The body, p.12
The Body, page 12
We can bite pretty hard. Bite force is measured in units called newtons (in honor of Isaac Newton’s second law of motion, not his oral ferocity), and if you are a typical adult male, you can muster about four hundred newtons of force, which is quite a lot, though nothing like as much as an orangutan, which can bite with five times as much vigor. Still, when you consider how well you can demolish, say, an ice cube (try doing that with your fists and see how far you get) and how little space the five muscles of the jaw occupy, you can appreciate that human chomping is pretty capable.
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The tongue is a muscle, but quite unlike any other. For one thing, it is exquisitely sensitive—think how adroitly you pick out something in your food that shouldn’t be there, like a tiny piece of eggshell or grain of sand—and intimately involved in vital activities like speech articulation and tasting food. When you eat, the tongue darts about like a nervous host at a cocktail party, checking the taste and shape of every morsel in preparation for dispatching it onward to the gullet. As everyone knows, the tongue is coated with taste buds. These are clumps of taste receptor cells found in the bumps on your tongue, which are formally called papillae. They come in three different shapes: circumvallate (or rounded), fungiform (mushroom shaped), and foliate (leaf shaped). They are among the most regenerative of all cells in the body and are replaced every ten days.
For years, even textbooks spoke of a tongue map, with the elemental tastes each occupying a well-defined zone: sweet on the tip of the tongue, sour at the sides, bitter at the back. In fact, that is a myth, traced to a textbook written in 1942 by one Edwin G. Boring, a Harvard psychologist who misinterpreted a paper written by a German researcher forty years before that. Altogether we have about ten thousand taste buds, mostly distributed around the tongue, except in the very middle, where there are none at all. Additional taste buds are found in the roof of the mouth and lower down the throat, which is said to be why some medicines taste bitter as they go down.
As well as the mouth, the body has taste receptors in the gut and throat (to help identify spoiled or toxic substances), but they don’t connect to the brain in the same way as the taste receptors on your tongue, and for good reason. You don’t want to taste what your stomach is tasting. Taste receptors have also been found in the heart, the lungs, and even the testicles. No one knows quite what they are doing there. They also send signals to the pancreas to adjust insulin output, and it may be connected to that.
It is generally supposed that taste receptors evolved for two deeply practical purposes: to help us find energy-rich foods (like sweet, ripe fruits) and to avoid dangerous ones. But it must also be said that they don’t always fulfill either role terribly well. Captain James Cook, the great British explorer, had a salutary demonstration of that in 1774, on his second epic voyage through the Pacific. One of his crew caught a meaty fish, which no one aboard recognized. It was cooked and proudly presented to the captain and two of his officers, but because they had already dined, they merely sampled it and had the remainder put aside for the following day. This was a very lucky thing, for in the middle of the night all three found themselves “seized with an extraordinary weakness and numbness all over our limbs.” Cook was for some hours virtually paralyzed and unable to lift anything—even a pencil. The three men were given emetics, to clear their stomachs. They were lucky to survive, for what they had sampled was puffer fish. These contain a poison called tetrodotoxin, which is a thousand times more powerful than cyanide.
Despite its extreme toxicity, puffer fish is a famous delicacy in Japan, where it is called fugu. Preparing fugu is a job entrusted to only a few specially trained chefs, who must carefully remove the fish’s liver, intestines, and skin before cooking because they are particularly saturated in poison. Even then, enough toxin remains to numb the mouth and leave the diner feeling pleasantly woozy. In one famous case in 1975, a well-known actor named Bandō Mitsugorō ate four helpings of fugu—despite pleadings to stop—and died wretchedly four hours later of asphyxiation. Fugu still kills about one person a year.
The difficulty with fugu is that by the time the ill effects become evident, it is much too late to do anything about it. The same is true of all kinds of other substances, from belladonna, or deadly nightshade, to a wide range of fungi. In 2008, in a widely publicized case, the British author Nicholas Evans and three members of his family became deathly ill on holiday in Scotland when they mistook a deadly mushroom, Cortinarius speciosissimus, for its benign and delicious cousin cèpe. The effects were horrific—Evans needed a kidney transplant, and all members of the party suffered lasting damage—yet nothing in the taste alerted anyone to the perils ahead. The fact is, our putative defenses are far more putative than defensive.
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We have about ten thousand taste receptors, but we actually have more pain and other somatosensory receptors than taste receptors in our mouths. Because they exist side by side on the tongue, we sometimes mix them up. When you describe a chili as hot, you are being more literal than you might suppose. Your brain interprets it as being actually burned. As Joshua Tewksbury of the University of Colorado has put it, “Chilies innervate the same neurons that you activate when you touch a 335-degree burner. Essentially, our brain is telling us that we have got our tongue on the stove.” In the same way, menthol is perceived as being cool even in the heated smoke of a cigarette.
The active ingredient in all chili peppers is a chemical called capsaicin. When you ingest capsaicin, the body releases endorphins—it’s not at all clear why—and that provides us with a literally warm glow of pleasure. As with any warmth, however, it can quickly grow uncomfortable and then intolerable.
The amount of heat in chilies is measured in units called Scovilles, after Wilbur Scoville (1865–1942), an unassuming American pharmacist who had no known interest in hot dishes and very possibly never tasted a genuinely spicy food in his life. Scoville spent much of his career training students at the Massachusetts College of Pharmacy and churning out academic papers with titles like “Some Observations on Glycerin Suppositories,” but in 1907 at the age of forty-two, apparently tempted by a big salary, he moved to Detroit to take up a job with a large pharmaceutical company, Parke, Davis & Co. One of his tasks there was to oversee production of a popular muscle salve called Heet. The warmth of Heet came from chili peppers—the same ones used in food—but the heat of peppers varied enormously from one delivery to another, and there was no reliable way of judging how much to put into any given batch. So Scoville came up with something called the Scoville Organoleptic Test, which was a scientific method for measuring the hotness of any pepper. It is still the standard used today.
A bell pepper will have a Scoville rating of between 50 and 100. Jalapeños usually measure in the range of 2,500 to 5,000 Scovilles. Nowadays many people breed peppers specifically to make them as hot as possible. The record holder at the time of writing is the Carolina Reaper at 2.2 million Scovilles. Capsaicin in pure form has 16 million Scovilles. A purified version of a Moroccan spurge plant—a cousin of the innocuous common garden flowering euphorbia—has been measured at 16 billion Scovilles. Such superhot peppers are of no use in foods—they are beyond any human threshold—but they are of interest to manufacturers of pepper sprays, which also use capsaicin.
Capsaicin has been reported to lower blood pressure, fight inflammation, and reduce susceptibility to cancer, among quite a lot else of benefit to the average human. In a study reported in the British Medical Journal, Chinese adults who ate a lot of capsaicin were 14 percent less likely to die, from any cause, during the period of the study compared with less adventurous eaters. But, as always with these findings, the fact that the subjects ate a lot of spicy food and were 14 percent better at surviving may only be coincidental.*2
Incidentally, we have pain detectors not only in the mouth but also in the eyes, anus, and vagina, which is why spicy foods can cause discomfort there.
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As far as taste goes, our tongue can only identify the familiar basics of sweet, salty, sour, bitter, and umami (a Japanese word meaning “savory” or “meaty”). Some authorities believe we also have taste receptors specifically allocated for metal, water, fat, and another Japanese concept called kokumi, meaning “full-bodied” or “hearty,” but the only ones that are universally accepted are the five basics.
In the West, umami is still a rather exotic concept. It is actually a comparatively recent term even in Japan, though the taste has been known for centuries. It comes from a popular fish stock called dashi, which is made from seaweed and dried fish scales, and when added to other foods makes them even more delicious and imparts an ineffable but distinctive flavor. In the early twentieth century, a Tokyo chemist named Kikunae Ikeda determined to identify the source of the flavor and to try to synthesize it. In 1909, he published a brief paper in a Tokyo journal, identifying the source of the flavor as the chemical glutamate, an amino acid. He dubbed the flavor umami, meaning “essence of deliciousness.”
Ikeda’s discovery attracted virtually no attention outside Japan. The word “umami” isn’t recorded anywhere in English until 1963, when it appeared in an academic paper. Its first appearance in a more mainstream publication was in 1979 in New Scientist. Ikeda’s article wasn’t translated into English until 2002, after umami taste receptors had been confirmed by Western researchers. But in Japan, Ikeda became celebrated, not as a scientist so much, but rather as a co-founder of a great company, Ajinomoto, created to exploit his patent for making synthetic umami, in the form universally known today as monosodium glutamate, or MSG. Today Ajinomoto is a behemoth, making about one-third of all the world’s MSG.
MSG has had a hard time of it in the West since 1968 when The New England Journal of Medicine published a letter—not an article or a study, but simply a letter—from a doctor noting that he sometimes felt vaguely unwell after eating in Chinese restaurants and wondered if it was the MSG added to the food that was responsible. The headline on the letter was “Chinese-Restaurant Syndrome,” and from this small beginning it became fixed in many people’s minds that MSG was a kind of toxin. In fact, it isn’t. It appears naturally in lots of foods, like tomatoes, and has never been found to have deleterious effects on anybody when eaten in normal quantities. According to Ole G. Mouritsen and Klavs Styrbaek in their fascinating study, Umami: Unlocking the Secrets of the Fifth Taste, “MSG is the food additive that has been subjected to the most thorough scrutiny of all time,” and no scientist has ever found any reason to condemn it, yet its reputation in the West as a source of headaches and low-grade malaise now appears to be undimmed and permanent.
The tongue and its taste buds give us just the basic textures and attributes of food—whether they are soft or smooth, sweet or bitter, and so on—but the full sensuousness of it all is dependent on our other senses. It is nearly always wrong to talk about how food tastes, though of course we all do. What we appreciate when we eat is flavor, which is taste plus smell.*3
Smell is said to account for at least 70 percent of flavor, and maybe even as much as 90 percent. We appreciate this intuitively without often thinking about it. If someone hands you a pot of yogurt and says, “Is this strawberry?” your response will normally be to sniff it, not taste it. That is because strawberry is actually a smell, perceived nasally, not a taste in the mouth.
When you eat, most of the aroma reaches you not through your nostrils but by the back staircase of your nasal passage, what is known as the retronasal route, as opposed to the orthonasal route up your nose. An easy way to experience the limitations of your taste buds is to close your eyes, pinch shut your nostrils, and eat a flavored jelly bean collected blindly from a bowl. You will instantly apprehend its sweetness, but you almost certainly won’t be able to identify its flavor. But open your eyes and nostrils and its fruity specificity becomes immediately and redolently apparent. Even sound materially influences how delicious we find food. People who are played a range of crunching sounds through headphones while sampling potato chips from various bowls will always rate the crunchier, noisier chips as fresher and tastier, even though all the chips are the same.
Many tests have been done to demonstrate how easily we are fooled with respect to flavor. In a blind taste test at the University of Bordeaux, students in the faculty of enology were given two glasses of wine, one red and one white. The wines were actually identical except that one had been made a rich red with an odorless and flavorless additive. The students without exception listed entirely different qualities for the two wines. That wasn’t because they were inexperienced or naive. It was because their sight led them to have entirely different expectations, and this powerfully influenced what they sensed when they took a sip from either glass. In exactly the same way, if an orange-flavored drink is colored red, you cannot help but taste it as cherry.
The fact is that odors and flavors are created entirely inside our heads. Think of something delicious—a moist, gooey, warm chocolate brownie fresh from the oven, say. Take a bite and savor the velvety smoothness, the rich heady waft of chocolate that fills your head. Now consider the fact that none of those flavors or aromas actually exist. All that is really going in your mouth is texture and chemicals. It is your brain that reads these scentless, flavorless molecules and vivifies them for your pleasure. Your brownie is sheet music. It is your brain that makes it a symphony.
As with so much else, you experience the world that your brain allows you to experience.
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There is of course one other remarkable thing we do with our mouths and throats, and that is make meaningful noises. The ability to create and share complex sounds is one of the great wonders of human existence and the characteristic more than any other that sets us apart from all other creatures that have ever lived.
Speech and its evolution “are perhaps more extensively debated than any other topic in human evolution,” in the words of Daniel Lieberman. No one knows even approximately when speech began on Earth and whether it is an accomplishment confined to Homo sapiens or whether it was a skill mastered by archaic humans like Neanderthals and Homo erectus. Lieberman thinks it likely that Neanderthals commanded complex speech based on their large brains and array of tools, but it isn’t a provable hypothesis.
What is certain is that the capacity for speech requires a delicate and coordinated balance of tiny muscles, ligaments, bones, and cartilage of exactly the right length, tautness, and positioning in order to expel microbursts of modulated air in just the right measures. The tongue, teeth, and lips must also be nimble enough to take these throaty breezes and turn them into nuanced phonemes. And all of this must be achieved without compromising our ability to swallow or breathe. That’s quite a tall order, to put it mildly. It isn’t just a big brain that allows us to speak but an exquisite arrangement of anatomy. One reason chimps can’t talk is that they appear to lack the ability to make subtle shapes with tongue and lips to form complex sounds.
It may be that all this happened fortuitously in the course of an evolutionary redesign of our upper bodies to accommodate our new posture when we became bipedal, or it may be that some of these features were selected for through the slow, incremental wisdom of evolution, but the bottom line is that we ended up with brains big enough to handle complex thoughts and vocal tracts uniquely able to articulate them.
The larynx is essentially a box about an inch on each side. Within or around it are nine cartilages, six muscles, and a suite of ligaments, including two commonly known as the vocal cords but more properly known as the vocal folds. When air is forced through them, the vocal folds snap and flutter (like flags in a stiff breeze, it has been said), producing a variety of sounds, which are refined by tongue, teeth, and lips working together into the wondrous, resonant, informative exhalations known as speech. The three phases of the process are respiration, phonation, and articulation. Respiration is simply the pushing of air past the vocal ligaments; phonation is the process of turning that air into sound; and articulation is the refinement of sound into speech. If you wish to appreciate what a marvel speech is, try singing a song—“Frère Jacques” serves very well—and notice how effortlessly melodic the human voice is. The fact is, your throat is a musical instrument as well as a sluice and wind tunnel.*4
When you consider the complexity, it is hardly surprising that some people struggle to put it all together. Stuttering is one of the cruelest and least understood of everyday maladies. It affects 1 percent of adults and 4 percent of children. For reasons unknown, 80 percent of sufferers are male. The victims have included a great many distinguished figures—Aristotle, Virgil, Charles Darwin, Lewis Carroll, Winston Churchill (when young), Henry James, John Updike, Marilyn Monroe, and King George VI of Great Britain, who was sympathetically portrayed by Colin Firth in the 2010 movie The King’s Speech.
No one knows what provokes it or why different sufferers stumble over different letters or words in different positions in a sentence. It is more common among left-handers than right-handers, especially those who have been made to write right-handed. For many, the stammering miraculously ceases when they sing the words or speak another language or talk to themselves. The majority of speakers recover from the condition by their teenage years (which is why the proportion of child sufferers is so much higher than adult ones). Females seem to recover more easily than males.
