48 pages 1 hour read

Ed Yong

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

Nonfiction | Book | Adult | Published in 2022

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Summary and Study Guide


An Immense World: How Animal Senses Reveal the Hidden Realms Around Us (2022) is written by Ed Yong, a British American science journalist who won a Pulitzer Prize in explanatory journalism for his coverage of the COVID-19 pandemic. In addition to An Immense World, Yong is also the author of I Contain Multitudes (2016), which explores the relation between animals and microbes. An Immense World won the Carnegie Medal for Excellence in Nonfiction and was a finalist for the National Book Critics Circle Award in Nonfiction. This study guide refers to the 2022 hardcover edition of the book.

Content Warning: The source material refers to a wide range of animal experiments in the sciences, many of which involve the nonconsensual captivity of animals, often causing them harm and sometimes death.


An Immense World attempts to approach animals’ sensory perceptions through the bio-philosopher Jakob von Uexkull’s 1909 theory of the umwelt (plural, umwelten). The umwelt refers to the species-specific sensory worlds in which animals live and out of which they make sense of the outside world. Yong asserts that he is interested in learning about animals in and of themselves to help people understand their lives, as opposed to trying to learn more about human lives through theirs.

This journey through the sensory lives of animals (Uexkull referred to his work on umwelten as a travelogue) is grounded in a biological overview of a wide range of species’ sensory systems and how these systems turn stimuli into information that each animal can then act on. The theory of the umwelt insists that each species makes sense of the world uniquely and in a way specific to its needs. Uexkull’s theory is radically egalitarian: No umwelt is superior to another.

Uexkull’s theory of the umwelt guides Yong’s philosophical approach to animals’ lives as valuable in themselves, but his work is also informed by biology and the seemingly basic, but complicated, question of how many senses there are. Aristotle’s classical definition of the senses includes only five: vision, hearing, smell, taste, and touch. However, there are many more senses than these, and Yong organizes the book around the following stimuli: smells and tastes, light, color, pain, heat, contact and flow, surface vibrations, sound, echoes, electric fields, and magnetic fields. Yong examines these stimuli to explore what animals do with them. He claims that an introductory understanding of the ways that various species process stimuli will open human imaginations to a broader appreciation of their umwelten and their lives.

Along the way, Yong draws the reader’s attention to the difficulties of this attempted understanding. Humans exist in their own umwelt, one from which they cannot remove themselves. For example, humans rely primarily on their sense of vision, and this informs the language that is available to describe the sensory perception and experiences of other species, even when these species do not process the world through vision. Humans’ sensory world cannot help but cloud their vision—note the visual metaphor used here—of their sensory worlds. Even when people share the same senses with other animals, the information gained from these senses may be entirely different for animals than for humans.

Yong insists that people must attempt to imagine the sensory lives of other species, despite these and other limitations. Though the umwelt of each species is different, common ground lies in the fact that all animals are sentient, meaning that every animal attempts to make sense of what lies outside its body. This requires all animals to neurologically differentiate between themselves and what exists outside them.

Yong concludes An Immense World with an investigation of sensory pollution. Humans have manipulated the world to conform to their own umwelt without considering the umwelten of others. For example, because humans can see sharply due to having high-resolution vision but cannot see in the dark because they do not have light-sensitive vision, the planet is covered with artificial light. This allows people to see whenever they please. However, many animals depend on the darkness to navigate, and this artificial light is blinding to them. Yong focuses on light and noise pollution, which he distinguishes from chemical pollution and other forms of pollution that cannot be immediately solved, as they are caused by toxins that will remain present for thousands, if not millions, of years. Sensory pollution, however, can be immediately addressed and cleared from the environment, enabling animals to participate fully in their own umwelten. Yong insists that people have a responsibility to address this pollution.

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