What Can Humans Know?

What are the perimeters of human knowledge? Perhaps not as broad and far-ranging as we like to think. Henry David Thoreau once famously wrote, “Who placed us with eyes between a microscopic and a telescopic world?” More recently, Jennifer Ackerman, author of Birds by the Shore, has offered an elegant paraphrase: “Humans, it is said, lie midway between the sun and the atom.”

When we look at the sky on a clear night, we can only see the 5,000 closest stars, and only one of the billions of galaxies that populate the rest of the universe. Our eyes are also unable to see what is smallest, not even what can be found on a grain of sand. Jennifer Ackerman writes, “A single grain of sand can support hundreds of colonies of bacteria, each composed of hundreds of individuals . . . all residing in the craters, scarps and troughs of the grain.”

Here I hold a small handful of sand from a beach around the corner of my home in Rhode Island. There must be tens of thousands of sand grains in my palm, and perhaps four hundred million or more bacteria living on them, none of which I can see.

Humbling, to imagine one’s biologically induced limitations, especially since we humans often unconsciously consider ourselves to be masters of the (or at least our) universe.

But our limitations are not only a matter of scale. Whales, for instance, can see us far more intricately than we can see them.

As Philip Hoare writes in The Sea Inside, whales “live in an element in which noise travels five times faster than in air. Their brains are wired for sound; their auditory cortex is larger than our visual cortex. Such a capacity is essential for animals that hunt in lightless depths. Theirs is a very different experience of the world from ours, because their world is so different. For toothed whales blessed with pin-sharp sonar accuracy, everything is transparent; nothing is concealed. They live in another dimension, able to see into and through the solid, to discern structures inside. A whale or dolphin can see the interior of my body as accurately as I can see the exterior of hers; I must resemble one of the educational models we had in school, clear plastic figurines of a man and a woman with their organs indecently displayed. The world is naked to a cetacean.”

Unlike us, whales (and dolphins too) can see through irrelevant clothes and the thin membrane of our skin. What is ordinary daily experience for them would be a superpower for us. Speaking of dolphins, they can send out two thousand clicks of sonar in a single second, enabling them to, as Philip Hoare reports, “discern something the thickness of a fingernail from thirty feet away.” Yet dolphins are capable of far more than such a comprehensive look-see. Hoare elaborates: dolphins “are able to use their sonar to detect one another’s emotional states by the way their temperature falls or rises, like a human lie-detector test. As a result they cannot dissemble about the way they feel, as we do. They know if another dolphin is angry or excited.”

This last startling tidbit I find especially humbling.

Throughout my teaching career, I pointed out to aspiring fiction writers that humans are biologically wired for isolation, because we cannot know what even our most intimate companion is thinking. Because of this, the “facts” of someone else’s inner life–all the years of that person’s memories and secret thoughts and desires–are great guesses on our part, hunches that the little we are able to see reflects the much more that we can’t. What passes for understanding of another is closer to the invention of a fictional character than we’d like to admit. That profound isolation from others’ thoughts is why art in all its forms was invented—particularly fiction, where a writer takes on the task of imagining others. I have to admit, I always assumed that any human’s exile from others’ thoughts applied to all living creatures. And yet, I learn—so late in life—that dolphins (and, I imagine, whales too) can “see” others’ emotions and cannot hide their own.

Our awareness of the world’s mysterious life in all its facets is a narrow path. Of all our five senses, sight is supposed to be our strongest suit, and yet we are no match for birds, who, Philip Hoare writes, “are thought to possess photopigments in their eyes known as cryptochromes that detect the magnetic field chemically, seeing it as a pattern of colors or lights which enables them to navigate.”

So much for our vaunted powers of sight! As for other senses, such as taste, touch and smell, the (not so) lowly lobster puts us to shame. The bodies of lobsters, Jennifer Ackerman tells us, “are covered with odor-sensitive receptors that detect minute concentrations of pheromones, chemicals they use for nearly every activity from tracking prey to announcing sexual prowess. Thin hairs on the antennules have more than four hundred different kinds of receptor cell, each tuned to a specific chemical compound. Just as birds can distinguish myriad notes packed into a brief musical interval, lobsters can read a spectrum of chemicals in a teaspoon of seawater.”

A spectrum of chemicals we remain unaware of, however often we splash about in a pond, a lake, a bay. Wet, to us, is wet. How limited we are, what ordinary creatures with only modest physical talents. And yet, we possess imaginations that lift us above our limitations. We live in a world of books, music, art, dance, sculpture and architecture; what we create in myriad forms, the world we live in, is an elaborate carapace of inventiveness that we exude in much the same way a snail exudes its elaborate spiraled shell—as something we must do, an essential urge that is simply and always will be a part of us. And yet, how important it is to remember, in comparison with our fellow creatures in the world, how little we truly see, how little we ultimately know.


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