Umwelt

Back in 1974, the philosopher Thomas Nagel wrote an article titled “What is it like to be a bat?”. Back then, he was probing the question of consciousness.

 

The answer fifty years later is that we still don’t know. We’ve learned a lot about bats since then. We’ve also learned a lot about various creatures large and small, and scientists now realize we don’t know what it’s like to be a bat or a cat, an owl or a fowl, because we humans rely mostly on one of our five senses: vision. Our vision is acute and we’re good at distinguishing colors. Some birds have better vision than us, but most creatures of the animal kingdom do not. This is the subject of Ed Yong’s marvelous new book, An Immense World, subtitled “How animal senses reveal the hidden realms around us”.

 

While vision is the primary sense utilized by humans as we go through our motions in everyday life, we also smell, taste, hear, and touch. But for a mole in a hole, vision isn’t important at all. Some moles are blind, and those that are not have poor vision. But moles have other senses enhanced. The star-nosed mole, a remarkably strange creature, has a snout covered with sensitive mechanoreceptors that relays detailed information to its brain of what it encounters. How the mole decides what is food and what is not, just from the sensation of touch, is so quick that it can only be captured with high-speed cameras.

 

We have an anthropocentric view of our five senses. Thus, we think that other creatures use their senses the way we do and pay attention to the same things that catch our attention. This is almost never the case! I had long thought (because I read it somewhere) that the zebra has stripes so it can camouflage itself in the savanna, especially in a group setting, and thus confuse lions. Turns out lions have rather poor vision and do not notice the stripes that we think are significant. The zebra might look just like a horse or a donkey to a lion. Why the stripes? Turns out that the stripes are to ward off bloodsucking insects that carry disease like the tsetse fly.

 

We also artificially classify the senses based on where our organs of perception are located. The eye sees. The nose smells. The tongue tastes. The ear hears. The skin touches. Depending on the stimulus, one or more of our senses may pick it up. We’re familiar with the close relationship between smell and taste. When you have a bad cold and can’t smell much, food tastes much blander. Or you pick up something from one sense and shift to another. You hear a noise, and you turn your head so you can see where it comes from. How we perceive the world as humans is based on the particular sensory organs we have and use. Ed Yong calls this the Umwelt – a word first used by a zoologist Jakob von Uexkull. Here’s how he describes the feeling of it.

 

Earth teems with sights and textures, sounds and vibrations, smells and tastes, electric and magnetic fields. But every animal can only tap into a small fraction of reality’s fullness. Each is enclosed within its own unique sensory bubble [the Umwelt], perceiving but a tiny sliver of an immense world… Uexkull didn’t use [Umwelt] simply to refer to an animal’s surroundings. Instead, an Umwelt is specifically the part of those surroundings that an animal can sense and experience – its perceptual world... Creatures could be standing in the same physical space and have completely different Umwelten.

 

Yong’s book is a marvelous exploration into the Umwelten of different creatures. All I can say after reading his many examples is that evolution has tuned the remarkable sense-abilities of different creatures based on their surrounding environment and ecology. Yong is also one of the most engaging science writers I’ve had the privilege of reading. His book is a page-turner and you’ll want to read every footnote. Nature is strange and fascinating. I’m sure I would have become a biologist had I read An Immense World at an early age or seen the Planet Earth series. Living creatures are amazing! I’m making up for it as a chemist by studying the origin of life.

 

Chapter 1 of Yong’s book is titled “Leaking Sacks of Chemicals”. By grouping smell and taste together, he emphasizes the uniqueness of these two senses – they sense chemical substances at the individual molecule level. Yong writes: “Many living things can sense light. Some can respond to sound. A select few can detect electric and magnetic fields. But every thing, perhaps without exception, can detect chemicals. Even a bacterium, which consists of just one cell, can find food and avoid danger by picking up on molecular clues from the outside world. Bacteria can also release their own chemical signals to communicate with each other…” I’d call this the First Sense! How appropriate that it is chemical in nature!

 

I learned about the exquisite nature of the dog’s nose. It’s a marvel! (You’ll have to read Yong’s book to find out more.) And it turns out the human nose is also quite impressive and can be trained. Those books that say our sense of smell is poor in the animal kingdom are very wrong, says Yong. And he provides examples to back up his claim. It’s tough to study taste and smell. Yong writes: “Scientists who work on vision and hearing have it comparatively easy. Light and sound waves can be defined by clear and measurable properties like brightness and wavelength, or loudness and frequency… Such predictability simply doesn’t exist in the realm of smells. To classify them, scientists use subjective concepts like intensity and pleasantness, which can only be measured by asking people. Even worse, there are no good ways of predicting what a molecule smells like – or even if it smells at all – from its chemical structure.” Sounds like a challenge for chemists!

 

I learned about moths. I learned about ants. I learned about elephants. I learned about birds – vultures, migrating seabirds, homing pigeons. I learned about snake tongues. Then I learned that bees and flies and wasps have their taste sensors on their feet and legs. Who would have thought? I learned that the catfish probably has the best sense of taste in the animal kingdom: “They have taste buds spread all over their scale-free bodies, from the tips of their whisker-like barbels to their tails. There’s hardly a place you can touch a catfish without brushing thousands of taste buds. If you lick one of them, you’ll both simultaneously taste each other!”

 

And that was just the first chapter. I could probably write a blog post on each chapter. I might at some point when I go back and re-read the book. There are so many nuggets I’d love to explore further, and Yong provides an extensive bibliography to do so. I’ve already started on one of the books he cites, and have several others on my to-read list. I borrowed An Immense World from the library. But I know I’ll be reading it again so I’ll be purchasing my own copy. It’s that good!

 

P.S. Here’s my blog post on Yong’s previous book.