PDF Summary:An Immense World, by Ed Yong

A cow can see you coming without turning its head, even if you’re behind it. Seabirds create mental “maps” of the ocean using their sense of smell. Sharks use electrolocation to sense weak electric fields emanating from inside their prey—especially from openings like mouths, gills, or wounds.

In his best-selling book An Immense World, science journalist Ed Yong describes the many unique ways that animals perceive their environments, demonstrating that the world is far richer and more nuanced than humans’ five senses are capable of perceiving. Understanding animals’ sensory lives isn’t just fascinating—Yong argues that it can also help save animals from extinction.

In our guide, we’ll examine, sense by sense, how animals experience 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. Along the way, we’ll provide history, research, and data to contextualize Yong’s ideas.

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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.

How Research Into Animal Hearing Can Help Improve Human Hearing

Studying animals’ ears and the mechanics of how they hear has helped scientists develop treatments for human hearing loss and improve hearing aid technology.

For example, studies conducted on a species of fly with specialized ears have led to technology such as mini-microphones in hearing aids that can sense the direction a sound is coming from (the fly they’re modeled after has the best directional hearing in the animal kingdom). Studies of rats, which have an auditory system similar to that of humans, have helped scientists better understand noise-induced hearing loss in humans. In addition, studies of owls and lizards have helped scientists gain more insight into common hearing loss in humans. Many of these studies involve measurements and observations of the animals’ superior hearing ability, rather than experimentation that harms the animals.

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.

The Social Purpose of Touch

In addition to using various forms of touch to detect prey and predators, animals—including humans—use physical touch as a means of deepening social bonds and promoting emotional and physical health.

Research demonstrates that primates like rhesus monkeys and chimpanzees groom each other not only for hygiene purposes, but also to decrease stress and aggression (female chimpanzees break up fights between males by grooming first one, then the other) and to garner social favors (a chimp is more likely to share food with another chimp that’s previously groomed it).

In humans, studies show that romantic partners are more likely to report higher levels of relationship trust and satisfaction the more they engage in “grooming” behaviors, such as wiping away the other’s tears or running their hands through the other’s hair.

In addition, both animal and human babies require physical touch for development and even survival. Studies of rats and monkeys demonstrate that babies taken from their mothers experience anxiety, depression, and, in the case of rats, a weakened immune system. Research also shows that premature human babies, who have an increased risk of death in their first few weeks, are 51% less likely to die if they’re given “kangaroo care,” which consists of a parent repeatedly holding their baby against their bare chest for extended periods.

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. (Shortform note: Scientists believe that understanding more about how nociception works biologically in animals, especially in simpler invertebrates, could lead to better ways of treating pain.)

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.

The Ethics of Animals’ Pain

Examining whether and to what degree various animals feel pain can help humans understand the ethical implications of killing animals for food.

In his famous 2004 essay, Consider the Lobster, author David Foster Wallace (known primarily for the novel Infinite Jest) examines the ethics of boiling lobsters alive during food preparation. While Wallace doesn’t reach any definitive conclusions, he considers it significant that lobsters exhibit behavior consistent with pain, scrambling desperately to escape upon being placed into pots of boiling water. He notes that even if lobsters experience only a primitive form of suffering, humans may be obligated to prevent such suffering; the same argument could apply to all animals we eat.

Indeed, many people believe that we shouldn’t eat meat because it causes animals unnecessary suffering. They argue that industrial livestock farming ignores animal welfare and inflicts pain upon sentient beings.

For example, cows are transported to slaughterhouses in crowded, poorly ventilated trucks where they can suffer from heat stroke; once they arrive, they await slaughter in pens where they can often hear, see, and smell other animals being killed. Yet studies show that cows experience fear and anxiety; they also perceive the stress of other cows and become more fearful as a result. In other words, cows feel anxious and fearful prior to slaughter. During slaughter, cows are hit with a stun gun, then hung upside down to bleed to death. If they are improperly stunned the first time, they may experience severe pain as they are repeatedly hit with the metal bar of the stun gun—or they may bleed to death while still conscious.

Despite Wallace’s unease, a simple crustacean might not have a nervous system complex enough to experience pain; its behavior might simply be a product of nociception. On the other end of the spectrum, cows are highly intelligent and have similar nervous systems to humans, meaning they’re capable of processing pain in a similar way.

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.

(Shortform note: Studies show that echolocation is an even more sophisticated ability than scientists previously thought. For example, a 2024 study demonstrated that in addition to using echolocation to perform short-range tasks like locating prey and avoiding obstacles, bats can use echolocation to create longer-range mental maps that allow them to navigate over several kilometers. In addition, research attempting to create visual images of what dolphins “see” using echolocation suggests that dolphins can create a 3-D “picture” of a human diver so detailed that they can even make out the diver’s weight belt—all using only sound.)

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 like 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, like mouths, gills, or wounds.

(Shortform note: Animals’ ability to use natural electricity predates humans’ ability to generate electricity by millions of years. In fact, the invention of the first battery was inspired by the South American electric eel, a large creature from the Amazon River capable of generating so much electricity (600 volts) that it could cause serious harm to a horse. Italian physicist Alessandro Volta observed the organs of electric eels and came up with the idea of stacking different metals together to generate electricity. Before his invention of the synthetic battery in 1800, the only way for people to generate electricity was by rubbing two materials together to create static electricity.)

Yong says that electric currents need a conductive medium like 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 like bumblebees and spiders can sense electric fields using the tiny hairs on their bodies.

(Shortform note: Bees’ ability to sense electric fields may mean that they can predict the weather. One study found that bees spent more time foraging for food outside of the hive on the days before rainy days than they did before dry days. This could be because they sensed atmospheric changes that occur prior to rain or thunderstorms.)

Animals Like 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 like 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.

(Shortform note: A 2023 study demonstrated that magnetoreception is likely more common in animals than once thought. Scientists discovered that a molecule present in all living cells can make animals sensitive to magnetic fields—if there’s enough of it. Their research suggests that many animals in addition to those we already know about have magnetoreception. Earlier research into animal behavior found that even dogs seem to have magnetoreception, which they can use instead of or in addition to smell for navigation. They employ odd methods of doing this: Many dogs align themselves along a north-south axis when defecating, which scientists believe may help them map their location relative to other spots, such as their starting point.)

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.

(Shortform note: As outlined in journalist Elizabeth Kolbert’s book The Sixth Extinction, scientists believe we’re in the midst of a sixth mass extinction event. Unlike previous, prehistoric extinctions, the sixth extinction is the result of human activity, including human-caused climate change and ocean acidification, habitat destruction, and the spread of invasive species around the world. In the 50 years from 1970 to 2020 alone, the average size of world wildlife populations has shrunk by 73%, including a 95% decline in Latin America and the Caribbean.)

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.

(Shortform note: Blue and white LED lights first became available in the 1990s, and due to their lower cost, higher energy efficiency, and brighter lighting abilities, they quickly began to replace sodium lamps (which produce a yellow light) in many European streetlights. However, studies show that LED streetlights have significantly increased blue light pollution in Europe. This has resulted in negative changes in animal behavior as well as negative effects on humans’ circadian rhythms and sleep. Researchers say these problems can be mitigated by better lighting design, such as by using LEDs that are less blue-rich and ensuring outdoor lighting is targeted and low-level.)

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. (Shortform note: The number of birds in North America alone has decreased by 30% since 1970, due primarily to habitat loss and climate change, as well as to sensory pollution. Birds are necessary to our economy and food supply because they eat insects that destroy crops, they play a key role in pollination, and they disperse seeds to create new forests.)

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. (Shortform note: Of the seven species of sea turtles, three are endangered. Sea turtles are critical to maintaining a healthy ocean and fisheries, in part because they maintain the sea grass that provides a habitat to various species of fish.)

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.

(Shortform note: Research shows that in the last four decades, there has been about a 45% decline in insect populations. Yet insects are the base of the entire food chain, feeding birds, reptiles, and small mammals, which in turn provide food for larger animals. Insects are also crucial to agriculture: They pollinate more than 75% of crops, at a value of up to $577 billion a year. They also act as the world’s cleaning crew by decomposing waste and organic matter. For example, dung beetles are worth about $380 million a year to the US cattle industry because they break down manure and churn rangeland soil.)

Noisy Human Activities Have Degraded Animal Ecosystems

Human activities like transportation and construction have also altered our quiet places. Human activities have doubled the background noise in 63% of protected spaces (like 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.

(Shortform note: Other effects of noise pollution on animal behavior include difficulty navigating, reproducing, finding food, and communicating. Noise pollution can cause animals stress, fear, pain, and hearing damage; studies show that long-term exposure to loud noise reduces memory and learning ability in some animals. These effects, in turn, impact animals’ survival, contributing to the decrease in wildlife populations across species.)

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.

How Ocean Noise Pollution Endangers Marine Life

The effects of human-caused ocean noise on marine animals’ behavior—and survival—are even more extensive than Yong describes.

In addition to global shipping, ocean noise is caused by ship sonar and seismic air gun blasts used in oil and gas exploration. Air guns fire every 10 seconds day and night for months at a time, producing the loudest noise of all, at up to 260 underwater decibels. Container ships reach up to 190 underwater decibels. These sounds equal about 200 and 130 decibels in the atmosphere, respectively; by comparison, the launch of a space shuttle is about 160 decibels. And sound travels underwater much faster and farther than in the air.

Scientists say these noises can kill marine life gradually or even instantly in the case of zooplankton like krill, which form the basis of the whale’s diet. Human-caused ocean noises also decrease marine animals’ reproduction, alter migration, impair hearing, cause brain hemorrhaging, and mask communication sounds necessary for survival. Ocean noise pollution has a particularly severe impact on whales and dolphins, who use echolocation to hunt, navigate, find mates, and communicate with one another.

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. As we’ve discussed earlier, DMS is also precisely the smell that—when it occurs naturally—helps seabirds locate krill.

(Shortform note: Researchers have identified three ways in which sensory pollution impacts species fitness (defined as their mortality and ability to reproduce): misleading, distraction, and masking. Bats’ and seabirds’ responses to sensory pollution are examples of misleading, which happens when an animal reacts to a sensory pollutant as if it’s a natural signal. Distraction occurs when an animal’s attention is taken away from what it’s doing, as when traffic sounds distract an animal from hunting. Masking is when sensory pollution overwhelms the stimuli in the natural environment, as when whales can’t hear each other’s songs due to all the ocean noise generated by human activity.)

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 like 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.

(Shortform note: Because sensory pollution is only one of many factors affecting the recent drastic decline in biodiversity, animal species’ survival can also benefit greatly from any efforts to address other factors. For example, warming air and ocean temperatures caused by climate change can shrink or destroy animal habitats; however, we can slow climate change by curbing fossil fuel emissions. In How the World Really Works, scientist Vaclav Smil argues that, while the world is heavily reliant on fossil fuels, there are still many actions governments and individuals can take to reduce emissions, including better home insulation, land and forest conservation, transitioning to electric vehicles, cutting down on food waste, generating electricity from renewable sources, and using nuclear energy.)

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.

Why Should We Save Animals and Their Habitats?

Throughout An Immense World, Yong focuses on the intrinsic value of animals and the ethical argument that, because human activities cause animals harm, we have a moral imperative to save animals from harm. As he suggests, however, not everyone sees the intrinsic value of a frog or a bee. Some argue that protecting animals and their habitats may have negative economic consequences, such as limitations on land development and resource extraction, increased transportation and industrial costs, or job loss.

Aside from suggesting some economically viable solutions to sensory pollution, Yong doesn’t address these arguments. But a large body of scientific research indicates that wildlife conservation and preserving biodiversity doesn’t just benefit animals, it also benefits humans: —data indicates that biodiversity is essential to our food security, our health, and our economy:

1. Food security. Each species plays a unique role in its ecosystem, contributing to the overall health and stability of its environment. The loss of a single species can disrupt ecological balance, leading to negative cascading effects on other species and ecosystem functions. Pollinators like bees are a primary example of this: Their extinction would drastically affect plant reproduction, which, in turn, would severely reduce our food supplies.

2. Health. Biodiversity helps protect against disease. Research shows that 60% of infectious diseases come from animals. With human activities expanding into animal habitats, animals are forced to live closer to each other and to humans, leading to the spread of zoonotic diseases. Conversely, protecting natural ecosystems leads to lower instances of diseases such as Lyme disease and malaria.

3. Economy. Research shows that more than half of the world’s Gross Domestic Product (GDP) is dependent on nature. Businesses that rely directly on animals and their habitats run the gamut from wildlife tourism to commercial fishing. Natural ecosystems also provide jobs for billions of people globally.