causes the monkeys to stand up on two legs and peer down into the grass. And when vervets hear the eagle call, they look up into the air and seek shelter in the underbrush. It’s tempting to conclude that these calls are like words, or at least the precursors to words, and that the monkey does have a primitive vocabulary of sorts. But do the monkeys really know there’s a leopard, or do they just rush for the nearest tree reflexively when an alarm call is sounded? Or perhaps the call really just means “climb” or “there’s danger on the ground,” rather than the much richer concept of leopard that a human brain harbors. This example tells us that mere communication isn’t language. Like an air-raid siren or a fire alarm, vervets’ cries are generalized alerts that refer to specific situations; they are almost nothing like words.

In fact, we can list a set of five characteristics that make human language unique and radically different from other types of communication we see in vervets or dolphins:

1. Our vocabulary (lexicon) is enormous. By the time a child is eight years old, she has almost six hundred words at her disposal—a figure that vastly exceeds the nearest runner-up, the vervet monkey, by two orders of magnitude. One could argue, though, that this is really a matter of degree than a qualitative jump; maybe we just have much better memories.