An Immense World: How Animal Senses Reveal the Hidden Realms Around Us

“This is a book not about superiority but about diversity.”

Yong again references Uexkull’s theory of the umwelt and the diversity of umwelten. There are as many umwelten as there are species. Each of these is unique to each species, and none is better than any other. Uexkull eschews traditional approaches that value complexity over simplicity, as if complexity in and of itself is of greater value than simplicity. Yong refuses human exceptionalism, or the idea that humans are different in a way that makes them superior to all other species. Instead, he and Yong ask humans to approach other animals in all their diversity.

“Nothing can sense everything, and nothing needs to. That is why Umwelten exist at all.”

Yong presents the umwelt as born out of limitations. These limitations do not carry a negative connotation but create the foundation for each umwelt. All creatures are necessarily limited in what they can sense; the limitations of sensory worlds, however, make it possible to perceive and act upon these perceptions.

“The senses of animals have fascinated people for millennia, but mysteries still abound. Many of the animals whose Umwelten are most different from ours live in habitats that are inaccessible or impenetrable—murky rivers, dark caves, open oceans, abyssal depths, and subterranean realms. Their natural behavior is hard to observe, let alone interpret. Many scientists are limited to studying creatures that can be kept in captivity, with all the strangeness that entails.”

An Immense World references a wide range of animal experiments. Some are conducted in the wild and do not harm animals in any way. Other experiments, however, involve taking animals from their homes and placing them in captivity, which causes them harm and sometimes results in death. The penetration of all animals’ homes is presented here as something to be desired and sought, and the captivity of animals is assumed to be necessary for the expansion of human knowledge. Yong raises no ethical questions here.

“I want to know what it is like for a bat to be a bat […] Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task.”

This key passage in philosopher Thomas Nagel’s “What Is It Like to Be a Bat?” insists that animals’ experiences of their worlds are subjectively unique. Bats understand the world through echolocation, a sense that humans lack, so while people might have knowledge of the sensory system of echolocation, they will never be able to understand the experience of it or, more broadly, the experience of the bat in general.

“On this journey through nature’s Umwelten, our intuitions will be our biggest liabilities, and our imaginations will be our greatest assets.”

Uexkull, in his book A Foray Into the Worlds of Humans and Animals, refers to his text as a travelogue, and Yong similarly refers to the process of learning others’ umwelten as a journey. Because intuition comes from within felt, sensory experience, Yong cautions against it. Instead, he asks people to turn to their imaginations and minds to contemplate others’ lives, understanding that they are traveling, as a kind of tourist, into foreign territory.

“Darwin was wrong, though, in calling complex eyes perfect and simpler ones imperfect. Stage-four eyes are not some Platonic ideal that evolution was striving toward. The simpler eyes that preceded them are all still around and are well suited to the needs of their owners.”

Yong, by way of Uexkull, cautions against the tendency to value complexity over simplicity, citing this anomalous analysis on the part of Darwin. There is no prototype for what eyes, in general, “should” do: Each species has a visual system that is suited to its needs. Evolutionarily, there is no ideal toward which all species are moving; each species creates its own world in which the visual system may or may not be important.

“We use the phrase ‘birds-eye view’ to mean any vista seen from on high. But a bird’s eye view is not just an elevated version of a human one.”

Yong draws attention to the ways that birds fundamentally see differently than people do and, thus, experience the world differently. Humans see what is in front of them, and, to a lesser degree, they see what is peripheral. Birds, however, generally have vision that sees all the way around them, so a birds’-eye view is not one that looks down but one that sees above, around, behind, and below. This description of birds’ visual field is incorrect due to its uncritical anthropocentrism.

“It’s possible that each of these visual speeds comes with a different sense of time’s passage.”

Yong references the critical clicker-fusion frequency (CFF), which measures how quickly the brain processes visual information. Flies process at 350 frames/second, humans at 60, and some toads at less than 1. The rate at which visual information is processed determines the perception of motion: To flies, humans probably appear to move very slowly, while to humans, flies appear to be frenetic in their motion. The higher the CFF, the slower movement appears. The sense of time—and its meaning—is relative and entirely subjective.

“Colors are not inherently magical. They become magical when and if animals derive meaning from them. Some are special to us because, having inherited the ability to see them from our trichromatic ancestors, we imbued them with social significance. Conversely, there are colors that don’t matter to us at all. There are colors that we cannot even see.”

Visual stimuli are processed so that information can be obtained, but this information additionally takes on meaning. This meaning is where “magic” occurs and moves sensory information into other realms, such as art and religion. While people can begin to understand what information other animals receive through their sensory perception, determining what meanings they create out of information may be beyond humans’ abilities.

“You might think that these pollinators evolved eyes that see flowers well, but that’s not what happened. Their style of trichromacy evolved hundreds of millions of years before the first flowers appeared, so the latter must have evolved to suit the former. Flowers evolved colors that ideally tickle insect eyes.”

Plants respond to animals’ umwelten, changing their own properties so that they might become an integral part of insects’ worlds. While the senses allow all animals to take in stimuli, the evolutionary process points to how the senses also change the development of the world, so the senses respond to the world as the world also responds to the senses, through relationships and interaction.

“Scientists who work on vision or hearing can play images and sounds at the animals they’re studying. But those who study pain have to harm the creatures they work with in the pursuit of knowledge that might improve the welfare of those same creatures.”

Yong here draws a line between humans and other animals when it comes to research. Other-than-human animals can ethically be subjected to harm and intentionally painful experiments, he suggests. Yong casts this scientific research in the realm of necessity, which makes individual animals expendable. He asks the reader to accept this uncritically.

“Given how little we know about how human brains work, let alone how those of other animals are wired, it feels premature to make definitive proclamations about whether any neurological feature is necessary for experiencing pain.”

Chapter 4 explores the difference between nociception and pain. Nociception is the detection of damage done to the body, and pain is the sensation of suffering that may follow nociception. Pain requires conscious awareness, while nociception does not. Science has historically insisted that animals do not feel pain in a way that is morally relevant. Yong calls this into question, insisting that this was presumptuous in the past and still is. Yet Yong still upholds nonconsensual infliction of pain on animals as ethical.

“Each species has its own definition of hot.”

The sensation of painful heat is tied to a heat sensor (specifically, the TRPV1 sensor). The temperature at which the sensor is activated varies by species. Extremophiles, such as camels and penguins, which thrive in temperatures that are extreme by human standards, not only tolerate these extreme temperatures but most likely also do not experience them as painful. Animals experience heat, as they experience time, differently from species to species.

“Can humans, the cause of that seismic silencing, even feel that loss?”

Humans have killed the largest mammals, causing many species to become extinct. Due to these animals’ large size and numbers, their footsteps created surface vibrations that no longer exist. These surface vibrations may have been central to many others animals’ worlds. The direct killing of some animals affects the lives of animals that are not directly killed as these effects ripple out, much as surface vibrations themselves do.

“The web, then, is not just an extension of a spider’s senses but an extension of its cognition. In a very real way, the spider thinks with its web. Tuning the silk is like tuning its own mind.”

Spiders who create orb webs can tune their webs like a musical instrument, adding tension to certain threads, making other threads thicker, and plucking individual threads to hear what is occurring on that thread. They not only tune the web; they also tune their minds via the web. Spiders think with their webs, so the web is more than a tool and is part of the spider’s mind.

“The sequences in those songs are both beautiful and useful to human ears. Birders use them to identify particular species. Neuroscientists study them because of their similarities to human languages. And yet, they might be utterly irrelevant to the birds that produce them.”

Many birds communicate through songs in which the sequence of syllables seems to be irrelevant to them. For a zebra finch, it appears that what lies within each note is important, not the sequence in which the notes appear. Humans are not able to hear or make sense of what is happening within those notes, however. The songs that people hear, then, may be entirely irrelevant to the finches themselves. The bird makes meaning in ways that people cannot understand.

“An animal’s Umwelt cannot be static, because an animal’s world isn’t static.”

House sparrows, for example, hear similarly in the fall, but in the spring the males and females hear the same tunes differently. Both sexes “retune” their hearing from season to season so that they can process relevant information, which changes from one time of year to the next. This observation may be instructive, too, in thinking about the human umwelt and the human need to “retune” in the Anthropocene.

“Like infrasound, the term ultrasound is an anthropocentric affectation.”

Infrasound is sound in frequencies lower than humans can hear, and ultrasound is sound that occurs in frequencies too high for humans to hear. People are deaf to both. Most mammals, however, hear ultrasound. Humans label sound according to their own perception of it, so the natural world is defined by human sensory systems as that which is “below” or “above” the “normal” or human range of sound waves that can be perceived. This is just one example of how language itself reflects the biased “lens” of people’s umwelt.

“Echolocation differs from the senses we have met so far, because it involves putting energy into the environment.”

Yong not only analyzes a range of umwelten. He also considers the energy that each sensory system requires in relation to other sensory systems, asking people to think critically about the benefits and liabilities of these systems.

“With ‘internal antlers,’ beaked whales could conceivably advertise to mates without needing to disrupt their sleek silhouettes.”

This example highlights potential similarities and differences among species. Appealing to humans’ sense of vision, Yong asks readers to compare the “antlers” of a beaked whale to those of a deer in the context of the beaked whale’s ability to echolocate and “see” through flesh to detect “antlers” within one another’s bodies. Yong makes this complex sensory system accessible for a reader with no background knowledge of science by presenting an image that is common in human experience and, thus, easy to visualize.

“For decades, scientists have studied electric fish in laboratories […] It is so easy to record, tweak, and play back the discharges of these animals that they have become mainstays of research in neuroscience and animal behavior […] They’ve been doing this since the 1960s, creating virtual-reality worlds for electric fish. But the animals’ actual worlds are still mysterious because they are very hard to study in the wild.”

This passage begs the question of how virtual-reality worlds can be created when the “actual worlds are still mysterious.” The electric fish studied in laboratory settings are presented similarly to the way that other animals, such as rodents, that are used as research subjects are presented in the book.

“We must study the architecture of the house itself to see how the form of an animal’s entire body defines the nature of its Umwelt. We have to look within the house to see how animals combine the sensory information from the outside world with that from inside their own bodies. And we have to gaze through every window at once, to see how animals use their senses together.”

Yong invokes Uexkull’s metaphor of a house in one of his final engagements with umwelt theory. Yong asks the reader to consider sensory systems in coordination with one another, as multiple senses, or windows, that open to the world in constantly changing and coordinating ways. The metaphor of the house once again asserts the umwelt as the most domestic of spaces, the body. Both Uexkull and Yong, who refers to domesticated and familiar dogs repeatedly in the beginning of his book, rely on the domestic to usher the reader into this journey into foreign umwelten.

“Instead of stepping into the Umwelten of other animals, we have forced them to live in ours by barraging them with stimuli of our own making.”

Yong refers to the ways that people have polluted the planet with human-produced stimuli. Rather than trying to understand other umwelten and applying that knowledge in respectful ways, humans recast the planet to suit their specific sensory desires, so the globe itself is now a reflection of humans’ umwelt. However, Yong posits that people should attempt to reduce their own output of stimuli so that the planet can support a range of umwelten.