The Beholder's Eye

From a book about perception called "A Natural History of the Senses":

"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 thier heads, so they can use binocular vision to sight and track their prey. Our eyes have separate mechanisms that agther light, pick out an important or novel image, focus on it precisely, pinpoint it in space, and follow it... 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....

Though most of us don't hunt, our eyes are still the monopoly 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 feilds and up the mountains, travel across time, country, and parsecs of outer space, and collect bushel baskets of information as it goes...

The process of seeing began very simply. In 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 constantly be bathed in salt water...

We think of our eyes as wise seers, but all the eye does is gather light.... The iris of the eye, which is really a muscle, changes the size of a small hole, the pupil, through which light enters the eyeball... In addition to its gate-keeping function, the iris 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 refelcting other colors whose rays are longer. They therfore 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...."