Explore the Hidden Wonders Around Us

It is an immense world, and we only see bits of it, but our sensory pollutions have left few refuges.”

Dusk, late summer. A deer works the edge of the pasture. A lonely frog, peeping, is answered by a cricket. As the light slips, a bat skitters in and out of the shrinking circle I can see.

Why do I not do this more often, let the night steal my usual senses away, leave me exposed?

It grows dark. The deer fades like a ghost. I am reborn through other senses, alive to the slightest brush of air. I cannot quite see the deer anymore but I can sense its movement. The muffled hoots of a great horned owl roll through the air. A melodic note — what is it? — sounds from the edge of the — there. A robin. It cuts its evening song short with a restless upswing. Night. Almost fall. Full of creatures great and small.

The edges of perception: this is the terrain of science writer Ed Yong’s latest journey, a book called “An Immense World: How Animal Senses Reveal the Hidden Realms Around Us.”

Reading it is like running your fingers through a treasure chest of jewels — not that I’ve had that experience, but it’s something I can imagine, just as I can imagine, with Yong’s deft help, what it might be like to be a wild animal with its own way of perceiving the world. The book teems. Why does it feel like a rare and precious experience these days to be wowed by Earth’s biodiversity, left with a sense of incredible magic?

The backbone of “An Immense World” is the concept of Umwelt, a term coined by Baltic-German zoologist Jakob von Uexküll in 1909. An animal’s Umwelt is its perceptual world, or self-world: all the things it can hear, see, taste, feel, smell, or detect thermally or electrically or magnetically (I wrote about this in my first piece for KP News, “A Newt’s World” November 2019).

That deer on the edge of the pasture. As my vision faded, its vision came into its own. Though its eyes have fewer cone photoreceptors than mine, giving it poorer daytime color vision, its highly concentrated rods give it excellent low-light vision, and a reflective surface at the back of its eye sends light back across its photoreceptors for double absorption. Thanks to the deer’s horizontal pupils, packed with rods, the area of sharpest focus in its field of vision is not a small central circle like ours but a horizontal band. And because of its bulging eyes, this band extends in a 300-degree arc around its head.

Layer upon layer, the book builds an immense world of overlapping Umwelten. An animal’s Umwelt is defined as much by what it lacks as what it includes. “Nothing can sense everything, and nothing needs to,” writes Yong. Trichromatic color vision with high resolution — humankind’s most notable sense — places massive energy demands on our brains. Most animals have no need to expend that kind of energy. Other perceptions are more important for survival. An animal’s Umwelt reveals much about its evolved relationship with life.

A great horned owl’s ears are buried in its facial feathers, which, disc-shaped, can be molded to catch sound like a satellite dish. One ear is higher in the skull than the other. While I can pinpoint a sound’s source fairly well in the horizontal plane — it arrives in one ear fractionally earlier than the other — I struggle in the vertical plane. A sound above me hits both ears at the same time. The owl’s offset ears give it the ability to pinpoint scurrying small mammals in both the horizontal and the vertical planes, important for an animal that hunts from on high.

Crickets have ears on their knees. Insects have evolved ears at least 19 times on mouths, chests, abdomens, antennae. And yet most insects are deaf, perfectly fine without any ears at all. Frogs tune their calls to catch the frequencies best heard by potential mates, which drives the evolution of both frogs and the ears of their predators. Spiders live in a world of vibrations; treehoppers in rumbling music they send and sense as tremors in the plants on which they live. Songbirds experience their songs in a far more nuanced way than we hear them. The tiny hairs in songbird ears change when the season changes, optimizing themselves to hear fast in fall, when urgent messages keep flocks tight and safe, and to hear pitch with precision in spring when song determines who mates.

“An Immense World” makes one continually ask, Why do we have our senses tuned the way we do? What are we missing? Why? As Yong writes, “The boundaries of the human Umwelt often make the Umwelten of others opaque to us.”

At the same time, Umwelten level the playing field of life. Humankind has a long history of putting technologies, such as senses, in a hierarchy, ranking them as inferior or superior. Thinking in terms of Umwelten allows us to see that even the simplest of eyes, such as those on the lips of scallops, are perfectly adapted to the scallop’s needs. Instead of hierarchies, Umwelten give us radiant diversity.

“Our intuitions will be our biggest liabilities,” Yong suggests, “and our imaginations will be our greatest assets.”

“An Immense World” ends with a brief but explosive chapter on the pollution of sensescapes. A corollary to the idea that our sensory bias makes it difficult for us to enter other Umwelten is the fact that sensory pollution does not appear as such to us. Noises, lights, chemical signals, winds, odors, and electrical fields that to us are nuisances may be world-shattering to other creatures, seriously jeopardizing their ability to survive in this world.

It is an immense world, and we only see bits of it, but our sensory pollutions have left few refuges. Yong takes a hopeful stance here. Sources of sensory pollution, he suggests, unlike long-lasting chemicals or atmospheric carbon, can be switched off as soon as we choose.