Imagine you are a Pulitzer Prize–winning science journalist for your reporting on the pandemic for The Atlantic. What do you do in your downtime? How about cranking out a New York Times bestseller? An Immense World is a multisensory exploration of the many ways in which animals perceive their environment. Some of these senses are familiar to us, others are utterly alien, all of them reveal that the world humans perceive through their senses is only a slice of a much larger world.

An Immense World: How Animal Senses Reveal the Hidden Realms Around Us, written by Ed Yong, published in Europe by The Bodley Head (a Vintage imprint) in June 2022 (hardback, 480 pages)

From the OMG-factor of insects with ears on their knees to animals with more sensitive hearing than us, when writing about animal senses, it is easy to emphasize the weird or the superlative. Ed Yong is not interested in comparisons or lists but in trying to understand animals on their terms. One touchstone is of course Thomas Nagel’s famous 1974 essay but the lodestar of this book is a concept defined in 1909 by the Estonian-German zoologist Jakob von Uexküll: that of an animal’s “Umwelt” (literally translated its “environment”). Whereas the previously reviewed Sentient introduced this concept belatedly in its epilogue, Yong sensibly opens with it and offers a crisp definition: every animal “is enclosed within its own unique sensory bubble, perceiving but a tiny sliver of an immense world” (p. 5). This book is a sensory smorgasbord spiced up with some particularly fine writing in which Yong discusses the work of scientists past and present, and mixes literature research with interviews.

Smell, the detection of molecules in your environment, is a skill so useful and basic that even single-celled organisms do it. But it is also hard to study: we cannot predict smell from molecular structure, and it is hard to capture and play back smell in an experimental setup. Vision is easier, but eyes come in a bewildering variety. Jumping spiders dedicate one pair to sharp vision and another pair to motion detection. Scallops have hundreds of eyes lining their shell, but absent much of a brain they might very well see without experiencing vision. Other Umwelten include ultraviolet light, polarized light, and colours we cannot comprehend. Hummingbirds can distinguish between colours that look the same to us, thanks to an extra, fourth type of photoreceptor (they are tetrachromats, we are trichromats). And mantis shrimp? Despite at least twelve types of photoreceptor, their vision is organised completely differently and turns out to be rather poor. But what haunted me was Yong’s description of the Umwelt of the squid that dwell in the deep and have obscenely large eyes. The sperm whales that hunt squid do not glow, but they do trigger bioluminescent flashes as they collide with plankton. The squid, it seems, “scan one of the darkest environments on Earth for the faint sparkling outlines of charging whales” (p. 82).

“This book is a sensory smorgasbord spiced up with some particularly fine writing in which Yong discusses the work of scientists past and present, and mixes literature research with interviews.”

The chapters on mechanoreception were particularly delightful. The star-nosed mole uses its tentacled nose as a touch organ: “with every press, its environment comes into focus in a starburst of textures […] like a pointillist image appearing dot by dot” (p. 162). Animals can sense flows of air or water (e.g. the hydrodynamic wake left by fish), such that: “touch extends into the recent past […] whiskers can feel what was, rather than simply what is” (p. 175). Treehoppers—this blew my mind—produce vibrations that travel through plants, inhabiting a world that can be made audible with contact microphones. Even sound is more multifaceted than just the infra- and ultrasonic calls beyond our hearing. Some birds completely retune their ears seasonally depending on what information matters most, e.g. trading off pitch sensitivity during the mating season with temporal resolution for the busy chatter when migrating in large flocks. Yong nicely builds towards Umwelten that are increasingly hard for us to understand. I have a renewed respect for bats after reading his list of ten challenges of echolocation. Meanwhile, some fish can both produce and sense electric fields to find prey, detect obstacles, and communicate—and might not even distinguish between these activities. And magnetoreception has us flummoxed despite decades of research as we still have not identified a clear organ for it. Yong is suitably cautious here, highlighting the many mistaken claims, the competitive research field, and the risk of experimental error when working on something we cannot sense.

The chapter on pain, in particular, exemplifies the maturity and nuance that Yong brings to his exploration of sensory biology. You might think that, as a progressively-minded person, he is going to convince you that, of course, animals feel pain. Well, it is complicated. For one, it is an emotive and controversial topic and Yong spots an artificial dichotomy: animals are frequently either assumed to experience pain exactly as we do or not experience it at all. It is conceptually challenging for us to imagine what an intermediate state might be like, but there is no reason to assume it feels the same across the entire animal kingdom. Though pain is a useful mechanism warning of danger and injury, animals “differ in what they must avoid and what they must tolerate” (p. 120). For instance, male praying mantises continue mating while being eaten by the female. To us, this sounds excruciating. Does this show that insects prioritize one thing, e.g. reproduction, over another? Do they tolerate it? Or do they simply not feel it because they cannot alleviate it? Yong introduces the distinction between nociception (the sensory process of detecting damage) and pain (the suffering that ensues); a distinction some people object to. After all, for other senses “we rarely distinguish between the raw act of sensing and the subjective experiences that ensue“. However, Yong argues, that is not “because such distinctions don’t exist. It’s because they usually don’t matter” (p. 124). Pain is unique in being the unwanted sense, the one we try to avoid, he adds. Finally, what hinders a better understanding is the instrumental attitude that hides behind these debates. “When we ask if animals feel pain, we’re asking less about the animals themselves, and more about what we can do to them. That attitude limits our understanding of what animals actually sense” (p. 133).

“The chapter on pain, in particular, exemplifies the maturity and nuance that Yong brings to his exploration of sensory biology.”

Though the chapter on pain stands out for being particularly thoughtful, the whole book is suffused with instances where Yong quietly disabuses the reader of pseudoscientific ideas, superstitions, or paranormal explanations. The collection of footnotes is amongst the most interesting you will find anywhere. Studying animal senses is hard and asks for humility. Why? Because we do not understand the stimuli that we do not experience, and risk misunderstanding the ones we do, interpreting them through our own senses. Because most sensory biologists spend their careers studying a single sense while animals rely on multiple senses simultaneously. Because sensory experiences could very well blend. Octopuses, for example, have arms lined with both taste and touch receptors. Does that mean they touch and taste at the same time or is it a single, fused experience? And because our experiences appear to us as “purely mental constructs divorced from physical reality“. In myths and stories, we imagine transferring our consciousness into the body of another animal to experience their world. Instead, “an animal’s sensory world is the result of solid tissues that detect real stimuli and produce cascades of electrical signals. It is not separate from the body, but of it. You can’t simply imagine how a human mind would work in a bat’s body or an octopus’s, because it wouldn’t work” (p. 333). I found it to be one of the most profound messages of this book. On the back of all of the above, the last chapter, where Yong discusses sensory pollution, hits extra hard. During the time that we learned more about animal senses, human activities have increasingly flooded animal Umwelten with stimuli, with light and noise pollution being the best documented.

The only recent book that comes close to what Yong has done here is Martin Stevens’s Secret Worlds, which is a somewhat briefer affair, though Stevens brings his expertise as a sensory biologist (he also authored the textbook Sensory Ecology, Behaviour, & Evolution). Yong, however, brings his exquisite writing and skill at capturing scientific nuance for which his reporting is famous. Strictly speaking, it would not be correct to say this book is out of this world, as it is so fully steeped in it. Let me just say An Immense World is a sensory revelation that had me so utterly captivated that I did not want it to end.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

An Immense World

Other recommended books mentioned in this review:

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Animals are frequently celebrated for their exceptional senses, being able to hear, see, or smell things that we cannot. In Sentient, zoologist and television documentary director Jackie Higgins shows that some of this research has taught us more about how humans perceive the world, while other research reveals that we are less of a pushover in the sensory department than we previously thought. And do we really have only five senses? We need to talk about Aristotle.

Sentient: What Animals Reveal About Our Senses, written by Jackie Higgins, published in Europe by Picador in June 2021 (hardback, 344 pages)

I admit that I initially misjudged Sentient, thinking it was going to be another book about the wonderful world of animals senses à la Martin Stevens’s Secret Worlds. There are plenty of fascinating critters in this book but the clue is in the subtitle—Sentient is as much about human senses and their neurological and psychological underpinnings. This research, as Higgins points out at the start, is upending the classic notion of “the five senses” of touch, taste, vision, smell, and hearing that Aristotle posited. We have many more sensory receptors, with the total anywhere from twenty-two to thirty-three, depending on who you ask. Sentient is a smart survey of twelve such senses with each chapter juxtaposing research on animals with that on humans.

Several chapters deal with the classic five senses and introduce exceptional animals. The eyes of the mantis shrimp contain some twenty different types of photoreceptors, perceiving not just colour but also properties such as polarization. According to neurobiologist Justin Marshall, “400 million years ago, one of them got hold of an optics text book and now they are a physics lesson on a stick” (p. 12). The nose of the star-nosed mole looks like a hand and provides a sense of touch, but acts more like an eye, having taken over the visual cortex in the mole’s brain. And catfish have a skin that is covered in taste receptors, to the point that they “do not possess a tongue, as we know it. Their whole body is their tongue” (p. 127).

“Classic research by Adolf Butenandt showed pheromone communication in moths […] Despite tantalising research in humans […] we have yet to close the circle Butenandt-style and identify the substances involved.”

Other senses are more contested. Classic research by Adolf Butenandt showed pheromone communication in moths. By identifying and then synthesizing the chemicals in question, it “created the model for how we should go about pheromone analysis” (p. 183), according to zoologist Tristram Wyatt. Despite tantalising research in humans by way of lap dances, smelly t-shirts, female menstrual cycles^[1], and speed-dating on (androgen) steroids, we have yet to close the circle Butenandt-style and identify the substances involved. Some have thus rejected the notion of human pheromones. Wyatt takes a more moderate position: “pheromones have been identified in almost every animal you can think of […] if the entire kingdom is awash with airborne aphrodisiacs, why should we be any different?” (p. 184). Animal navigation and sense of direction is a huge topic on which much has been written. Higgins limits herself to bird migration and details the two rival theories for how birds perceive Earth’s magnetic field. Might it be by crystals of the iron mineral magnetite found in the body, or rather by light-sensitive proteins in the eye dubbed cryptochromes?

Finally, several fascinating chapters deal with less obvious senses. Cheetahs are known for their speed, but it is their sense of balance that steals the show. Their vestibular organs in the inner ear are exceptionally well developed compared to other cats. Walking on two legs the way humans do is similarly “one of the most daring balancing acts in the animal kingdom” (p. 203), and we have similarly enlarged balance organs for a primate. Pioneering studies in which people retreated to caves, shut away from daylight, revealed an inner sense of time and established the field of chronobiology. A third type of photoreceptor diffusely present in mammalian retinas, neither rod nor cone, has been implicated in this. Finally, mechanosensory neurons give us a sense of body awareness or proprioception, telling us where our body is in space. A patient who suffered from a rare form of body-blindness has shown parallels with the octopus whose arms are only partially controlled by the central nervous system.

“Next to animal research, Higgins shows how we have learned much about human senses from those unfortunate souls who were afflicted by neurological disorders or suffered accidents.”

Next to animal research, Higgins shows how we have learned much about human senses from those unfortunate souls who were afflicted by neurological disorders or suffered accidents. Drawing on the work of the late Oliver Sacks and others, she describes cases of blind people who visualise their environment through sound or touch, those whose colour vision is enhanced or completely absent, those whose pain receptors make them either immune or hypersensitive to pain, those who have no sense of smell or suffer from olfactory hallucinations, and so on. Time and again, neuroplasticity plays into this, with brain regions normally dedicated to one sensory modality rapidly being usurped by another when one sense goes missing. And this is not unique to humans. Regarding vision, one researcher quoted here puts it like this: “It’s provocative, but we’re arguing that the brain may not be organized into sensory modalities at all […] The striate cortex is visual only if you have vision” (p. 94). It does answer that old chestnut of whether a tree falling in the forest makes a sound if there is nobody to hear it. On one level, yes, pressure waves are being produced; but on another level, no, perception happens in the brain.

One recurring theme is that, when put to the test, humans perform surprisingly well. Higgins describes experiments in which subjects perceived single photons, heard sounds down to zero decibels, or smelled substances at concentrations normally reserved for dogs. This might leave you with the impression that humans are, perhaps, supersensers after all. The epilogue puts this into perspective by introducing, arguably rather late, Jakob von Uexkülls’s concept of the umwelt, “the slice of the surrounding environment sensed by an organism“. David Eagleman writes that “Our brains are tuned to detect a shockingly small fraction of the surrounding reality” (p. 288), something that is further explored in Ed Yong’s book .

Sentient stands out for explicitly building a bridge between the fields of animal sensory biology and human neurology and psychology. My impression is that one usually plays second fiddle to the other in many other books. Higgins, however, balances her coverage well and includes incredibly interesting studies from both fields, making this book appealing to readers interested in either field.

1. ↑ Supposedly, women living together would synchronise their menstrual cycles. Higgins takes this to be true, only paying lip service to the enduring controversy: “the results have been met with scepticism and many scientists […] are still in need of persuasion” (p. 182). My impression is that this was subsequently shown to be an artefact. A good write-up of the arguments pro and contra can be found on the Modern Fertility blog.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Sentient

Other recommended books mentioned in this review:

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“Dinner with Darwin: Food, Drink, and Evolution”, written by Jonathan Silvertown, published by The University of Chicago Press in November 2017 (hardback, 232 pages)

Silvertown starts off recapping Wrangham’s thesis put forth in Catching Fire: How Cooking Made Us Human, shortly mentioning the role of fossil teeth that Ungar elaborated upon in Evolution’s Bite: A Story of Teeth, Diet, and Human Origins. He then traces our migration around the globe following the heaps of empty shells we left around the world’s coastlines. Domestication secured our food supply, and the reader is given a summary of the beginning of agriculture in what is now the Middle East, something that was covered more in-depth in my recent review of Against the Grain: A Deep History of the Earliest States. We are also introduced to the seed collection efforts of Russian scientist Nikolai Ivanovich Vavilov (more on him in Where Our Food Comes From: Retracing Nikolay Vavilov’s Quest to End Famine and my review of Never Out Of Season: How Having the Food We Want When We Want it Threatens Our Food Supply and Our Future). Silvertown delves into the biochemistry of taste and the budding discipline of neurogastronomy, while a side-dish of fish allows him to discuss the importance of smell on our experience of flavours.

Meat and livestock are an entry point to discuss the genetic changes involved in domestication (in passing touching on Dmitry Belyaev’s work that was reviewed in How to Tame a Fox (and Build a Dog): Visionary Scientists and a Siberian Tale of Jump-Started Evolution). A chapter on vegetables sees Silvertown delving into the biochemistry of plant chemical defences, which we circumvent through cooking and food processing. Spices and herbs, on the other hand, are valued for their chemical compounds, as discussed in a second chapter. The chapter on desserts finally made me understand that not all sugars are created equal, revealing how fructose hoodwinks our metabolism, hormones, and digestion, and has become a prime suspect in obesity and diabetes. Microbes and fermentation (on which more in my review of The Rise of Yeast: How the Sugar Fungus Shaped Civilisation) play a role in the production of cheese, beer, and wine. We even get a crash course on the evolution of altruism when discussing the sharing of food.

” […] “A heroin addict is a bystander casualty of the war between poppies and caterpillars” (p. 154)”

Finally, Silvertown discusses the future of food. He summarises the first green revolution and role of Norman Borlaug (more on him in The Wizard and the Prophet: Two Remarkable Scientists and Their Conflicting Visions of the Future of our Planet) and stresses the importance of genetic engineering of crops in launching the second green revolution, which we will need to meet the challenges of a changing climate and expanding population. He makes short work of the non-sensical arguments put forth by the anti-GMO movement (something on which I have written much more in my review of Seeds of Science: Why We Got It So Wrong On GMOs). If anything, genetic engineering is as natural as it gets – nature has been doing it for a very long time, as shown by the discovery of horizontal gene transfer (the transfer of genetic material between species done by bacteria and viruses, see my review of Quammen’s book The Tangled Tree: A Radical New History of Life). Even the tools that we use, including the most recent discovery of CRISPR-Cas9 (see my review of A Crack in Creation: The New Power to Control Evolution for more details on that), have been taken straight from nature’s (cook)book.

It’s amazing that Silvertown manages to cram all this, and much more, in in under 200 pages. This book is a veritable feast for the popular science buff and food lover. The finger-licking selection of chapters provides a good entry point to various topics, summarising a lot of recent primary literature. Silvertown is a gifted writer who engages as much as he amuses. His observation (p. 154) that “A heroin addict is a bystander casualty of the war between poppies and caterpillars” is the kind of wit you would expect from a biologist. Before I opened this book, I wasn’t sure whether I would enjoy it much (I’m really not sure why anymore), but it turns out this book sits right in the middle of subjects I have been reading about a lot lately. This entertaining read would also make the perfect gift for your foodie friend.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Dinner with Darwin paperback, hardback or ebook

Other recommended books mentioned in this review:

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