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Kindle Notes & Highlights
by
Ed Yong
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February 27 - March 31, 2025
Earth teems with sights and textures, sounds and vibrations, smells and tastes, electric and magnetic fields. But every animal can only tap into a small fraction of reality’s fullness. Each is enclosed within its own unique sensory bubble, perceiving but a tiny sliver of an immense world.
Umwelt comes from the German word for “environment,” but Uexküll didn’t use it simply to refer to an animal’s surroundings. Instead, an Umwelt is specifically the part of those surroundings that an animal can sense and experience—its perceptual world.
Our Umwelt is still limited; it just doesn’t feel that way. To us, it feels all-encompassing. It is all that we know, and so we easily mistake it for all there is to know. This is an illusion, and one that every animal shares.
Perhaps people who experience the world in ways that are considered atypical have an intuitive feeling for the limits of typicality.
The Umwelt concept can feel constrictive because it implies that every creature is trapped within the house of its senses. But to me, the idea is wonderfully expansive. It tells us that all is not as it seems and that everything we experience is but a filtered version of everything that we could experience.
As the writer Marcel Proust once said, “The only true voyage…would be not to visit strange lands but to possess other eyes…to see the hundred universes that each of them sees.” Let us begin.
The next time you look at a dog’s nose, notice that the front-facing holes taper off into side-facing slits. When the animal exhales while sniffing, air exits through those slits and creates rotating vortices that waft fresh odors into the nose. Even when breathing out, a dog is still sucking air in.
But after a summer of sniffing, those behavioral quirks diminished. The reticent dogs regained their volition. The reactive dogs became tolerant. All seemed more easygoing.
Horowitz found that dogs became more optimistic after just two weeks of nosework. As their sense of smell brightened, so did their outlook. (By contrast, dogs didn’t change after two weeks of heelwork—an owner-led obedience activity that involves neither olfaction nor autonomy.)
Let dogs be dogs. Appreciate that their Umwelt is different, and lean into that difference. She does this by taking Finn on dedicated smell walks, when he’s allowed to sniff to his olfactory bulb’s content. If he stops, she stops. His nose sets the pace. The walks are slower, but she has no destination in mind.
Odorant receptors can also vary from one individual to another in dramatic ways. For example, the OR7D4 gene creates a receptor that responds to androstenone, the chemical behind the stench of sweaty socks and body odor. To most people, it’s repulsive. But to a lucky few who inherit a slightly different version of OR7D4, androstenone smells like vanilla.
From a biological perspective, perhaps the most wondrous thing about light is that we can sense it at all.
The gradations Darwin imagined do indeed exist: Animals have every conceivable intermediate from simple photoreceptors to sharp eyes. And different animal groups have repeatedly and independently evolved diverse eyes using the same opsin building blocks. The jellyfish alone have evolved stage-two eyes at least nine times, and stage-three eyes at least twice. Eyes, far from being a blow to evolutionary theory, have proved to be one of its finest exemplars.[*8]
The first step to understanding another animal’s Umwelt is to understand what it uses its senses for.
An animal’s visual acuity is measured in cycles per degree—a concept that, by happy coincidence, you can think of in terms of zebra stripes. Stretch out your arm and give a thumbs-up. Your nail represents roughly 1 degree of visual space, out of the 360 degrees that surround you. You should be able to paint 60 to 70 pairs of thin black-and-white stripes on that nail and still be able to tell them apart. A human’s visual acuity, then, is somewhere between 60 and 70 cycles per degree, or cpd.
Aside from raptors, only other primates come close to our standards. Octopuses (46 cpd), giraffes (27 cpd), horses (25 cpd), and cheetahs (23 cpd) do reasonably well. A lion’s acuity is only 13 cpd, just above the 10 cpd threshold at which humans are considered legally blind.
“The human visual world is in front and humans move into it,” Martin once wrote. But “the avian world is around and birds move through
A seal’s visual field is more similar to ours but with excellent coverage above its head and poor coverage below, presumably to spot fish silhouetted against the sky. A seal that swims upside down might look relaxed to a human observer, but is actually scanning the seafloor for food.
Looking around, which is inextricable from our experience of vision, is actually an unusual activity, which animals do only when they have restricted visual fields and narrow acute zones.
Coenosia attenuata.
Mantis shrimps throw punches like humans throw opinions—frequently, aggressively, and without provocation.
You might think that these pollinators evolved eyes that see flowers well, but that’s not what happened. Their style of trichromacy evolved hundreds of millions of years before the first flowers appeared, so the latter must have evolved to suit the former. Flowers evolved colors that ideally tickle insect eyes.
Beauty is not only in the eye of the beholder. It arises because of that eye.
I noted at the start of this chapter that color is fundamentally subjective. The photoreceptors in our retinas detect different wavelengths of light, while our brains use those signals to construct the sensation of color. The former process is easy to study; the latter is extremely difficult.
Nociception says, “Get away.” Pain says, “…and don’t go back.”
property, filling plants with their vibrational songs. Between treehoppers, leafhoppers, cicadas, crickets, katydids, and more, Cocroft estimates that around 200,000 species of insects communicate through surface vibrations. Their songs aren’t normally audible, and so most people are completely unaware that they exist.
It is surprisingly easy to tap into that extra richness, even without a laser vibrometer. In 1949, three decades before such instruments were invented, a pioneering Swedish entomologist named Frej Ossiannilsson heard the vibrations of leafhoppers by putting them on grass blades, sticking the blades in test tubes, and holding the tubes to his ear. As a trained violinist, he transcribed what he heard in musical notation.
Imagine how much quieter the ground is now without all those hooves and paws. Six continents that once would have thundered with the footsteps of titans now reverberate with sparse gurgles.
In a very real way, the spider thinks with its web. Tuning the silk is like tuning its own mind.
An owl’s ears, however, are uniquely asymmetric, with the left being higher than the right. If you think of an owl’s face as a clock, its left ear opens at two o’clock and its right ear at eight o’clock.
He could listen to whales singing in Ireland with a microphone situated off Bermuda. “I just thought: Roger was right,” he says. “It is physically possible to detect a blue whale singing across an ocean basin.”
That night, she had a dream in which she was visited by a group of elephants. The matriarch said, “We did not reveal this to you so you would tell other people.” Payne interpreted this not as a call for secrecy but as an invitation: We revealed it to you not to make you famous among people, but to give you access to us.
The U.S. Navy started training dolphins in the 1960s to rescue lost divers, find sunken equipment, and detect buried mines. In the 1970s, it invested heavily in echolocation research, not to understand how the dolphins themselves perceived the world but to improve military sonar by reverse-engineering the animals’ superior capabilities.
When the time comes for birds to migrate, they become visibly restless. Even in captivity, they’ll hop, flit, and flutter. These frantic movements are known as Zugunruhe—a German word that means “migration anxiety.”
A striking pattern emerged: On days with the most intense solar storms, gray whales were four times more likely to beach themselves.[*5]
At the time of writing, magnetoreception remains the only sense without a known sensor. Magnetoreceptors are “the holy grail of sensory biology,” Eric Warrant tells me. “There may even be a Nobel Prize in finding them.”
Magnetic fields are also deeply counterintuitive. As the Insane Clown Posse famously noted, “Fuckin’ magnets, how do they work?”
Animals never use a single sense exclusively. “They use every damn piece of information they can get their hands on,” Warrant tells me. “They are multisensory in every possible way.”
We now live in the Anthropocene—a geological epoch defined and dominated by the deeds of our species. We
In 2016, when the team updated their atlas, they found that the problem was even worse. By then, around 83 percent of people—and more than 99 percent of Americans and Europeans—were living under light-polluted skies. Every year, the proportion of the planet covered by artificial light gets 2 percent bigger and 2 percent brighter. A luminous fog now smothers a quarter of Earth’s surface and is thick enough in many places to blot out the stars. Over a third of humanity, and almost 80 percent of North Americans, can no longer see the Milky Way.
Sensory pollution is the pollution of disconnection. It detaches us from the cosmos. It drowns out the stimuli that link animals to their surroundings and to each other.
We have to save the quiet, and preserve the dark.
Every year, on September 11, the sky above New York City is pierced by two columns of intense blue light. This annual art installation, known as Tribute in Light, commemorates the terrorist attacks of 2001, with the ascending beams standing in for the fallen Twin Towers. Each is produced by 44 xenon bulbs with 7,000-watt intensities. Their light can be seen from 60 miles away. From closer up, onlookers often notice small flecks, dancing amid the beams like gentle flurries of snow. Those flecks are birds. Thousands of them.
And by analyzing radar images, Benjamin van Doren showed that the Tribute in Light, across seven nights of operation, waylaid around 1.1 million birds. The beams reach so high that even at altitudes of several miles, passing birds are drawn into them. Warblers and other small species congregate within the light at densities up to 150 times their normal levels. They circle slowly, as if trapped within an incorporeal cage.
Over a century later, environmental scientist Travis Longcore and his colleagues calculated that almost 7 million birds a year die in the United States and Canada after flying into communication towers.[*2]
It’s a sunny April morning in Boulder, Colorado, and I’ve hiked up to a rocky hillside, about 6,000 feet above sea level. The world feels wider here, not just because of the panoramic view over conifer forests but also because it is blissfully quiet. Away from urban ruckus, quieter sounds are unmasked and become audible over greater distances. On the hillside, a chipmunk is rustling. Grasshoppers snap their wings together as they fly. A woodpecker pounds its beak against a nearby trunk. Wind rushes past. The longer I sit, the more I seem to hear. Two men puncture the tranquility. I can’t see
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Equating wilderness with otherworldly magnificence treats it as something remote, accessible only to those with the privilege to travel and explore. It imagines that nature is something separate from humanity rather than something we exist within.
The majesty of nature is not restricted to canyons and mountains. It can be found in the wilds of perception—the sensory spaces that lie outside our Umwelt and within those of other animals. To perceive the world through other senses is to find splendor in familiarity, and the sacred in the mundane.
Wonders exist in a backyard garden, where bees take the measure of a flower’s electric fields, leafhoppers send vibrational melodies through the stems of plants, and birds behold the hidden palettes of rurples and grurples.
Wilderness is not distant. We are continually immersed in it. It is there for us to imagine, to savor, and to protect.
