An Immense World

All too often we think of the looming climate crisis mainly as a threat to humanity, without appreciating the harms it poses to other glories of creation.  We may see, hear, and smell the beauties of the world around us, but we have little idea of how other animals are sensing and perceiving the world we share.  Ed Yong’s An Immense World vividly brings those realities to us.

Yong, an accomplished science writer on the staff of The Atlantic, has interviewed and read the work of a wide array of scientists who in the last few decades have conducted inventive experiments to better understand how other animals sense and perceive the world.  Much of this work is relatively recent because, as Yong recounts early in the book, humans, including many early scientists, once assumed that our five senses represented the pinnacle of animal sensory abilities, and that other animals’ senses were best understood in reference to our own.  Scientists now know that animals’ senses are often better than our own, and that many animals can sense things in the environment about which we are oblivious.  Scientists now understand that each species exists in its own sensory bubble.  Individuals in a species can sense things in the environment that are important to their survival – food, predators, potential mates – but those individuals are blissfully unaware of the rest of the environment.  An early-twentieth-century German scientist chose to use the word, umweld, which means “environment,” to more specifically mean the environment that a species can sense.  Humans’ umweld is the things we can smell, taste, see, hear, and touch, but it does not include those elements of the environment that we cannot sense.  Our umweld may overlap with some parts of other species’ umweld, but each species lives within its own distinct umweld while being senseless of the rest of the world.

Dogs are famous for their masterful abilities to smell, and that’s where Yong begins his impressive march through the impressive sensory abilities of the animal kingdom.  He describes the amazing physiology of dogs’ noses and nostrils that enhance their abilities to smell with great sensitivity and precision.  He then moves to taste, which is a different but related sense that allows animals to detect other chemical signals in their environment.  Mammals, birds, and reptiles taste with tongues, but most insects taste with their feet and legs, so they’re able to know as soon as they land on a potential food item whether to put it in their mouth.

Yong next moves to descriptions of sight, by which animals sense light.  There’s amazing variety in what animals see, including which portions of the light spectrum they can sense, whether they see sharply or not, whether they see best in the day or at night (even when it is incredibly dark), whether they can or cannot sense polarized light, etc.  Humans can only see the spectrum of color between red and violet.  Some animals can sense only a portion of that spectrum, while other animals can sense light in the infrared range or can sense ultraviolet light.  Associated with this variety in what animals can see, there’s an amazing variety in the kinds of eyes animals have and where those eyes are located on their bodies.  A chameleon has two independent eyes, so one can look backward while the other looks forward.  Some scallops have dozens of eyes along the rims (top and bottom) of their shells.

There are several chapters on senses associated with touch, with the first being on pain, “The Unwanted Sense.”  Here is where Yong makes an important distinction between sense and perception, using the example of a human touching a hot pan on the stove.  Our sensory system is such that, if a finger touches that hot pan, the hand and arm will reflexively jerk away well before a signal has gone to the brain to be translated into a perception that a part of the body has experienced pain.  Throughout human history, there has been a wide understanding that animals cannot feel pain, that pain is a perception of which only humans are capable.  Yong describes experiments that scientist have now undertaken to demonstrate that animals not only sense things like heat or pressure that are threatening their well-being; many animals do indeed perceive pain.  I found this chapter on the perception of pain by animals quite moving.

I had a wonderful experience of the difference between sense and perception (not involving pain) recently at the Angry Trout in Grand Marais while eating a salad that included fava beans.  I was holding a bean between the thumb and forefinger of my right hand, appreciating its color and shape before eating it.  When I moved to place the bean in my mouth, it slipped from my fingers.  Reflexively my left hand moved into position at the middle of my abdomen and caught the falling bean.  Immediately afterward I perceived what had happened.  My sensory system had responded to catch the bean before my brain had had a chance to initiate any considered action based on conscious perception.  But when my perception of the event happened, I immediately appreciated what I had learned in An Immense World.

There are several kinds of physical factors that animals can sense, including heat and cold, pressure, the characteristics of a solid surface, and the flow of a fluid (liquid or air) past a body.  Again, there’s an amazing array what animals can sense or perceive and how they put that information to use.  One area where humans excel is in the ability of our fingertips to sense and perceive differences in the texture of a hard surface.  This is what gives blind people the ability to read Braille.  Perhaps the only animal that is better at this kind of tactile sensitivity is sea otters.  With their paws they can distinguish differences in texture of miniscule subtlety.

Another kind of touch in which certain animals, especially insects, excel is the ability to sense vibrations along surfaces.  Sound moves through air or water in three dimensions, so the energy of sound waves dissipates relatively quickly.  Vibrations move along surfaces in only two dimensions, so even small vibrations can travel quite a distance along a solid surface.  Insects and other animals use these vibrations on twigs and leaves to communicate with each other or to detect the presence of food or predators.  The wit in Yong’s writing is evident in his description of a kind of worm in Florida, where “worm grunters” (people who pound stakes into the ground) have learned how to get worms to rise out of the soil to be collected in buckets and used as bait.  Worm grunters thought they were mimicking the sound of rainfall to coax the worms out of the ground, but it turns out that the vibrations made by pounding stakes are similar to vibrations made by digging moles, which feed on the worms.  Worms want to escape the moles, which don’t prey on the surface, but some surface predators have learned to mimic those vibrations.  Yong writes, “Herring gulls and wood turtles do this, as, apparently, do some Floridians.”

Hearing is another sense that detects physical phenomena rather than chemicals or light.  Hearing is a “mechanical” sense, and it can occur at a distance.  All mammals’ ears are pretty similar.  They come in pairs, and they’re always located on the head.  Ears allow a mammal to sense the direction of a sound because the brain instantly calculates the time difference for the sound to reach the ear on either side of the head.  But that only works for mammals sensing sound on the horizontal plane, not from above or below.  Owls, which have exceptional hearing anyhow, are distinct in the location of their ears.  The owl’s face is flat, which helps to gather the sound.  In addition, the owl’s ears are located asymmetrically on the face, very near the eyes.  The ear on one side is higher on the face and on the other side just a bit lower, thus allowing an owl to sense whether a sound is coming from the right or the left as well as from above or below.  Insects, on the other hand, have evolved ears on all sorts of places, like their knees or abdomens, while other insects have no known organs for hearing.

After describing the wonderful diversity in the ways other animals engage in the five sense humans have, Yong describes senses that humans don’t have: echolocation, the ability to sense electrical fields, and the ability to sense magnetic fields.  Bats, dolphins, and certain whales have highly refined abilities to sense by echolocation, an ability that is quite complex.  The screech that bats send for echo location is well over 200 decibels.  Fortunately for us, the screech is at a frequency that is much higher than humans can sense, so we’re not deafened by bats flying around at night.  Yong also writes about a man in his 50s who is an echolocator.  As a baby, he developed a rare eye cancer so one eye had to be removed at seven months of age and the other when he was little a year old.  By the time he was two, though, he had learned on his own to echolocate by making a clicking sound with his tongue.  He now walks with a cane, because echolocation does not provide him enough information about the ground surface to be able to walk safely and confidently, but he perceives an amazing amount of information about the rest of his umweld through echolocation.  When Yong went for a walk with him, he could tell Yong when they were passing a house, whether a car was parked on grass or pavement, and when to duck under a tree branch hanging low over the sidewalk, all by echolocation.

Many animals can gain information about their umwelds by sensing electrical fields.  These include electric fish, which produce their own electric fields.  Their bodies are covered with electroreceptors, so the fish know when bodies or objects that are conductors or insulators pass within their electric fields.  These fish also have fins that make them incredibly agile, so they can stop swimming almost instantly and swim backwards to further investigate a potential meal without creating little eddies by turning around, eddies that could warn the prey of the electric fish’s interest.

Scientists have recently learned that bees, too, can sense electrical fields, even though they don’t generate their own.  The Earth does that for them.  In the world around us, the Earth itself has a negative charge, and the atmosphere has a positive charge.  Because plants are mostly water, and they are intimately connected to the Earth by their roots, they also are negatively charged, even though they extend upward into the atmosphere with its positive charge.  That difference in electrical charge is especially evident – if an animal can sense it – along a plant’s surfaces, especially along the edges of leaves and flower petals.  Scientists have shown, within the past decade, that bees can detect those electrostatic patterns.  Scientists now think that the hairs on bees may serve as electroreceptors, allowing bees to recognize the electrical patterns that exist around plants, thus helping bees know which plants offer food.  Reading of this recent discovery has given me an entirely new vision of the sensing that is happening in our backyard garden as bees come to visit our flowers and other blossoms.

The last sense Yong describes is the ability to use the Earth’s magnetic field to navigate.  Migrating birds do it, as do salmon and sea turtles.  Of all the senses that some animals have, and that humans don’t, this one remains the most mysterious to scientists.  For example, scientists still haven’t identified the receptor(s) or other body parts that animals use to detect magnetic fields.

Yong’s penultimate chapter is about the ways animals combine their senses to know even more about their respective umwelds.  A essential ability, which all animals possess, is the brain’s integrating of sensory information with the brain’s motor commends.  By this processing, an animal knows whether a feeling of touch, for example, has been initiated by another object coming in contact with the animal, or by the animal initiating the movement of one of its limbs to contact another object.  This ability explains why a human can be tickled by another person, but a human cannot tickle him- or herself.

Yong writes with clarity, beauty, and wit about the complex features of animals’ sensory systems.  I’ve sampled here just few of the animals and their senses that he describes.  Nearly every page filled me with wonder at how glorious our world is and at the brilliance of the scientists who are deploy clever methods to gain new insights into their chosen animals’ capabilities and umwelds.  His book is also loaded with footnotes that are not to be ignored; nearly every note provides a fascinating side bit of information on a former set of beliefs about animals, or what animals can do or sense, or the peculiarities of scientific investigations.

An Immense World closes with a chapter on pollution, not the chemical and biological pollutants with which we’re fouling environments, but pollutants like light and sound that are invading the umwelds of our fellow animals, making it more difficult for them employ the senses they need to survive.  We are often more oblivious of this kind of pollution than we are of chemical and biological pollution.  Yong’s book gives us powerful insights into the magnificence of the world around us, a magnificence we cannot sense but which we can perceive thanks to the work of scientists who are learning how other animals sense and perceive their umwelds, worlds of which we are otherwise unaware and completely senseless.  The climate crisis threatens so much more than humanity; it threatens marvels of creation that can fill us with awe and wonder. 

An Immense World: How Animal Sense Reveal Hidden Realms Around Us. Ed Yong. New York: Random House, 2022. 449 pp., references & index.