The Language Instinct: How the Mind Creates Language (51 page)

Obviously she was well on her way to learning English as successfully as anyone else; the tender age at which she began made all the difference.

With unsuccessful learners like Genie, there is always a suspicion that the sensory deprivation and emotional scars sustained during the horrific confinement somehow interfered with their ability to learn. But recently a striking case of first language acquisition in a normal adult has surfaced. “Chelsea” was born deaf in a remote town in northern California. A series of inept doctors and clinicians diagnosed her as retarded to emotionally disturbed without recognizing her deafness (a common fate for many deaf children in the past). She grew up shy, dependent, and languageless but otherwise emotionally and neurologically normal, sheltered by a loving family who never believed she was retarded. At the age of thirty-one she was referred to an astonished neurologist, who had her fitted with hearing aids that improved her hearing to near-normal levels. Intensive therapy by a rehabilitative team has brought her to a point where she scores at a ten-year-old level on intelligence tests, knows two thousand words, holds a job in a veterinarian’s office, reads, writes, communicates, and has become social and independent. She has only one problem, which becomes apparent as soon as she opens her mouth:

Despite intensive training and impressive gains in other spheres, Chelsea’s syntax is bizarre.

In sum, acquisition of a normal language is guaranteed for children up to the age of six, is steadily compromised from then until shortly after puberty, and is rare thereafter. Maturational changes in the brain, such as the decline in metabolic rate and number of neurons during the early school-age years, and the bottoming out of the number of synapses and metabolic rate around puberty, are plausible causes. We do know that the language-learning circuitry of the brain is more plastic in childhood; children learn or recover language when the left hemisphere of the brain is damaged or even surgically removed (though not quite at normal levels), but comparable damage in an adult usually leads to permanent aphasia.

“Critical periods” for specific kinds of learning are common in the animal kingdom. There are windows in development in which ducklings learn to follow large moving objects, kittens’ visual neurons become tuned to vertical, horizontal, and oblique lines, and white-crowned sparrows duplicate their fathers’ songs. But why should learning ever decline and fall? Why throw away such a useful skill?

Critical periods seem paradoxical, but only because most of us have an incorrect understanding of the biology of organisms’ life histories. We tend to think that genes are like the blueprints in a factory and organisms are like the appliances that the factory turns out. Our picture is that during gestation, when the organism is built, it is permanently fitted with the parts it will carry throughout its lifetime. Children and teenagers and adults and old people have arms and legs and a heart because arms and legs and a heart were part of the infant’s factory-installed equipment. When a part vanishes for no reason, we are puzzled.

But now try to think of the life cycle in a different way. Imagine that what the genes control is not a factory sending appliances into the world, but a machine shop in a thrifty theater company to which props and sets and materials periodically return to be dismantled and reassembled for the next production. At any point, different contraptions can come out of the shop, depending on current need. The most obvious biological illustration is metamorphosis. In insects, the genes build an eating machine, let it grow, build a container around it, dissolve it into a puddle of nutrients, and recycle them into a breeding machine. Even in humans, the sucking reflex disappears, teeth erupt twice, and a suite of secondary sexual characteristics emerge in a maturational schedule. Now complete the mental backflip. Think of metamorphosis and maturational emergence not as the exception but as the rule. The genes, shaped by natural selection, control bodies throughout the life span; designs hang around during the times of life that they are useful, not before or after. The reason that we have arms at age sixty is not because they have stuck around since birth, but because arms are as useful to a sixty-year-old as they were to a baby.

This inversion (an exaggeration, but a useful one) flips the critical-period question with it. The question is no longer “Why does a learning ability disappear?” but “When is the learning ability needed?” We have already noted that the answer might be “As early as possible,” to allow the benefits of language to be enjoyed for as much of life as possible. Now note that learning a language—as opposed to
using
a language—is perfectly useful as a one-shot skill. Once the details of the local language have been acquired from the surrounding adults, any further ability to learn (aside from vocabulary) is superfluous. It is like borrowing a floppy disk drive to load a new computer with the software you will need, or borrowing a turntable to copy your old collection of LP’s onto tape; once you are done, the machines can be returned. So language-acquisition circuitry is not needed once it has been used; it should be dismantled if keeping it around incurs any costs. And it probably does incur costs. Metabolically, the brain is a pig. It consumes a fifth of the body’s oxygen and similarly large portions of its calories and phospholipids. Greedy neural tissue lying around beyond its point of usefulness is a good candidate for the recycling bin. James Hurford, the world’s only computational evolutionary linguist, has put these kinds of assumptions into a computer simulation of evolving humans, and finds that a critical period for language acquisition centered in early childhood is the inevitable outcome.

Even if there is some utility to our learning a second language as adults, the critical period for language acquisition may have evolved as part of a larger fact of life: the increasing feebleness and vulnerability with advancing age that biologists call “senescence.” Common sense says that the body, like all machines, must wear out with use, but this is another misleading implication of the appliance metaphor. Organisms are self-replenishing, self-repairing systems, and there is no physical reason why we should not be biologically immortal, as in fact lineages of cancer cells used in laboratory research are. That would not mean that we would
actually
be immortal. Every day there is a certain probability that we will fall off a cliff, catch a virulent disease, be struck by lightning, or be murdered by a rival, and sooner or later one of those lightning bolts or bullets will have our name on it. The question is, is every day a lottery in which the odds of drawing a fatal ticket are the same, or do the odds get worse and worse the longer we play? Senescence is the bad news that the odds do change; elderly people are killed by falls and flus that their grandchildren easily survive. A major question in modern evolutionary biology is why this should be true, given that selection operates at every point of an organism’s life history. Why aren’t we built to be equally hale and hearty every day of our lives, so that we can pump out copies of ourselves indefinitely?

The solution, from George Williams and P. B. Medawar, is ingenious. As natural selection designed organisms, it must have been faced with countless choices among features that involved different tradeoffs of costs and benefits at different ages. Some materials might be strong and light but wear out quickly, whereas others might be heavier but more durable. Some biochemical processes might deliver excellent products but leave a legacy of accumulating pollution within the body. There might be a metabolically expensive cellular repair mechanism that comes in most useful late in life when wear and tear have accumulated. What does natural selection do when faced with these tradeoffs? In general, it will favor an option with benefits to the young organism and costs to the old one over an option with the same average benefit spread out evenly over the life span. This asymmetry is rooted in the inherent asymmetry of death. If a lightning bolt kills a forty-year-old, there will be no fifty-year-old or sixty-year-old to worry about, but there will have been a twenty-year-old and a thirty-year-old. Any bodily feature designed for the benefit of the potential over-forty incarnations, at the expense of the under-forty incarnations, will have gone to waste. And the logic is the same for unforeseeable death at any age: the brute mathematical fact is that all things being equal, there is a better chance of being a young person than being an old person. So genes that strengthen young organisms at the expense of old organisms have the odds in their favor and will tend to accumulate over evolutionary timespans, whatever the bodily system, and the result is overall senescence.

Thus language acquisition might be like other biological functions. The linguistic clumsiness of tourists and students might be the price we pay for the linguistic genius we displayed as babies, just as the decrepitude of age is the price we pay for the vigor of youth.

“
Ability to Learn Grammar Laid to Gene by Researcher.” This 1992
headline appeared not in a supermarket tabloid but in an Associated Press news story, based on a report at the annual meeting of the principal scientific association in the United States. The report had summarized evidence that Specific Language Impairment runs in families, focusing on the British family we met in Chapter 2 in which the inheritance pattern is particularly clear. The syndicated columnists James J. Kilpatrick and Erma Bombeck were incredulous. Kilpatrick’s column began:

BETTER GRAMMAR THROUGH GENETICS

Bombeck wrote:

POOR GRAMMAR? IT ARE IN THE GENES

The syndicated columns, third-hand newspaper stories, editorial cartoons, and radio shows following the symposium gave me a quick education about how scientific discoveries get addled by journalists working under deadline pressure. To set the record straight: the discovery of the family with the inherited language disorder belongs to Gopnik; the reporter who generously shared the credit with me was confused by the fact that I chaired the session and thus introduced Gopnik to the audience. No grammar gene was identified; a defective gene was inferred, from the way the syndrome runs in the family. A single gene is thought to
disrupt
grammar, but that does not mean a single gene
controls
grammar. (Removing the distributor wire prevents a car from moving, but that does not mean a car is controlled by its distributor wire.) And of course, what is disrupted is the ability to converse normally in everyday English, not the ability to learn the standard written dialect in school.

But even when they know the facts, many people share the columnists’ incredulity. Could there really be a gene tied to something as specific as grammar? The very idea is an assault on the deeply rooted belief that the brain is a general-purpose learning device, void and without form prior to experience of the surrounding culture. And if there are grammar genes, what do they do? Build the grammar organ, presumably—a metaphor, from Chomsky, that many find just as preposterous.

But if there is a language instinct, it has to be embodied somewhere in the brain, and those brain circuits must have been prepared for their role by the genes that built them. What kind of evidence could show that there are genes that build parts of brains that control grammar? The ever-expanding toolkit of the geneticist and neurobiologist is mostly useless. Most people do not want their brains impaled by electrodes, injected with chemicals, rearranged by surgery, or removed for slicing and staining. (As Woody Allen said, “The brain is my second-favorite organ.”) So the biology of language remains poorly understood. But accidents of nature and ingenious indirect techniques have allowed neurolinguists to learn a surprising amount. Let’s try to home in on the putative grammar gene, beginning with a bird’s-eye view of the brain and zooming in on smaller and smaller components.

We can narrow down our search at the outset by throwing away half the brain. In 1861 the French physician Paul Broca dissected the brain of an aphasic patient who had been nicknamed “Tan” by hospital workers because that was the only syllable he uttered. Broca discovered a large cyst producing a lesion in Tan’s left hemisphere. The next eight cases of aphasia he observed also had left-hemisphere lesions, too many to be attributed to chance. Broca concluded that “the faculty for articulate language” resides in the left hemisphere.

In the 130 years since, Broca’s conclusion has been confirmed by many kinds of evidence. Some of it comes from the convenient fact that the right half of the body and of perceptual space is controlled by the left hemisphere of the brain and vice versa. Many people with aphasia suffer weakness or paralysis on the right side, including Tan and the recovered aphasic of Chapter 2, who awoke thinking that he had slept on his right arm. The link is summed up in Psalms 137:5–6:

Normal people recognize words more accurately when the words are flashed to the right side of their visual field than when they are flashed to the left, even when the language is Hebrew, which is written from right to left. When different words are presented simultaneously to the two ears, the person can make out the word coming into the right ear better. In some cases of otherwise incurable epilepsy, surgeons disconnect the two cerebral hemispheres by cutting the bundle of fibers running between them. After surgery the patients live completely normal lives, except for a subtlety discovered by the neuroscientist Michael Gazzaniga: when the patients are kept still, they can describe events taking place in their right visual field and can name objects in their right hand, but cannot describe events taking place in their left visual field or name objects placed in their left hand (though the right hemisphere can display its awareness of those events by nonverbal means like gesturing and pointing). The left half of their world has been disconnected from their language center.

When neuroscientists look directly at the brain, using a variety of techniques, they can actually see language in action in the left hemisphere. The anatomy of the normal brain—its bulges and creases—is slightly asymmetrical. In some of the regions associated with language, the differences are large enough to be seen with the naked eye. Computerized Axial Tomography (CT or CAT) and Magnetic Resonance Imaging (MRI) use a computer algorithm to reconstruct a picture of the living brain in cross-section. Aphasics’ brains almost always show lesions in the left hemisphere. Neurologists can temporarily paralyze one hemisphere by injecting sodium amytal into the carotid artery. A patient with a sleeping right hemisphere can talk; a patient with a sleeping left hemisphere cannot. During brain surgery, patients can remain conscious under local anesthetic because the brain has no pain receptors. The neurosurgeon Wilder Penfield found that small electric shocks to certain parts of the left hemisphere could silence the patient in mid-sentence. (Neurosurgeons do these manipulations not out of curiosity but to be sure that they are not cutting out vital parts of the brain along with the diseased ones.) In a technique used on normal research subjects, electrodes are pasted all over the scalp, and the subjects’ electroencephalograms (EEG’s) are recorded as they read or hear words. There are recognizable jumps in the electrical signal that are synchronized with each word, and they are more prominent in the electrodes pasted on the left side of the skull than in those on the right (though this finding is tricky to interpret, because an electrical signal generated deep in one part of the brain can radiate out of another part).

In a new technique called Positron Emission Tomography (PET), a volunteer is injected with mildly radioactive glucose or water, or inhales a radioactive gas, comparable in dosage to a chest X-ray, and puts his head inside a ring of gamma-ray detectors. The parts of the brain that are more active burn more glucose and have more oxygenated blood sent their way. Computer algorithms can reconstruct which parts of the brain are working harder from the pattern of radiation that emanates from the head. An actual picture of metabolic activity within a slice of the brain can be displayed in a computer-generated photograph, with the more active areas showing up in bright reds and yellows, the quiet areas in dark indigos. By subtracting an image of the brain when its owner is watching meaningless patterns or listening to meaningless sounds from an image when the owner is understanding words or speech, one can see which areas of the brain “light up” during language processing. The hot spots, as expected, are on the left side.

What exactly is engaging the left hemisphere? It is not merely speechlike sounds, or wordlike shapes, or movements of the mouth, but abstract
language
. Most aphasic people—Mr. Ford from Chapter 2, for example—can blow out candles and suck on straws, but their writing suffers as much as their speech; this shows that it is not mouth control but language control that is damaged. Some aphasics remain fine singers, and many are superb at swearing. In perception, it has long been known that tones are discriminated better when they are played to the left ear, which is connected most strongly to the right hemisphere. But this is only true if the tones are perceived as musical sounds like hums; when the ears are Chinese or Thai and the same tones are features of phonemes, the advantage is to the right ear and the left hemisphere it feeds.

If a person is asked to shadow someone else’s speech (repeat it as the talker is talking) and, simultaneously, to tap a finger to the right or the left hand, the person has a harder time tapping with the right finger than with the left, because the right finger competes with language for the resources of the left hemisphere. Remarkably, the psychologist Ursula Bellugi and her colleagues have shown that the same thing happens when deaf people shadow one-handed signs in American Sign Language: they find it harder to tap with their right finger than with their left finger. The gestures must be tying up the left hemispheres, but it is not because they are gestures; it is because they are
linguistic
gestures. When a person (either a signer or a speaker) has to shadow a goodbye wave, a thumbs-up sign, or a meaningless gesticulation, the fingers of the right hand and the left hand are slowed down equally.

The study of aphasia in the deaf leads to a similar conclusion. Deaf signers with damage to their left hemispheres suffer from forms of sign aphasia that are virtually identical to the aphasia of hearing victims with similar lesions. For example, Mr. Ford’s sign-language counterparts are unimpaired at nonlinguistic tasks that place similar demands on the eyes and hands, such as gesturing, pantomiming, recognizing faces, and copying designs. Injuries to the right hemisphere of deaf signers produce the opposite pattern: they remain flawless at signing but have difficulty performing visuospatial tasks, just like hearing patients with injured right hemispheres. It is a fascinating discovery. The right hemisphere is known to specialize in visuospatial abilities, so one might have expected that sign language, which depends on visuospatial abilities, would be computed in the right hemisphere. Bellugi’s findings show that language, whether by ear and mouth or by eye and hand, is controlled by the left hemisphere. The left hemisphere must be handling the abstract rules and trees underlying language, the grammar and the dictionary and the anatomy of words, and not merely the sounds and the mouthings at the surface.

Why is language so lopsided? A better question is, why is the rest of a person so symmetrical? Symmetry is an inherently improbable arrangement of matter. If you were to fill in the squares of an 8 × 8 checkerboard at random, the odds are less than one in a billion that the pattern would be bilaterally symmetrical. The molecules of life are asymmetrical, as are most plants and many animals. Making a body bilaterally symmetrical is difficult and expensive. Symmetry is so demanding that among animals with a symmetrical design, any disease or weakness can disrupt it. As a result, organisms from scorpion flies to barn swallows to human beings find symmetry sexy (a sign of a fit potential mate) and gross asymmetry a sign of deformity. There must be something in an animal’s lifestyle that makes a symmetrical design worth its price. The crucial lifestyle feature is mobility: the species with bilaterally symmetrical body plans are the ones that are designed to move in straight lines. The reasons are obvious. A creature with an asymmetrical body would veer off in circles, and a creature with asymmetrical sense organs would eccentrically monitor one side of its body even though equally interesting things can happen on either side. Though locomoting organisms are symmetrical side-to-side, they are not (apart from Dr. Dolittle’s Push-mi-pull-you) symmetrical front-and-back. Thrusters apply force best in one direction, so it is easier to build a vehicle that can move in one direction and turn than a vehicle that can move equally well in forward and reverse (or that can scoot off in any direction at all, like a flying saucer). Organisms are not symmetrical up-and-down because gravity makes up different from down.