Name: An Immense World
Rating: 4.5 (96 reviews)
Author: Ed Yong

What’s in it for me? Discover a world hidden to human senses.

If asked to name the senses, most of us might answer with the common five: touch, taste, sight, hearing, and smell. These are the senses most commonly linked to being human. But frankly, compared to the rest of the animal kingdom, these five senses barely scratch the surface.

Maybe you’ve heard of birds using the earth’s magnetic field – a sense called magnetoreception – to migrate for the winter. But were you aware that sea turtles and spiny lobsters also use this sense?

And you’ve almost definitely heard of electric eels – but did you know they can actually generate enough voltage to kill a horse?

But let’s not give all the credit to animals. Perhaps you’ve heard of dolphins and bats using echolocation – did you know humans are actually capable of it too?

These are just some of the amazing sensory abilities we’ll explore in this Blink to Ed Yong’s An Immense World. You’ll catch a glimpse of a world yet unknown to humans and discover entirely new ways of making sense of the realms around us.

As we journey through the world of moles that build mental maps using touch, beetles that hunt fires, and fish that generate electric fields, keep your mind (and senses!) open. You just might find yourself thinking – and interacting with your environment – in new ways.

Seeing the world: Color and echoes

Most of human society is built largely around our sense of sight. How we dress, how we get around, how we consume information . . . the list is endless. And, to be fair, humans do have a sharp sense of sight – at least compared to much of the animal world. Humans are trichromats, which means we have three different cones in our eyes that specialize in detecting certain wavelengths of light.

By contrast, dogs and horses only have two. Dogs mostly see shades of gray, yellow, and blue as a result. Many “color-blind” people are also missing one of the three cones humans usually have, and so they see a smaller range of colors. Those of us who use three cones to see color can get an idea of how dichromats see the world using picture editing software. But we can’t imagine what seeing with four cones would be like.

Animals with more than three cones perceive more colors than we can even comprehend. But they can’t compare those colors, which is how sighted humans build an understanding of what the world looks like around them.

Instead, for animals whose brains don’t compare colors, different wavelengths of light merely spark instinctive responses. Daphnia water fleas only see flashes of color, not full landscapes. An ultraviolet light indicates sunshine, so they swim away. They swim toward the colors green and yellow because those wavelengths indicate food. These fleas interpret wavelengths of light as just another stimulus prompting their instinctual behaviors. They simply don’t experience the sense of sight the same way we do.

Another way of “seeing” the world involves a different sense: echolocation. Animals like bats and dolphins use echolocation to build visual pictures of the world around them. They produce pulses of ultrasonic sound, then listen to the echoes returned from objects around them. They vary the length and frequency of these sounds to build clear pictures of their surroundings.

In fact, bats are so good at this that they can snatch flying insects out of the air and navigate through a maze of hanging chains. Dolphins can recognize two-dimensional pictures of items they’ve previously investigated using sonar.

But this incredible ability isn’t just limited to the animals around us – humans can learn to echolocate too.

Daniel Kish had his eyes removed at the age of 13 months in response to a particularly aggressive form of eye cancer. As he grew up, he started exploring the world using tongue clicks. It took him awhile to be able to put words to what he was doing – echolocating. Now, after decades of practice, Kish can take a walk around the block and tell where houses end, where a yard is versus a driveway, and where trees stand. He ducks to avoid branches of trees overhanging the sidewalk – branches he senses using echolocation.

By watching dolphins and bats echolocate, we can determine a lot about how the sense works and what its limitations are. But Kish can tell us how it works for him. Because his sonar is lower in frequency than bats’, the resolution of what he senses is a little blurry. Edges aren’t crisp, and objects in front of large backgrounds – like a person standing right against a wall, or a small object on the ground – can be hard to sense. So he mostly defines objects by their density and texture when using echolocation.

Smelly but tasty

Name an animal that excels at smelling.

Which animal did you pick? A dog? An elephant? Probably not an ant. But while ants are tiny, they actually have an incredibly sensitive sense of smell. They leave scent trails for themselves and others to indicate where they’ve found food, to identify each other as members of the same anthill, and to summon their colony members to overwhelm prey with their numbers.

A touch of vibration

Speaking of food, we humans tend to identify our food first by sight, and then by smell and taste. But star-nosed moles identify their food using touch. The fleshy protuberances on their noses – eleven points that resemble a star – are extremely sensitive to touch. The mole presses this star against its tunnel walls and floor at a rate of dozens of presses per second. This probably helps the mole build a mental map of its surroundings, like how we might use our hands to build such an image in place of sight.

Of course, we can’t know for sure how the mole interprets what it feels with its nose because we don’t speak the same language and can’t read its mind. But we can tell that the mole uses its nose to distinguish textures at the very least. Star-nosed moles will eat dead pieces of earthworms. But they ignore pieces of silicon and rubber, even if they’re similar in size.

Unusual (and unusually sensitive) senses

Although humans sense infrared radiation to a certain extent – we feel it as heat, like from a fireplace or a hot oven – we definitely don’t have the finely tuned sense of it that melanophila beetles do.

Our ability to sense infrared radiation dies off once we get far enough away from the source – which could be anywhere from a few feet to a few hundred feet if the source is big enough, like a bonfire or forest fire.

Key ideas in An Immense World