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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.)