Imagine you are at the seaside. Sunlight is hitting the surface of the ocean. Some wavelengths of light pass into the water, while others bounce off it, scattering in all directions. A tiny fraction of reflected light happens to reach receptors at the back of your eyeball, triggering electrical impulses that cause your brain to register the colour turquoise. Other rays from the sun fall directly on your skin, where receptors detect a sensation of warmth. A pulse of pressurised air from the lungs of a gull flying overhead sets up a wave of ripples in the air around it. As the wave travels outward, it bends sensitive hair cells in your inner ear, triggering an electrical signal creating the experience of sound.
We assume the information our senses feed us is objective — of course we do, because what else do we have to go on? There is something almost vertiginous, then, about Ed Yong’s new book, An Immense World: How Animal Senses Reveal the Hidden Realms Around Us, which confronts exactly how we perceive what we perceive. “Light is just electromagnetic radiation,” he says. “Sound is just waves of pressure. Smells are just small molecules. It’s not obvious that we should be able to detect any of these,” let alone that they should produce the particular subjective experiences that they do.
Your experience of a beach — the turquoise sea, the warmth of the sun, the screeching gull — isn’t what the beach is. The “real” beach is giving off all sorts of stimuli, only some of which a human brain uses to form a mental representation of its surroundings. There are many, many more stimuli that we cannot sense or even imagine sensing. But other species can.
Take the seabirds on the beach, for instance. Many seabird species are finely attuned to the scent of chemicals that give away the presence of the krill they eat, meaning that far from a flat, featureless expanse, the ocean’s surface has “a secret topography” of “odorous mountains and unscented valleys… invisible to the eye but evident to the nose”. Others are able to sense the Earth’s magnetic field, which guides them during migrations. And almost all birds can discriminate between “millions” of colours that humans are unable to imagine — to them, we are colourblind.
Some of the senses Yong details are delightfully surreal. A dolphin is effectively a “living medical scanner”: echolocation allows them to “perceive your lungs and skeleton… shrapnel in war veterans and foetuses in pregnant women”. Incredibly, beaked whales, which also echolocate, have “a strange assortment of crests, ridges, and bumps” on their skulls, which might be a form of “internal antlers” that could allow them to signal to others while retaining a sleek, hydrodynamic form.
What these alien senses might feel like, we can only guess. Philosophers have long grappled with this problem of subjectivity. Thomas Nagel, in his 1974 essay What Is It Like to Be A Bat?, argued that it is impossible to capture the experience of one sense by analogy to another: for example, “red is like the sound of a trumpet”. “That should be clear to anyone who has both heard a trumpet and seen red,” he wrote. It may be tempting to talk about dolphins “seeing” the inside of each others’ bodies, but in reality, it’s possible that what they experience via their sonar sense may be so different that trying to imagine it as a kind of “seeing” is as futile as describing the colour red in terms of its musical qualities.
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