Ed Yong begins An Immense World with an interesting fable. He imagines a room with an elephant, a robin, an owl, a bat, a rattlesnake, a spider, a mosquito, a bumblebee, and a human. He explains that each creature experiences the room in a different way. The human, Rebecca, uses her eyes until it becomes too dark to see. The owl, of course, can see very well in the dark. The snake detects the trail of the mouse with its tongue. The mosquito smells the human. Rebecca hears the robin but misses the high-frequency parts of its call. Each creature uses a different sense to gather information about its environment.
Yong tells us that this sensory bubble is called an Umwelt, a German term referring to an animal’s perceptual world: everything it can sense and experience. Humans tend to be dominated by sight. Our dogs are dominated by smell. Other animals are dominated by an amazing range of senses, including vibrations and electric and magnetic fields. Their experiences of the world are profoundly different from ours. Yong mentions that if you don’t let your dog stop and smell its world on your walk, you are depriving it of its major source of information, its Umwelt.
Each chapter in An Immense World is devoted to a different sense and how it is experienced by various animals. The first chapter is devoted to smells. Yong meets Alexandra Horowitz who is an expert on dog olfaction. The way a dog smells is completely unlike our own way of smelling: they have a “more extensive epithelium, dozens of times more neurons in that epithelium, almost twice as many of kinds olfactory receptors, and a relatively larger olfactory bulb” than humans; in short, completely more powerful. Elephant senses are also dominated by smells. They can smell danger and know one another by smell. It was recently reported that they also know one another by name.
Subsequent chapters deal with light and vision, color, pain, heat, contact and flow, vibrations, sound, echoes, electric fields, and magnetic fields. Yong interviews experts who have spent their careers trying to figure out how animals use each of these senses to navigate the world. Perhaps one of the most mysterious and still little understood is the ability of migrating birds to sense the magnetic field of the earth to help them find their way between their winter and summer territories.
We also learn that birds sing far more complex songs than we ever hear. The sounds they produce are so fast that they exceed our ability to detect them. But other birds hear them all. An Immense World is filled with utterly amazing stories about the work of researchers and the amazing senses they have uncovered and are still trying to fully understand.