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The human sensory experience is limited. Journey into the world that animals know

Science writer Ed Yong recently won the Carnegie Medal for Excellence for An Immense World, his book about the diversity of perception in the animal world. Originally broadcast June 22, 2022.


Other segments from the episode on February 17, 2023

Fresh Air with Terry Gross, February 17, 2023: Interview with De La Soul; Interview with Ed Yong; Review of Emily



This is FRESH AIR. I'm David Bianculli, professor of television studies at Rowan University, in for Terry Gross. After winning the Pulitzer Prize for his reporting for Atlantic magazine on the first year of the pandemic, science writer Ed Yong shifted his focus. Instead of examining the catastrophes and tragedies caused by COVID, he moved on to a facet of the natural world he hoped would bring some joy to his life and to his readers.

The result is his book, "An Immense World: How Animal Senses Reveal The Hidden Realms Around Us." Last month, it was awarded the Carnegie Medal for Excellence. It's almost like science fiction or the supernatural in that it describes the worlds that animals, birds and insects perceive which humans can't - the sounds, smells, colors, vibrations, echoes and magnetic fields that exist beyond the limits of our senses. As he puts it, every animal, including humans, can only tap into a small fraction of reality's fullness. The book is about the diversity of perception in the animal world and the limits of human perception. Ed Yong spoke with Terry Gross last year.


TERRY GROSS: Ed Yong, welcome back to FRESH AIR.

ED YONG: Hi. Thanks for having me.

GROSS: So your book is about how every animal, including us, is enclosed within its own sensory bubble, as you put it, perceiving but a tiny sliver of an immense world, which leads to the word umwelt, which is a word I'm sure you'll be using. So why don't you describe what it is?

YONG: So umwelt was popularized by a German biologist named Jakob von Uexkull. The word comes from the German for environment, but von Uexkull wasn't using it to mean the physical environment. He meant the sensory environment, the unique set of smells, sights, sounds and textures that each animal has access to and that might be unique to it, its own little bespoke sliver of reality.

So I'll give you an example. Like, humans can see colors ranging from red to violet, but we don't - we aren't able to see the ultraviolet colors that actually most sighted animals can perceive. We can't detect the magnetic field of the earth that songbirds and sea turtles can. We can't detect the ultrasonic frequencies that bats use to navigate around them or that rats and mice use to send messages to each other that we can't hear. So every creature has these sensory limitations and is enclosed in its own particular sensory bubble. And that's what the umwelt is.

GROSS: Where are you now?

YONG: I am in my home in D.C. I am in the recording studio/shoe closet...

GROSS: (Laughter).

YONG: ...Of my bedroom, or as my wife calls it, our shoe-deo (ph).

GROSS: OK, so it's not exactly a rich sensory environment. But if you...

YONG: It is not.

GROSS: If you were one of the animals you were writing about, or insects or birds, what might you perceive in this studio/closet that you can't perceive now?

YONG: So at the start of the book, I do this - exactly this thought experiment, right? I imagine that I'm - a human is sharing a physical space with a bunch of creatures - say, a rattlesnake, an elephant, a mouse, a dog. It's hard to imagine all of those in this shoe closet with me. But if we do, then the rattlesnake, for example, will be able to sense my body heat. Even if I switched off the light in this closet, it would be able to detect my presence from the infrared radiation I was giving off.

A bird in this closet, even though it was surrounded by walls, would be able to detect the magnetic field of the earth and would know which direction to fly if it was time to migrate. A dog - if my own dog, Typo, who's a corgi, was in this room, he'd almost certainly be sniffing around. He'd be picking up the odors that are abounding in the space and that I cannot detect. So each of these creatures - we could all be sharing exactly the same physical space and have a radically different experience of that space. And that's what "An Immense World" is about. It's about going through these adventures, these sensory voyages, by considering the umwelt of other animals.

GROSS: Let's talk a little bit about vision. You mentioned ultraviolet light, which we cannot see. All the colors we see are based on three colors - blue, yellow and red, although I really don't understand exactly...

YONG: Red, green and blue.

GROSS: Red, green and blue - wait, I thought green was blue and yellow.

YONG: So you're thinking about primary colors, like with paints. For light, it's different. So with light, it's based on red, green and blue.

GROSS: No kidding. Really? Oh, I didn't know that. OK. So we see red, green and blue.

YONG: Yes, we have three kinds of color-sensitive cells in our eyes that are most sensitive to red, green and blue.

GROSS: So what are we missing? Like, for insects that can see - or butterflies, I guess, that can see ultraviolet light - what are we missing, for instance, in flowers, which are beautiful enough with what we can see, but what are we missing?

YONG: So flowers absolutely are extraordinarily beautiful. But if you had the ultraviolet vision that a bee has, you'll be able to see patterns on those flowers that we can't see. So a sunflower, for example, far from looking just a matte uniform yellow, would have a stark ultraviolet bull's-eye at its center. A lot of flowers have these ultraviolet shapes like arrows and bull's-eyes to guide insects towards the pollen at their center. Some predators that eat pollinating insects, like crab spiders, blend in when - blend in against the flowers to our eyes, but really stand out when viewed in ultraviolet. And that acts as a lure to insects. It draws them in towards the waiting spider.

One of my favorite things about the relationship between insect vision and flowers is that if you took all the colors in all the flowers that were out there and you asked what kind of eye, what kind of color vision is best at discriminating between these colors, what you get is an eye that's basically almost what a bee has, an eye that is maximally sensitive to blue, green and ultraviolet. And you might think then that the bee eye has evolved to see the colors of flowers really well. And that's exactly the opposite of what happened, because the bee eye came first. The flowers evolved later. And so the colors of flowers have evolved to ideally tickle the eyes of bees.

And I think that's a truly wondrous result. It means that beauty as we know it, is not only in the eye of the beholder. It arises because of that eye. Eyes, in viewing nature's palettes, also affect its paintings.

GROSS: Oh, it's really form follows function.

YONG: Yes. Right.

GROSS: So what exactly is UV light? I mean, we know it's used to, like, sanitize things, and, you know, like my electric toothbrush has a UV light in the little cleanser unit. But in terms of vision, like, what is it and why can't we usually see it? Like, the UV light in my toothbrush thing, when I turn it on to clean the toothbrush, I see blue. Maybe that's just a blue lightbulb. I don't know.

YONG: Yeah. Right. That's the blue part of the light that you can see. So our - we can see light ranging from red to violet, right? It's the classic rainbow of colors that we can perceive. Ultraviolet - literally beyond violet - exists beyond the violet end. It's just off its edge. Now, there's a huge range of UV light that includes the stuff that causes sunburn and that, you know, we use to sanitize our world. But there's also a section of it near UV that exists quite close to that violet that we can see that effectively paints nature. You know, it's there in flowers, like we've said. It's there on the feathers of birds. And most other animals that can see color can see that UV. We didn't used to think that. We used to think that it was special, that seeing ultraviolet was rare. And that, I think, reflects how much the limits of our own senses affect our view of the world.

We think of things that have different umwelt, that see differently to us as being extraordinary, whereas, in fact, often they are very typical. So, you know, many - most birds can see ultraviolet; most insects can do it. A lot of other mammals can do it. We're actually quite weird in not being able to see ultraviolet. For a long time, scientists used to think that ultraviolet was a sort of secret communication channel that animals used to send coded, like, hidden messages that other creatures could not see. Sometimes that is the case.

There are, for example, fish that look completely uniform yellow. But if you look at them through ultraviolet, you see that they have, like, distinct patterns on their faces, almost like running mascara. But in the main, those messages aren't secret because most animals can actually see them. Ultraviolet abounds in the world around us, and there's just a ton of stuff that we're missing. You know, there are loads of birds, for example, including common backyard birds, where we think the males and females look exactly the same, but they all look very different to each other because they can see the ultraviolet patterns that distinguish the sexes.

BIANCULLI: Science writer Ed Yong speaking to Terry Gross last year. More after a break. This is FRESH AIR.


BIANCULLI: This is FRESH AIR. Let's get back to Terry's 2022 interview with science writer Ed Yong. His latest book, "An Immense World: How Animal Senses Reveal The Hidden Realms Around Us," won the Carnegie Medal for Excellence last month.


GROSS: Let's talk about echolocation. Why don't you explain what it is?

YONG: Echolocation is a very advanced form of hearing that a lot of animals like bats and dolphins use to perceive the world around them. So they make high-pitched ultrasonic calls beyond the range of human hearing. And they listen out for the echoes of those calls after they've rebounded off objects around the animal. And by listening for those echoes and passing those echoes, they get a sense of the world around them. A bat in complete darkness can find, track and swoop upon a flying insect. It can navigate through the darkness of a cave. It can wend its way around obstacles, all by using this incredibly sophisticated type of hearing.

GROSS: Can we compare the bats' echolocation with an animal that is really, really different, dolphins? Because they use echolocation, too. They're different in terms of the environment they live in, their size, their needs. So could you compare them?

YONG: Yes. Bats and dolphins are the two masters of echolocation in the animal kingdom. And in some ways, they use it to similar purposes. But the difference between them is mostly because dolphins are echolocating in the water. Their calls travel much further. And so for them, echolocation is a much longer range sense than it is for bats. A bat can only really detect a small moth within several feet in front of it. A dolphin's echolocation can extend much, much further. And that allows dolphins, for example, to use echolocation to coordinate their movements, to coordinate their hunting strategies over the distance of an entire pod.

Dolphins can also use echolocation kind of like a medical scanner. They can detect hard surfaces that exist inside other animals. You know, a dolphin echolocating on a human could likely see your skeleton, could likely see your lungs. Dolphins can, through echolocation, detect the swim bladders inside the fish that they hunt. They can probably tell the difference between different kinds of prey by the shape of their swim bladders. So they have this incredible see-through ability, but except it's not really to do with vision, right? It's to do with sound.

GROSS: So I have a cat. And a really interesting thing I learned about cats is that they have muscles in their bellies that sense vibration. Can you elaborate on that?

YONG: Right. So many animals have vibration-sensitive cells in their organs of touch. So, you know, I have them in my fingertips, for example. It seems that cats have that on their bellies. And one scientist I spoke to, you know, had this hypothesis. Like, if a cat is laying down in a crouch, you know, is it also sensing the vibrations caused by possible prey, you know? When we see a lion watching a herd of antelope in the distance, is it also getting information through the crouch about the footsteps of those prey?

Now, I want to be very clear. We don't know the answer to that question. And it might be entirely far-fetched speculation. I write about it in the book specifically because I think it's the type of question we should be asking because a lot of people, including scientists who work on the senses, neglect the world of vibrations, the world of seismic tremors that course through the ground and surfaces along us. You know, we care when those vibrations move through the air. We call them sounds. But when they move through surfaces, we tend to ignore them. Except a huge number of animals - scorpions, moles, elephants - many insects seem to pay attention to that vibrational world. And I think if you really start thinking about it and looking at it, you know, you learn incredible things about nature that you might otherwise have missed.

GROSS: I really like the way you end the book. And you write about how most people think of, you know, the majesty of nature as being like canyons and mountains. But you write, 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. Can you talk about that realization?

YONG: Yeah. This speaks to my earlier point that if you start thinking about the umwelt of other animals, you understand that nature's magnificence is all around us. It's in our backyards. It's in our gardens. You know, it's in the bodies of some of the most familiar creatures around us - my dog, the pigeons on the street. I think that if we think of nature as something remote and distant, you know, accessible only to someone who can go to a national park, we lose the impetus to savor and to protect it. I think if you understand instead that nature is everywhere, that you can go - I can go on an adventure just by thinking about the sensory world of the sparrow that sits on the house opposite me, I think then nature feels like something close to me, close to my heart and close to my life. And I feel like if that's the case, people will be more motivated to try and protect it.

You know, protecting nature isn't just about, like, saving whales or pandas or what have you. It's about protecting even things that are close to us. And - because each of those things has a unique way of experiencing the world that is worth learning about, worth cherishing and worth protecting.

GROSS: Ed Yong, it's been a pleasure to have you back on the show. Thank you so much.

YONG: Thanks, Terry. Always a pleasure talking to you.

BIANCULLI: Pulitzer Prize-winning science writer Ed Yong speaking to Terry Gross last year. His latest book is "An Immense World: How Animal Senses Reveal The Hidden Realms Around Us." Coming up, film critic Justin Chang reviews Emily, the new film dramatizing the life of Emily Bronte before she wrote Wuthering Heights. This is FRESH AIR.


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