What amazing abilities do animals possess that humans can’t even imagine? How and why do their senses work differently than ours?
Ed Yong’s An Immense World: How Animal Senses Reveal the Hidden Realms Around Us explores the fascinating ways different species perceive reality through their unique senses. From dogs that can smell the past to fish that navigate by electricity, the book reveals these remarkable sensory abilities.
Continue reading for an overview of this New York Times best-selling book.
Overview of Ed Yong’s An Immense World
Ed Yong’s An Immense World: How Animal Senses Reveal the Hidden Realms Around Us asserts that every species of animal—humans included—perceives the world differently. While humans tend to think that our way of perceiving the environment is the best and most accurate, many animals have senses that we don’t have, and some have supercharged versions of human senses. In describing the many unique ways animals view the world, Yong contends that the world is far richer and more nuanced than humans’ five senses are capable of perceiving.
Yong argues that because it can be hard for humans to imagine how animals experience the world, human activities can cause severe damage to animals’ senses, often resulting in huge animal die-outs. Human-caused sensory pollution of animals’ environment is contributing to a mass extinction crisis. We thus need to understand how animals perceive the world to save them from extinction.
Yong is a Pulitzer Prize-winning science journalist and author. In addition to An Immense World, he wrote the New York Times bestseller I Contain Multitudes. He has a degree in zoology from Cambridge and a Master of Philosophy in biochemistry from University College London.
We’ll first examine, sense by sense, the many ways in which animals perceive the world differently than humans. Next, we’ll look at how sensory pollution is fatal to animals and their environment—and what we can do to change that.
Part 1: Animals Perceive the World Differently Than Humans
Yong shows that animals perceive the world in myriad ways that humans can’t. Not only do animals use the primary senses—smell, taste, sight, hearing, and touch—in novel ways, they also possess senses that humans don’t have, such as echolocation, electrolocation, and magnetoreception. Animals also experience pain differently than humans.
In addition, Yong says, we all perceive a different slice of the world—no single species can perceive everything in its environment. As a general rule, animals have evolved to perceive only what they most need to function optimally. For example, humans don’t have great night vision because we tend to sleep at night, whereas foxes, which are predominantly nocturnal, have excellent night vision.
We’ll explore how animals perceive the world through each of their senses.
Animals Can Use Their Sense of Smell to Do Many Things Humans Can’t
Yong says that animals can do many things with their sense of smell that humans can’t—they can detect prey, tell individual animals and humans apart, locate hidden objects, create mental “maps,” and much more.
For example, dogs perceive the world primarily through their sense of smell, which is much more advanced than humans’. Humans inhale and exhale a single flow of air for both smelling and breathing. In contrast, dogs’ noses split the airflow into two parts—one for breathing and one for smelling—so when they exhale, the smells they’ve inhaled stay inside their noses.
Because of their heightened sense of smell, dogs can tell identical twins apart by sniff, and can detect all kinds of things that humans can’t, such as tumors, land mines, and missing people. Dogs can even “see into” the past through smell, by detecting who’s been in a room, for example, or even what’s happened there.
Yong also cites elephants as having a highly developed sense of smell. In experiments, they consistently run from clothes worn by the Maasai people, who will sometimes spear elephants, but show little concern when they smell washed clothing or garments worn by the Kamba people, who are not a threat to elephants.
Seabirds such as albatrosses and shearwaters can “map” the vast, featureless ocean by using their sense of smell to detect where there are higher concentrations of dimethyl sulfide, or DMS. DMS is a gas released by plankton when it’s eaten by krill, which is food for seabirds. DMS tells the birds which parts of the ocean contain plentiful food sources.
Animals Can Taste Using Different Body Parts and Are Sensitive to Different Tastes
Taste is a much simpler sense than smell, writes Yong. Whereas there are an immeasurable number of scents and scent combinations, humans and many animals can experience only five categories of taste—salty, sweet, bitter, sour, and umami (savory). In addition, the primary purpose of taste is only to tell us whether or not to eat something, whereas the purposes of scent are many and complex. Many of the subtleties of flavor that we experience as “taste” actually come from our sense of smell.
Although humans and many animals taste with their tongues, many animals taste with other body parts. Tiny animals can walk on their food, so they often can taste with their feet. Examples of these types of animals include bees and mosquitoes.
Yong says that animals have also evolved different types of taste buds depending on what they usually eat. Many animals that eat meat have taste buds that are very receptive to amino acids—the building blocks of protein—but hardly sensitive to sugars at all. Examples of these types of animals include catfish (which have taste buds all over their body) and cats. Animals such as koalas and pandas that eat lots of leaves have extra detectors for bitter tastes to warn them which plants are toxic.
Animals See Light and Color Differently Than Humans
When it comes to sight—the ability to interpret the environment based on how light interacts with it—animals differ from humans in the way they see light and color. Here, we’ll discuss each in turn.
Light
Humans have two eyes on their heads that face forward, but Yong says that’s not normal for most animals. Animals can have hundreds of eyes, which can be located anywhere on their bodies. Although almost all animals have some form of eyes, some animals see only light and dark, while others see in sharp detail at great distances. For example, a starfish has simple eyes at the tips of its arms that can sense predators, but can’t see color or detail, while an eagle can spot a rat a mile away (birds of prey are the only animals with vision sharper than humans). Yong details other ways that animals see light differently:
1) Animals with high visual acuity (sharpness), don’t have high visual sensitivity (ability to see in low or no light), and vice versa. For example, humans can see the patterns on a deer in the forest on a sunny day, but would barely be able to see the forest itself on a dark night. Mountain lions, on the other hand, can’t see stripes, spots, or other patterns on their prey, but their eyes are sensitive enough to hunt deer in low light at dusk and dawn.
2) Different types of animals have different fields of vision. Vultures, bald eagles, and other large birds of prey (raptors) frequently collide with wind turbines, even though they have excellent visual acuity. Yong explains that this is because raptors, with eyes on either side of their head, have visual fields that extend to each side of their head but not above or below it. They tilt their heads downward when they fly so their blind spots are directly ahead of them; as a result, they can’t see what’s right in front of them.
Humans often misinterpret animal behavior because we don’t understand the way they see. Yong gives the example of a viral video of a male pheasant doing a mating dance for a female, who appears to look off to the side. Viewers found the video amusing because the female seemed completely uninterested in the male’s overzealous display. In truth, the female was not looking away from the male, but was looking directly at him with her side-facing visual field.
Similarly, cows may appear to be bored or lacking in curiosity because they rarely turn their heads to look at you. But their visual fields wrap all the way around their heads, so in reality, they don’t need to turn to see you approaching from the side or even from behind.
3) Animals also see at different “speeds,” meaning some process visual cues faster than others. For example, the killer fly sees at super-fast speeds because its prey are other flies and insects, which it needs to hunt at rapid speeds.
4) In the deep sea, marine animals’ eyes have adapted to see in total darkness. The lights of a submarine can blind them or cause them to panic and even kill themselves. As a result, scientists created a camera that uses red light invisible to deep-sea creatures and lures them with blue LED lights that mimic a glowing jellyfish. This allowed scientists to study deep-sea creatures without harming them or altering their natural behavior.
Color
Color is subjective. We determine color by detecting and comparing different wavelengths of light. Objects aren’t inherently any particular color; rather, our photoreceptors (light-detecting cells), neurons (nerve cells), and brains turn light into our perception of color. Yong outlines the ways animals perceive color:
1) Animals see color to varying degrees. Many animals, such as raccoons and whales, are monochromats, meaning they can only see in shades of gray. (This is because they have only one type of color-detecting cone cell, which makes them unable to compare different wavelengths of light.) Other animals are dichromats, meaning they see two colors, along with gray. Dogs and horses, for example, see in shades of blue, yellow, and gray. Humans and other primates are trichromats. Dichromats can see only about 1% of the colors that trichromats can see. Birds, reptiles, insects, and freshwater fish are tetrachromats, meaning they can probably see hundreds of millions of colors, many times what humans can see.
Yong explains that one reason primates may have evolved to see color so vividly is to help them spot the reds, oranges, and yellows of ripe fruit (or nutritious young leaves) against a backdrop of green foliage.
2) Just as animals’ eyes evolve to see certain colors, coloration evolves depending on the eyes that are viewing them. For example, once primates evolved trichromacy and could see red, they also began evolving areas of skin that could flush with blood to convey meaning to others of their species. Yong says that even flowers evolved their colors to suit bees’ eyes, rather than the other way around. Many of the colors we see in nature result from the way animals see each other.
3) Unlike humans, most animals can see ultraviolet (UV) light. Animals use UV markings to identify all kinds of things humans can’t, such as the gender of other songbirds, the location of lichen on a UV-reflective, snow-covered hill, or an attractive male fish (some male swordtail fish have UV patterns that are appealing to females but invisible to the fish’s predators, which can’t see UV light).
Animals Can Hear Sounds That Humans Can’t
Yong writes that hearing is a unique sense because it works even when the other senses don’t: in the dark, at great distances, quickly (at the speed of sound), and through barriers. Many animals have hearing that is much more sensitive and precise than humans’, usually to help them hunt prey, avoid predators, and communicate with each other. Yong gives some examples:
1) Birds process sound very quickly. Yong says that many types of birds sing what sounds to humans like the same sequence of notes, over and over. But to the birds, these songs aren’t repetitive at all, as the birds are hearing very fast shifts in sound within each individual note that differentiate one sequence from another. Birds may use this information to do everything from creating partner bonds to dividing up parenting responsibilities.
2) Whales can hear infrasounds—very low-frequency sounds that humans can’t hear. The sound of whale songs can travel across entire oceans; one scientist used a microphone in Bermuda to listen to whale calls in Ireland. Although scientists don’t know for sure whether whales are communicating over these vast distances, some believe that whales use the echoes from their calls to map the mountains and canyons of the seafloor from great distances.
3) Many animals that appear silent to humans are actually communicating with each other using ultrasound—very high-frequency sound. In fact, most mammals can hear ultrasound, including dogs, cats, mice, and chimpanzees.
Animals Use Various Body Parts and Methods to Touch
Unlike humans, who touch primarily with their hands, animals touch using other body parts and methods, including methods that sense from afar, without the need for direct contact. Yong explains that animals can touch by sensing currents, flow, and vibrations in water, air, and soil. Here are a few ways they do this:
1) Some animals use distortions in their environment. For example, the red knot, a type of shorebird, can detect clams buried deep in the sand by using its bill to create a pressure wave of water that distorts if it hits something hard. The bird uses touch sensors on its bill to feel those distortions, allowing it to touch remotely.
Another example is harbor seals, which hunt fish using touch sensors on their whiskers that can feel the invisible wake left by fish as they swim. Fish also use sensors on their bodies to detect distortions in the water they’re displacing as they swim, allowing them to sense their surroundings in all directions so they can detect predators, prey, and their own kind (this is why they’re able to swim in schools).
2) Others use vibrations to touch. Yong says tree frog embryos can feel the vibrations of a snake chewing on their egg cases, which causes them to hatch (and, hopefully, escape!). They can distinguish these snake vibrations from other vibrations, such as those caused by rain and wind. Meanwhile, elephants can feel seismic vibrations in the ground with their feet, allowing them to sense the presence of not-yet-visible predators or other elephants.
3) Some species have specialized body parts to touch. The emerald jewel wasp kills cockroaches by stinging them in the brain, turning them into zombies that the wasps can lead by the antennae to their lair to act as a nest and food for their young. The wasp is able to do this because its stinger is sensitive to touch and can feel the roach’s brain inside its body.
All Animals Can Sense Harm, But We Don’t Know If All Animals Experience Pain
Because animals can’t tell us how they’re feeling, it’s hard to know whether various species are experiencing pain. Yong discusses what we know about animals’ nociception and pain.
Nociception
Nociception—the physical recognition of harm—takes place in the peripheral nervous system. If you’re bitten on the hand by a cat, for example, nociception occurs in your hand and your spinal cord, which tells your hand to quickly pull away from the cat’s mouth. Yong says that almost all animals, including humans, have nociceptors—neurons that pick up on harmful external and internal stimuli such as toxins, extreme temperatures, or inflammation in the body. But animals vary in the number of nociceptors they have, how easily activated they are, their size, and how quickly they transmit information.
For example, naked mole rats, which sleep in large piles in underground burrows to keep warm, have nociceptors that don’t respond to acids, meaning they don’t experience acids as harmful. This is because carbon dioxide builds up in the rats’ burrows every time they exhale, so they’ve evolved to tolerate it in much higher doses than other animals.
Pain
Pain is more than just nociception. Yong explains that pain is the conscious experience of harm, also known as suffering. Pain occurs when signals from the nociceptors travel up the spinal cord to the brain, which creates the sensation of pain. In humans, the brain is always involved in producing pain.
We don’t know whether various animals have consciousness in the same way that humans do. Consciousness stems from nervous systems, which require processing power. Not all animals have enough processing power to experience consciousness. This would seem to mean that these creatures also can’t experience pain.
On the other hand, says Yong, it’s possible that animal nervous systems work differently than human ones when it comes to processing pain. Some animals that don’t have very complex nervous systems still exhibit complex behaviors that appear to demonstrate their ability to feel pain.
For example, studies show that injecting fish in the lips with bee venom causes them to lie on the bottom of their tank, rocking from side to side, and to rub their lips against objects, long after the injections occurred. According to the scientists who conducted these studies, this shows that fish likely feel pain.
A Few Species Can Use Echolocation
Echolocation is a form of hearing in which an animal repeats sounds and listens for the echoes they return. Yong explains that this allows the animal to detect objects as well as to gather detailed information about them. Very few animals have this ability, and only bats and toothed whales (such as dolphins, orcas, and sperm whales) are experts at it.
Bats echolocate by making pulsing sounds with their mouths. They start by emitting loud, infrequent calls and make increasingly faster pulses to gather more information as they zero in on their prey.
Dolphins are so good at echolocation that they can use it to locate buried objects, distinguish between different objects based on size, shape, and material (even up to a difference of only 0.6 millimeters), and even recognize an object visually on a TV screen after using echolocation to find it—without ever having seen it.
Many Types of Fish and Some Land Animals Can Use Electrolocation
Yong writes that just as some animals use echoes to sense their surroundings, others use electricity. There are two types of electrolocation: active and passive.
In active electrolocation, creatures—usually fish—sense objects by sending out electric fields and using electroreceptors on their skin to detect distortions in those fields. Some fish that use active electrolocation are also able to engage in electrocommunication with each other, encoding information such as sex, species, and territory into their electric discharges.
Animals that use passive electrolocation can’t generate electric fields, but they can sense other animals’ electric currents and charges. All animals’ cells produce electric fields when submerged in water. Although these weak currents are generated inside the body, sharks and rays are particularly skilled at detecting them at spots where they’re exposed, such as mouths, gills, or wounds.
Yong says that electric currents need a conductive medium such as water to travel, which is why most electroreceptors are on fish or mammals that live in water. However, some land creatures can also sense electric fields. This is because, due to constant thunderstorms around the globe, the air always carries some electric voltage. Animals such as bumblebees and spiders can sense electric fields using the tiny hairs on their bodies.
Animals Such as Birds, Whales, and Sea Turtles Have Magnetoreception
Animals with magnetoreception can navigate by sensing the magnetic field created by the Earth’s liquid metal core.
Yong says that magnetoreception allows animals such as birds and moths to migrate extremely long distances without ever having done so before and even in the dark or without smell. Many other animals use magnetoreception to travel distances of every length.
Whales probably use magnetoreception to help them migrate to the same spot every year. Healthy whales that beach themselves for no apparent reason are four times more likely to do so on days with the strongest solar storms (which affect the Earth’s magnetic field). This suggests that whales are also guided by Earth’s magnetic field.
Many animals use magnetoreception to imprint the “signature” of their birthplace so they can find it many years later as adults. Some sea turtles travel hundreds of miles to lay their eggs on the beach where they were born, even though there are much closer beaches they could use. This is because nest sites need to meet very specific conditions to be successful—and the turtles know that their birthplace meets those conditions.
Part 2: Sensory Pollution Is Fatal to Animals—But We Can Change That
Yong argues that because it can be hard for humans to imagine how other animals perceive the world, we often contribute to sensory pollution, which causes significant damage to all kinds of animals. It forces animals to adapt to attacks on their senses or perish—and for many species, adaptation in a short time frame isn’t possible. Human-caused sensory pollution of animals’ environment is one of the factors contributing to a mass extinction crisis. By understanding how animals sense the world, however, we can help save animals and their environment.
Human Use of Light Causes Huge Numbers of Animal Deaths
Yong says that humans have artificially lit the night: About 83% of the world lives under light-polluted skies. Blue and white lights are particularly disruptive to animals, but they’re also the cheapest and easiest to produce.
Human-caused light pollution causes animal deaths on a grand scale, writes Yong. For example, birds die because their migrations are disrupted by bright lights or they crash into brightly lit communications towers.
Another example of the destructive effects of light pollution can be found in the behavior of sea turtle hatchlings, which die because they can no longer distinguish dark sand dunes from the brighter ocean.
Yong says that artificial light may also be contributing to the massive global decline in insects—which could seem like a good thing, but it can alter entire ecosystems. For example, an experiment in which street lights were installed in remote Swiss meadows showed that flowers in those meadows were visited by pollinating insects 62% less frequently than in non-illuminated meadows.
Noisy Human Activities Have Degraded Animal Ecosystems
Human activities such as transportation and construction have also altered our quiet places. Human activities have doubled the background noise in 63% of protected spaces (such as national parks).
Yong explains that this affects animals in many ways. Birds have difficulty finding mates because their songs aren’t loud enough to be heard over human noise. Various animals can no longer hear their prey or predators, which can cause them to lose weight and become weaker, or to abandon their normal habitat altogether. Unfortunately, there isn’t always a quieter place for them to go, as 83% of the continental US is less than a mile from a road.
The oceans have also gotten much louder, says Yong. Between World War II and 2008, global shipping has made low-frequency noise 32 times louder. This can affect marine animals in all sorts of ways; whales, for example, stop singing and crabs stop eating.
Human Activity Impacts Every Other Animal Sense
Besides vision and hearing, every other animal sense is also impacted by human activity. Yong cites a few examples: Bats crash into windows because smooth vertical surfaces, which don’t exist in nature, produce echoes that sound like open air. About 90% of seabirds eventually swallow plastic because it contains DMS. DMS is also precisely the smell that—when it occurs naturally—helps seabirds locate krill.
Humans Can Reduce Sensory Pollution to Help Save Animals and the Environment
Yong argues that understanding how animals sense the environment can help us save it. He adds that, unlike other more permanent types of pollution, such as chemical or radioactive pollution, sensory pollution can be addressed quickly and easily by simply removing the sensory stimuli that humans have added to the natural environment.
There are many simple ways to reduce sensory pollution, but economic and political incentives don’t always exist to make these changes. Examples of changes we could make to protect animals and ecosystems include sound-absorbing berms, porous pavements that absorb vehicle noise, and quieter hulls and propellers on commercial ships (already used in military ships). Even basic measures such as requiring vehicles to slow down in key wilderness or ocean areas can make a huge difference. For example, a 2007 study showed that when commercial ships slowed down by 12%, they produced half as much noise.
Other measures to address sensory pollution are more complex, says Yong. For example, when a heat wave caused a major bleaching event on the Great Barrier Reef, a marine biologist discovered that by playing the sounds of a healthy reef over a loudspeaker, he could attract baby fish back to the reef. While this isn’t a practical solution to implement on a large scale, with over half of the Great Barrier Reef gone, even small solutions help.
Yong points out that the only reason scientists could implement this solution at all is because there are still healthy reefs where they could record underwater sounds. He says that as long as such places exist, we can still save them.
