A Natural History of the Senses (34 page)

Look in the mirror. The face that pins you with its double gaze reveals a chastening secret: You are looking into a predator’s eyes. Most predators have eyes set right on the front of their heads, so they can use binocular vision to sight and track their prey. Our eyes have separate mechanisms that gather the light, pick out an important or novel image, focus it precisely, pinpoint it in space, and follow it; they work like top-flight stereoscopic binoculars. Prey, on the other hand, have eyes at the sides of their heads, because what they really need is peripheral vision, so they can tell when something is sneaking up behind them. Something like us. If it’s “a jungle out there” in the wilds of the city, it may be partly because the streets are jammed with devout predators. Our instincts stay sharp, and, when necessary, we just decree one another prey and have done with it. Whole countries sometimes. Once we domesticated fire as if it were some beautiful temperamental animal; harnessing both its energy and its light, it became possible for us to cook food to make it easier to chew and digest, and, as we found out eventually, to kill germs. But we can eat cold food perfectly well, too, and did for thousands of years. What does it say about us that, even in refined dining rooms, our taste is for meat served at the temperature of a freshly killed antelope or warthog?

Though most of us don’t hunt, our eyes are still the great monopolists of our senses. To taste or touch your enemy or your food, you have to be unnervingly close to it. To smell or hear it, you can risk being farther off. But vision can rush through the fields and up the mountains, travel across time, country, and parsecs of outer space,
and collect bushel baskets of information as it goes. Animals that hear high frequencies better than we do—bats and dolphins, for instance—seem to see richly with their ears, hearing geographically, but for us the world becomes most densely informative, most luscious, when we take it in through our eyes. It may even be that abstract thinking evolved from our eyes’ elaborate struggle to make sense of what they saw. Seventy percent of the body’s sense receptors cluster in the eyes, and it is mainly through seeing the world that we appraise and understand it. Lovers close their eyes when they kiss because, if they didn’t, there would be too many visual distractions to notice and analyze—the sudden close-up of the loved one’s eyelashes and hair, the wallpaper, the clock face, the dust motes suspended in a shaft of sunlight. Lovers want to do serious touching, and not be disturbed. So they close their eyes as if asking two cherished relatives to leave the room.

Our language is steeped in visual imagery. In fact, whenever we compare one thing to another, as we constantly do (consider the country expression: “It was raining harder than a cow pissing sideways on a rock”), we are relying on our sense of vision to capture the action or the mood. Seeing is proof positive, we stubbornly insist (“I saw it with my own eyes …”). Of course, in these days of relativity, feats of magic, and tricks of perception, we know better than to trust everything we see (“… a flying saucer landed on the freeway …”). See with our naked eyes, that is. As Dylan Thomas reminds us, there are many “fibs of vision.”
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If we extend our eyes by attaching artificial lenses and other accessories to our real ones
(glasses, telescopes, cameras, binoculars, scanning electron microscopes, CAT scans, X-rays, magnetic resonance imaging, ultrasound, radioisotope tracers, lasers, DNA sequencers, and so on), we trust the result a little more. But Missouri is still called the
Show Me!
state, which, as a kind of visual pun, I guess, it displays on its license plates for motorists to see. “The writing is on the wall,” a politician says sagely, forgetting temporarily that it could be a forgery nonetheless. We quickly see through people whose characters are transparent. And, heaven knows, we yearn for enlightenment. “I see where you’re coming from,” one woman says to another in a café, “but you’d better watch out, he’s bound to see what you’re up to.”
See for yourself!
the impatient exclaim to disbelievers. After the Bible’s first imperative—“Let there be light”—God viewed each day’s toil and “saw that it was good.” Presumably, He, too, had to see it to believe it. Ideas dawn on us, if we’re bright enough, not dim-witted, especially if we’re visionary. And, when we flirt, though the common phrase sounds quite ghoulish and extreme, we give someone the eye.

The process of seeing began very simply. In the ancient seas, life-forms developed faint patches of skin that were sensitive to light. They could then tell light from dark, and also the direction of the light source, but that was all. These skills turned out to be so useful that eyes evolved that could judge motion, then form, and finally a dazzling array of details and colors. One reminder of our oceanic origins is that our eyes must be constantly bathed in salt water. Some of the oldest eyes on record are those of the trilobite, one of the great success stories of the Cambrian age, which we now know only through its plentiful fossil remains. As I type this, I am wearing on a chain around my neck a small trilobite fossil, set in a silver bezel. Five hundred million years ago, it thrived in the swamps, with compound faceted eyes that could see mainly sideways but, unfortunately, not up. On the other hand, the newest eyes are those we have invented, such as the electric eye (based on what we learned about the motion-detecting design of the frog’s eye), or the mirror telescope (based on the contrast-judging design of the horseshoe crab’s eye), or synchronous lenses for use in microsurgery, optical scanning, and severe vision problems (based on the double lens of copilia, a
myopic crustacean that lives deep in the Mediterranean). Although plants do not have eyes, Loren Eiseley argues eloquently for the eye of the fungus pilobolus, which has a light-sensitive area that controls the spore cannon it aims at the brightest spot it can find.

We think of our eyes as wise seers, but all the eye does is gather light. Let’s consider the light-harvesting. As we know, the eye works a lot like a camera; or rather, we invented cameras that work like our eyes. To focus a camera, you move the lens closer to or farther away from an object. The eye’s rubbery, bean-shaped crystalline lens achieves the same result by changing its shape—the lens thins to focus on a distant object, which looks small; thickens to focus on a near one, which looks large. A camera can control the amount of light it allows in. The iris of the eye, which is really a muscle, changes the size of a small hole, the pupil,
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through which the light enters the eyeball. Because fish don’t have this pupillary response, in which the iris protects against sudden surges of light, and most of them do not have eyelids (since their eyes are constantly bathed in water), they’re much more susceptible to dazzlement than we are. In addition to its gate-keeping function, the iris, named after the Greek word for rainbow, is what gives our eyes their color. Caucasian eyes appear blue at birth, Negro eyes brown. After death, Caucasian eyes appear greenish-brown. Blue eyes are not inherently blue, not
stained
blue like fabric: They appear blue because they have less pigment than brown eyes. When light enters “blue” eyes, the very short blue light rays scatter as they jump off tiny, nonpigmented particles; what we see are the scattered rays, and the eyes appear to be blue. Dark eyes have densely packed pigment molecules and absorb the blue wavelengths, at the same time reflecting other colors whose rays are longer. They therefore appear to be brown or hazel. Though on casual inspection irises may look pretty much the same, the pattern of color, starbursts, spots, and other features is so highly
individual that law-enforcement people have considered using iris patterns in addition to fingerprints.

At the back of a camera, film records the images. Lining the rear wall of the eyeball is a thin sheet, the retina, which includes two sorts of photosensitive cells, rods and cones. We need two because we live in the two worlds of darkness and light. A hundred and twenty-five million thin, straight rods construe the dimness, and report in black and white. Seven million plump cones examine the bright, color-packed day. There are three kinds of cones, specializing in blue, red, and green. Mixed together, the rods and cones allow the eye to respond quickly to a changing scene. One place on the retina, where the optic nerve enters the brain, has no rods or cones at all and, as a result, does not perceive light; we refer to it as our “blind spot.” But right in the middle of the retina lies a small crater, the fovea, filled with highly concentrated cones, which we use for precision focusing when we want to examine an object in bright light, to drag it into sharp view and grip it with our eyes. Because the fovea is so small, it can perform its magic only on a small area (a four-inch-square snapshot at eight feet, for example). Almost every cone in a fovea has its own direct line to higher centers in the brain; elsewhere on the retina, rods and cones may serve many cells, and vision is vaguer. The eyeball moves subtly, continuously, to keep an object in front of the fovea. In dim light, the fovea’s cones are almost useless; instead we must look just “off” of an object to see it clearly with the surrounding rods, not directly at it because the fovea would fail us and the object appear invisible. Because the rods see no color, we don’t perceive color at night. When the retina observes something, neurons pass the word along to the brain through a series of electrochemical handshakes. In about a tenth of a second, the message reaches the visual cortex, which begins to make sense of it.

However, seeing, as we think of it, doesn’t happen in the eyes but in the brain. In one way, to see flamboyantly, in detail, we don’t need the eyes at all. We often remember scenes from days or even years earlier, viewing them in our mind’s eye, and can even picture completely imaginary events, if we wish. We see in surprising detail
when we dream. Sometimes when I’m in a visually besotting landscape, somewhere out in nature and experiencing intense rapture, I lie down at night and close my eyes, and see the landscape parading across the inside of my closed lids. The first time this happened—on a 200,000-acre working cattle ranch, surrounded by pastel mesas, in the New Mexico desert—I was a little spooked. Wrung out from the rigors of the branding corral, I needed sleep, but all the day’s images, gestures, and motions still blazed in my visual memory. It was not like dreaming: it was like trying to sleep with your eyes wide open during a fiesta in full swing.

The same thing happened more recently, this time in Antarctica. One sunny day, we cruised through Gerlache Strait, which narrows to 1600 feet at its southern end; ice mountains towered on either side of the ship. Black jagged mountains, covered in cascading snow and ice, looked like penguins standing in familiar postures in a wash of brilliant light. While real penguins porpoised beside the boat, huge icebergs floated by, with bases of pale blue and sides of mint green. In the ship’s glassed-in observation deck, people sat in armchairs at the window, some dozing. One man held out his pinky and first finger as if giving someone the evil eye, but he was measuring an iceberg. Deception Island, though distant, looked close and clear in the sterile air. A crib of ice holding a soft blue wash in its palms drifted close to the ship. Across the strait, ice calved off a glacier with a loud explosive crumble. Pastel icebergs roamed around us, some tens of thousands of years old. Great pressure can push the air bubbles out of the ice and compact it. Free of air bubbles, it reflects light differently, as blue. The waters shivered with the gooseflesh of small ice shards. Some icebergs glowed like dull peppermint in the sun—impurities trapped in the ice (phytoplankton and algae) tinted them green. Ethereal snow petrels flew around the peaks of the icebergs, while the sun shone through their translucent wings. White, silent, the birds seemed to be pieces of ice flying with purpose and grace. As they passed in front of an ice floe, they became invisible. Glare transformed the landscape with such force that it seemed like a pure color. When we went out in the inflatable motorized rafts called Zodiacs to tour the iceberg orchards, I
grabbed a piece of glacial ice and held it to my ear, listening to the bubbles cracking and popping as the air trapped inside escaped. And that night, though exhausted from the day’s spectacles and doings, I lay in my narrow bunk, awake with my eyes closed, while sunstruck icebergs drifted across the insides of my lids, and the Antarctic peninsula revealed itself slowly, mile by mile, in the small theater of my closed eyes.

Because the eye loves novelty and can get used to almost any scene, even one of horror, much of life can drift into the vague background of our attention. How easy it is to overlook the furry yellow comb inside the throat of an iris, or the tiny fangs of a staple, or the red forked tongue of a garter snake, or the way intense sorrow makes people bend their bodies as if they were blowing in a high wind. Both science and art have a habit of waking us up, turning on all the lights, grabbing us by the collar and saying
Would you please pay attention!
You wouldn’t think something as complexly busy as life would be so easy to overlook. But, like supreme racehorses, full of vitality, determination, and heart, we tend to miss sights not directly in our path—the colorful crowds of people on either side, the shapes left in the thickly rutted track, and the permanent spectacle of the sky, that ever-present, ever-changing pageant overhead.