AN IMMENSE WORLD
How Animal Senses Reveal the Hidden Realms Around Us
By Ed Yong
Illustrated. 449 pages. Random House. $30.
A dolphin that echolocates a human in water can perceive not only the human’s outer shape but also what’s inside, including skeleton and lungs. Tree frog embryos — ensconced inside their unhatched eggs — can detect the vibrations of an attacking predator and release an enzyme from their faces that dissolves the casings that house them, allowing them to exit and escape.
That I found myself surprised at so many moments while reading “An Immense World,” Ed Yong’s new book about animal senses, speaks to his exceptional gifts as a storyteller — though perhaps it also says something regrettable about me. I was marveling at those details because I found them weird; but it turns out, if I try to expand my perspective just a bit, they aren’t so weird after all. One of Yong’s themes is that much of what we think of as “extrasensory” is “simply sensory.” A term like “ultrasound” is “an anthropocentric affectation.” The upper frequency limit for the average human ear may be a measly 20 kilohertz, but most mammals can hear well into the ultrasound range.
Yong offers these facts in a generous spirit, clearly aware that part of what will enthrall readers is discovering just how few of these facts many of us have known. I would have called the book “illuminating,” but Yong made me realize how much bias is baked into an adjective like this; humans, as a species, are “so relentlessly visual” that light for us has “come to symbolize safety, progress, knowledge, hope and good” — and so we have illuminated the planet to make it a more comfortable place for us, while making it less inhabitable for others. Artificial lights have been a fatal attraction for sea turtle hatchlings, migrating songbirds and some insects, steering them toward predators or disorienting them to the point of exhaustion.
Understanding this requires us to stretch the boundaries of our own “unique sensory bubble” in order to glean what we can of how other species experience their surroundings. Yong’s book is funny and elegantly written, mercifully restrained when it comes to jargon, though he does introduce a helpful German word that he uses throughout: Umwelt. It means “environment,” but a little more than a century ago the Baltic German zoologist Jakob von Uexküll used it to refer more specifically to that sensory bubble — an animal’s perceptual world.
The animals in Yong’s book are mostly nonhuman, but scientists are necessarily part of his story too. “A scientist’s explanations about other animals are dictated by the data she collects, which are influenced by the questions she asks, which are steered by her imagination, which is delimited by her senses,” Yong writes. The human Umwelt will necessarily shape how we apprehend other Umwelten. “An Immense World” inevitably refers to the philosopher Thomas Nagel’s foundational essay on this struggle, “What Is It Like to Be a Bat?”
But some humans might be more open-minded than others. A number of the sensory biologists Yong meets are perceptually divergent, seeing color differently or having difficulty remembering familiar faces: “Perhaps people who experience the world in ways that are considered atypical,” he writes, “have an intuitive feeling for the limits of typicality.”
“An Immense World” is organized by stimuli and their corresponding senses, beginning with smell and taste and extending to the ability of some animals — birds, bumblebees — to detect Earth’s magnetic field. When it comes to sight, there’s a trade-off between sensitivity and resolution; humans tend to have extraordinary visual acuity during the day but have a much harder time seeing at night, while animals with better night vision don’t register the crisp images at a distance that we do. “Senses always come at a cost,” Yong writes. “No animal can sense everything well.” The world inundates us with stimuli. Registering some of it is taxing enough; fully processing the continuous deluge of it would be overwhelming.
Still, an animal will use the various senses it has at its disposal to make sense of the world around it. A mosquito is attracted to the heat of warm-blooded hosts, but it will only attack if it first smells carbon dioxide — the sensation of heat without carbon dioxide isn’t a meal for a mosquito but a sign of possible danger. A researcher tells Yong that protecting humans from mosquitoes is a complicated undertaking, requiring her to consider multiple senses at once; the tiny insect has “a plan B at every point.”
Exchanges like this are an outlier in the book. Yong isn’t all that interested in the familiar question of how to exploit the senses of animals for human benefit; he wants us to try to understand how animals experience the world so that we can understand how animals experience the world. A mouse’s whiskers are for whisking, allowing it to scan the space around its head; what looks like a fly’s chaotic flight path turns out to reflect the finely attuned thermometers of its antennae, which steer it toward more comfortable temperatures. “Animals are not just stand-ins for humans or fodder for brainstorming sessions,” Yong writes. “They have worth in themselves.”
If there is a benefit to trying to imagine ourselves into the experiences of others, maybe it lies in the enormous difficulty of doing so; the limits of every species’ sensory bubble should serve as a reminder that each one of us has purchase on only a sliver of reality. Yong’s previous book, “I Contain Multitudes,” was an exploration of microbes and microbiomes; his writing for The Atlantic on the Covid-19 pandemic has frequently shown how the response to the crisis has been limited by our assumptions about the world and our place in it. Yong would like us to think more expansively — something that humans are, it turns out, equipped to do.
Thinking expansively would help us realize that nature’s true wonders aren’t limited to a remote wilderness or other sublime landscape — what Yong calls “otherworldly magnificence.” There is as much grandeur in the soil of a backyard garden as there is in the canyons of Zion. Recognizing the breadth of this immense world should spur in us a sense of humility. We just need to get over ourselves first.