Summary
Ed Yong’s An Immense World explores the vast diversity of animal sensory experiences, urging readers to transcend human-centric views of perception. Drawing from the concept of Umwelt - the unique perceptual world of each species - Yong illuminates how animals interpret their environments through their senses - some completely foreign to humans, like ultraviolet vision, echolocation, or magnetic field detection. The book emphasizes that no creature, including humans, experiences reality in its entirety. Instead, animals have evolved sensory systems tailored to their needs, creating a mosaic of perspectives on the world. The narrative delves into these sensory wonders, with chapters organized mostly according to particular senses. The book ends by advocating for preserving the integrity of natural sensory environments threatened by human activity.
There were several interesting themes that I really appreciated in the book. My favorite theme was that there are typically intrinsic trade-offs to certain senses. For example, the sensitivity of vision is directly opposed to the acuity of vision. Another fascinating theme is that sensory organs are used in very different ways by different creatures - such as using "hearing" to create spatial maps like "vision" in humans, or even combining touch and electrosensation in the bill of a platypus. Finally, an important theme that kept coming up was how humans impose our own Umwelt when we try to understand other animals, such as thinking that the beautiful tails of Luna moths are to attract mates because they are so visually stunning - when in reality, they seem to be tools to jam the sonar of bats.
The first chapter introduces the concept of Umwelt, a term coined by Jakob von Uexküll to describe an organism’s sensory world.
The second chapter takes on smells and tastes, which are the oldest senses that exist in virtually all living creatures. The chapter focuses on animals for which smell dominates, such as dogs, ants, and elephants. Ant behavior is so completely orchestrated by smell, that an ant will pick up and treat a living worker as dead if it is treated with the right pheromone, despite it moving around and protesting. In those experiments, I kept wondering how the living ant that smelled dead perceived itself.
The third chapter discusses light and the huge variety in the way that different animals use light. And chapter 4 builds on the light chapter to talk about color vision. I thought it was interesting that the number of color-sensitive opsins found in animal didn't necessarily go into its color vision. And in fact, it seems unlike that any animals are more than tetrachromats.
The next chapter covers pain and spends time differentiating between nociception and emotional suffering. There's an interesting discussion on some animals reduced sensitivity to stimuli that is painful to humans because of physiological adaptations (like high CO2, or extreme heat and cold).
Chapter 5 builds on the discussion of temperature sensors and discusses heat detection. Insects detect thermal radiation to help them dodge and move through environments, since they heat up so quickly. And certain snakes use infrared sensitivity to "see" heat signatures of their prey.
Chapter 6 discusses touch and flow perceptions. This chapter was cool because a lot of animals have very fine touch discrimination, but use it for different purposes and the sensors are found on different parts of their bodies, such as sea lions tracking the movement of fish through water currents sensed by whiskers.
The next chapter focuses on a special touch sense that senses surface vibrations, from spiders and insects to elephants.
Chapters 8 and 9 focus on the sense of sound, from infrasonic rumbles to ultrasound, which evolves into a more in depth discussion of echolocation, and how sound can be used to make spatial maps.
Chapters and 10 and 11 focus on the sensation of electric and magnetic fields. Electrosensation can be both passive or active, where the animal sends out electric pulses. The mechanism of sensing magnetic fields is still not all the way known and super difficult to study because a magnetosensor doesn't necessarily have to be exposed.
Chapter 12 focuses on multisensory integration and brings up the important point for animal sensory experiments that in the natural world, animals rarely use just one sense to complete a particular objective.
The final chapter is a call to action to reduce sensory pollution because of how devastating it can be to other animals.
I thought the book was a grand tour of the sensory worlds of animals, and I learned a lot. I also had some previous knowledge, that I had learned earlier in life, corrected by more recent experiments. This is a great book if you're looking to experience some awe and wonder at the many solutions nature has found for creatures of all kinds to thrive in their niches.
Discussion Questions
- This book was chock full of sensory facts about other animals. Which sensory facts were your favorites?
- Did reading the book change how you perceive your own sensory experiences or your relationship with nature? What kinds of senses have you been paying more attention to?
- I loved the theme presented throughout the book about certain intrinsic sensory trade-offs. For example, hearing can specialize in temporal resolution or frequency resolution and vision can specialize in sensitivity or acuity. I remember in graduate school mentioning to my advisor that it would be really cool to see infrared light, and he responded by saying that if that happened to him, he would really miss water being transparent, which blew my mind. What other trade-offs do you think humans have baked into their senses?
- In a way, hearing about other animals’ awesome senses, but also their limitations, made me feel even more empowered and happy with human senses. At least for me, when I hear about other animals’ sensory feats, I often sort of attribute all of my sensory ability onto the animal PLUS this additional awesome thing it can do. But often it is lacking in abilities that seem trivial to me. Were you particularly surprised by any of the limitations of other animals that stuck out to you?
- In graduate school, a scientist funded by the Department of Defense gave a presentation to us about his research on mimic octopuses because he was investigating this question to develop better camouflaging technology. When you were reading the book, did you think of any other translational applications of the sensory feats of animals?
- Do you think that humans have an obligation to balance human progress with the sensory well-being of other species?
- Throughout the book, Yong highlights our tendency to interpret the world through our own human Umwelt. I was thinking about how we "leave no trace" in wilderness based mainly on our dominant sense of vision - and that this act of leaving no trace is really meant for other humans even though we often make it sound like it is for other animals. But very few animals would likely be as perturbed by wrappers and litter as they probably are perturbed by our lingering smells and products. How else do you think our human sensory bias affects how we interact with, conserve, or exploit other species.
- In the discussion on pain, Yong distinguishes between nociception, which is the presence of specialized nerve cells that detect damaging stimuli and pain, which is an emotional experience that requires higher-order processing. Then he makes a case for animals likely experiencing pain based on a few lines of evidence. There are similar pain systems in humans and at least other mammals. Animals show behaviors consistent with pain avoidance and management (such as rubbing themselves after an irritant is put on their skin), and sometimes make complex decisions that weigh a reward against the pain endured to find that reward. Were you convinced by this?
I found it interesting that Yong uses a programmed robot as an obvious example of something that does not consciously feel pain. But I could also imagine very easily programming a robot to do all of these behaviors. My viewpoint is that there is good reason to act as if other animals experience pain, but that we don't have nearly enough knowledge about how subjective experience works to be able to predict which animals have it, no matter how complex their behavior. On the other side, Yong points out that for many creatures, especially non-social ones, that not adapting behavior in the face of pain would often be more advantageous for survival or reproduction.
- As a scientist, I was impressed by Yong's discussion about how animals usually use multiple senses to solve any of its real world problems, which makes senses difficult to study when relying on animal behavior. In general, it's easy to attribute behavior in the presence of a "lesion" to a function, but it's important to remember that behavior in the presence of a "lesion" shouldn't be overinterpreted. What do you think would be the best way to conduct sensory experiments in animals when relying on behavior?