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  No other part of the body has received more misguided attention, or proved more resistant to scientific understanding, than the head. The nineteenth century in particular was something of a golden age in this respect. The period saw the rise of two distinct but often confused disciplines, phrenology and craniometry. Phrenology was the practice of correlating bumps on a skull with mental powers and attributes of character, and it was always a marginal pursuit. Craniometrists virtually without exception dismissed phrenology as crackpot science while promulgating an alternative nonsense of their own. Craniometry focused on more precise and comprehensive measurements of volume, shape, and structure of the head and brain but in pursuit, it must be said, of equally preposterous conclusions.*1

  The greatest cranial enthusiast of all, now forgotten but once very famous indeed, was Barnard Davis (1801–81), a doctor in the English Midlands. Davis became gripped by craniometry in the 1840s and rapidly made himself into the world’s supreme authority. He produced a stream of books with weighty titles like On the Peculiar Crania of the Inhabitants of Certain Groups of Islands in the Western Pacific and Contributions Towards Determining the Weight of the Brain in Different Races of Man. These were surprisingly popular. On Synostotic Crania Among Aboriginal Races of Man went through fifteen editions. The epic Crania Britannica, published in two volumes, had thirty-one editions. Davis became so celebrated that people from all over the world, among them the president of Venezuela, left their skulls for him to study. Gradually, he built up the world’s largest collection of skulls—1,540 in all, or more than all the skulls in all the world’s other institutions combined.

  Davis would stop at almost nothing to enlarge his collection. When he wished for skulls from the indigenous people of Tasmania, he wrote to George Robinson, official protector of aborigines, for a selection. Because the plundering of aboriginal graves had by this time become a criminal act, Davis supplied Robinson with detailed instructions on how to remove a skull from an indigenous Tasmanian and replace it with the skull of any convenient surrogate in a way that would avoid arousing suspicions. He was evidently successful in his endeavors, for his collection soon included sixteen Tasmanian skulls and one whole skeleton.

  Davis’s fundamental ambition was to prove that dark-skinned people were created separately from light-skinned people. He was convinced that a person’s intellect and moral compass were indelibly written in the curves and apertures of the skull and that these were exclusively products of race and class. People with “cephalic peculiarities” should be treated “not as criminals but as dangerous idiots,” he suggested. In 1878, at the age of seventy-seven, he married a woman fifty years his junior. What her cranium was like is unknown.

  This instinct on the part of European authorities to prove all other races inferior was widespread, if not universal. In England, in 1866 the eminent physician John Langdon Haydon Down (1828–96) first described the condition that we now know as Down’s syndrome in a paper called “Observations on an Ethnic Classification of Idiots,” but he referred to it as “Mongolism” and its victims as “Mongoloid idiots” in the belief that they were suffering an innate regression to an inferior, Asiatic type. Down believed, and no one seems to have doubted him, that idiocy and ethnicity were conjoined qualities. He also listed “Malay” and “Negroid” as regressive types.

  In Italy, meanwhile, Cesare Lombroso (1835–1909), the country’s most eminent physiologist, developed a parallel theory called criminal anthropology. Lombroso believed that criminals were evolutionary throwbacks who betrayed their criminal instincts through a range of anatomical features—slope of the forehead, whether their earlobes were rounded or spade shaped, even the amount of spacing between their toes. (People with a lot of toe space were closer to apes, he explained.) Though his assertions were without the faintest scientific validity, Lombroso was widely esteemed and is even now sometimes referred to as the father of modern criminology. Lombroso was frequently called as an expert witness. In one case, cited by Stephen Jay Gould in The Mismeasure of Man, he was asked to determine which of two men had killed a woman. Lombroso declared one man self-evidently guilty because he had “enormous jaws, frontal sinuses and zygomata, thin upper lip, huge incisors, unusually large head [and] tactile obtuseness with sensorial manicinism.” Never mind that no one knew what much of that meant and that there was no actual evidence against the poor fellow. He was found guilty.

  But the most influential, and unexpected, practitioner of craniometry was the great French anatomist Pierre Paul Broca (1824–80). Broca was without question a brilliant scientist. In 1861, during an autopsy on a stroke victim who hadn’t spoken for years except to repeat endlessly the syllable “tan,” Broca discovered the brain’s speech center in the frontal lobe—the first time that anyone had connected an area of the brain to a specific action. The speech center is still called Broca’s area, and the impediment Broca discovered is Broca’s aphasia. (Under it, a person can understand speech but can’t reply except to utter meaningless noises or sometimes stock phrases like “I’ll say” or “Oh, boy.”)

  Broca was less astute, however, with respect to character traits. He was convinced, even when all the evidence was against him, that females, criminals, and dark-skinned foreigners had smaller, less agile brains than their white male counterparts. Whenever Broca was presented with evidence that contradicted this, he disregarded it on the grounds that it must be flawed. He was similarly disinclined to believe a study from Germany showing that German brains were on average a hundred grams weightier than French ones. He explained this awkward discrepancy by suggesting that the French subjects were very old when tested and that their brains had shrunk. “The degree of decadence that old age can impose upon a brain is very variable,” he observed. He also had problems accounting for why executed criminals sometimes had big brains, and decided that their brains had become artificially engorged by the stress of hanging. The greatest indignity of all came when Broca’s own brain was measured upon his death and was found to be smaller than average.

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  The person who finally put the study of the human head on something like a sound scientific foundation was none other than the great Charles Darwin. In 1872, thirteen years after he published On the Origin of Species, Darwin produced another landmark work, The Expression of the Emotions in Man and Animals, which looked at expressions reasonably and without prejudice. The book was revolutionary not just for being sensible but for observing that certain expressions appear to be common to all peoples. This was a much bolder utterance than we may realize today because it underlined Darwin’s conviction that all people, whatever their race, have a common heritage, and that was a very revolutionary thought in 1872.

  What Darwin realized was something that all babies know instinctively—that the human face is highly expressive and instantly captivating. No two authorities seem to agree on quite how many expressions we can make—estimates range from forty-one hundred to ten thousand—but it is clearly a large number. More than forty muscles, a significant portion of the body’s total, are involved in facial expression. Babies fresh from the womb are said to prefer a face, or even the general pattern of a face, to any other shape. Whole regions of the brain are devoted solely to recognizing faces. We are exquisitely sensitive to the subtlest alterations of mood or expression, even if we are not always conscious of them. In an experiment related by Daniel McNeill in his book The Face, men were shown two photos of women that were identical in every respect except that the pupils had been subtly enlarged in one. Although the change was too slight to be consciously perceived, the test subjects invariably found the women with larger pupils more attractive, though they were at a loss to explain why.

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  In the 1960s, nearly a century after Darwin wrote The Expression of the Emotions, Paul Ekman, a professor of psychology at the University of California at San Francisco, decided to test the universality, or not, of facial expressions by studying remote tribal people in New Guinea who had no acquaintance with Western habits. Ekman concluded that six expressions are universal: fear, anger, surprise, pleasure, disgust, and sorrow. The most universal expression of all is a smile, which is rather a nice thought. No society has ever been found that doesn’t respond to smiles in the same way. True smiles are brief—between two-thirds of a second and four seconds. That’s why a held smile begins to look menacing. A true smile is the one expression that we cannot fake. As the French anatomist G.-B. Duchenne de Boulogne noticed as long ago as 1862, a genuine, spontaneous smile involves the contraction of the orbicularis oculi muscle in each eye, and we have no independent control over those muscles. You can make your mouth smile, but you can’t make your eyes sparkle with feigned joy.

  According to Paul Ekman, we all indulge in “microexpressions”—flashes of emotion, no more than a quarter of a second in duration, that betray our true inner feelings regardless of what our more general, controlled expression is conveying. Nearly all of us miss these telltale expressions, according to Ekman, but we can be taught to spot them, assuming we want to know what workmates and loved ones really think of us.*2

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  By primate standards, we have a very odd head. Our faces are flat, our foreheads high, and our noses protuberant. Almost certainly a number of factors are responsible for our distinctive facial arrangements—our upright posture, our biggish brain, our diet and lifestyle, the fact that we are built for sustained running (which affects how we breathe), and the things that we find adorable in a mate. (Dimples, for instance—not something that gorillas look for when feeling frisky.)

  Surprisingly, given how central faces are to our existence, quite a lot about them is still a mystery to us. Take eyebrows. All the many species of hominids that preceded us had prominent browridges, but we Homo sapiens gave them up in favor of our small, active eyebrows. It’s not easy to say why. One theory is that eyebrows are there to keep sweat out of the eyes, but what the eyebrows do really well is convey feelings. Think how many messages you can send with a single arched eyebrow, from “I find that hard to believe” to “Watch your step” to “Care to have sex?” One of the reasons the Mona Lisa looks enigmatic is that she has no eyebrows. In one interesting experiment, subjects were shown two sets of digitally doctored photographs of well-known people: one with the eyebrows eliminated and the other with the eyes themselves taken away. Surprisingly, but overwhelmingly, volunteers found it harder to identify the celebrities without eyebrows than without eyes.

  Eyelashes are similarly uncertain. There is some evidence to suggest that eyelashes subtly change airflow around the eye, helping to waft away motes of dust and other tiny particulates from landing there, but the main benefit is probably that they add interest and allure to faces. People with long eyelashes are generally rated more attractive than those without.

  Even more anomalous is the nose. It is the convention among mammals to have snouts, not round, projecting noses. According to Daniel Lieberman, professor of human evolutionary biology at Harvard, our external nose and intricate sinuses evolved to help with breathing efficiency and with keeping us from becoming overheated on long runs. It is an arrangement that has clearly suited us, for humans and their ancestors have had projecting noses for some two million years.

  Most mysterious of all is the chin. The chin is unique to humans, and no one knows why we have one. It doesn’t seem to confer any structural benefit to the head, so it may be simply that we find a good chin dashing. Lieberman, in a rare moment of lightness, observed, “Testing this last hypothesis is especially difficult, but the reader is encouraged to think of appropriate experiments.” It is certainly the case that we talk about “chinless wonders” and otherwise equate modest chins with deficiencies of character and intellect.

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  Much as we all appreciate a pert nose or gorgeous eyes, the real purpose of most of our facial features is to help us interpret the world through our senses. It’s curious that we always speak of our five senses because we have way more than that. We have a sense of balance, of acceleration and deceleration, of where we are in space (what is known as proprioception), of time passing, of appetite. Altogether (and depending on how you count them) we have as many as thirty-three systems within us that let us know where we are and how we are doing.

  We’ll explore the sense of taste in the next chapter when we venture into the mouth, but let’s look now at the three other most familiar senses of the head: sight, hearing, and smell.

  SIGHT

  THE EYE IS a thing of wonder, needless to say. About a third of your entire cerebral cortex is engaged with vision. Victorians so marveled at the intricacy of the eye that they often cited it as proof of intelligent design. It was an odd choice because the eye is really rather the reverse—literally so, for it is built back to front. The rods and cones that detect light are at the rear, but the blood vessels that keep it oxygenated are in front of them. There are vessels and nerve fibers and other incidental detritus all over, and your eye has to see through all this. Normally, your brain edits out any interference, but it doesn’t always succeed. You might have had the experience of looking at a clear blue sky on a sunny day and seeing little white sparks popping in and out of existence, like the briefest of shooting stars. What you are seeing, amazingly enough, is your own white blood cells, moving through a capillary in front of the retina. Because white blood cells are big (compared with red blood cells), they sometimes get stuck briefly in the narrow capillaries, and that is what you are seeing. The technical name for these disturbances is Scheerer’s blue field entoptic phenomena (named for a German ophthalmologist of the early twentieth century, Richard Scheerer), though they are more commonly and poetically known as blue sky sprites. They are especially visible against a bright blue sky simply because of the way the eye absorbs different wavelengths of light.

  Floaters are a similar phenomenon. They are clumps of microscopic fibers in the jellylike vitreous humor of your eye, which cast a shadow on the retina. Floaters are a common occurrence as you get older, and are generally harmless, though they can indicate a retinal tear. The technical name for them, if you wish to impress someone, is muscae volitantes, or “hovering flies.”

  If you held a human eyeball in your hand, you might be surprised by its size because we only see about one-sixth of it when it is embedded in the eye socket. The eye feels like a gel-filled bag, which is not surprising, because it is filled with a gel-like material, the aforementioned vitreous humor. (Humor in its anatomical sense signifies any fluid or semifluid in the body and not, obviously, its ability to generate laughs.)

  As you would expect of a complex instrument, the eye has many parts, some of which are well known to us by name (iris, cornea, retina) and others of which are more obscure (fovea, choroid, sclera), but essentially it is a camera. The front part—the lens and cornea—captures passing images and projects them onto the back wall of the eye—the retina—where photoreceptors convert them into electrical signals that are passed on to the brain via the optic nerve.

  If there is one part of your visual anatomy that deserves a moment’s thanks, it is the cornea. This modest, dome-shaped goggle not only protects the eye from worldly assaults but actually does two-thirds of the eyeball’s focusing. The lens, which gets all the credit in the popular mind, does only about a third of the focusing. The cornea could hardly be less imposing. If you were to pop it out and lay it on the tip of your finger (where it would fit very comfortably), it wouldn’t seem much at all. But on closer examination, as with almost every part of the body, it is a wonder of complexity. It has five layers—epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium—laminated into a space just slightly over half a millimeter thick. In order to be transparent, it has a very modest blood supply—indeed, practically none. The part of the eye that has the most photoreceptors—that really does the seeing—is called the fovea (from a Latin word for “shallow pit”; the fovea inhabits a slight depression). It is interesting that such a crucial part is one that most of us have never heard of.

  To keep all this working smoothly (in the most literal sense), we produce tears constantly. Tears not only keep our eyelids gliding smoothly but also even out tiny imperfections on the eyeball surface, making focused vision possible. They also contain antimicrobial chemicals, which successfully keep most pathogens at bay. Tears come in three varieties: basal, reflex, and emotional. Basal are the functional ones that provide lubrication. Reflex tears are those that emerge when the eye is irritated by smoke or sliced onions or similar. And emotional tears are of course self-evident, but they are also unique. We are the only creatures that cry from feeling, as far as we can tell. Why we do so is another of life’s many mysteries. We get no physiological benefit from erupting in tears. It is also a little odd surely that this act signifying powerful sadness is also triggered by extreme joy or quiet rapture or intense pride or almost any other potent emotional state.*3

  Producing tears involves an extraordinary number of tiny glands around the eyes—namely, the Glands of Krause, Wolfring, Moll, and Zeis, as well as nearly four dozen Meibomian glands in the eyelids. Altogether you produce about five to ten ounces of tears a day. The tears drain away through holes known as puncta on the little fleshy knob (known as the papilla lacrimalis) in the corner of each eye beside the nose. When you cry emotionally, the puncta cannot drain the fluid fast enough, so it overflows your eyes and runs down your cheeks.

  The iris is what gives the eye its color. It is composed of a pair of muscles that adjust the opening of the pupil, rather like the aperture on a camera, to let in or keep out light as needed. Superficially, the iris looks like a neat ring, encircling the pupil, but closer inspection shows that it is in fact “a riot of spots, wedges, and spokes,” in the words of Daniel McNeill, and these patterns are unique to each of us, which is why iris recognition devices are now increasingly used to identify us at security checkpoints.