An Immense World summary

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.