American Scientist

AN IMMENSE WORLD: How Animal Senses Reveal the Hidden Realms around Us. Ed Yong. 449 pp. Random House, 2022. $30.

I would love to own a time machine, not (just) to travel back to the Cambrian Period, but also to meet the scientists of the future and the past and discuss with them what they might make of our present state of knowledge. High on my list of people to speak with would be John Lubbock, who discovered in the 1880s that ants can see ultraviolet light and that they communicate via a chemical “language.” In his 1888 book On the Senses, Instincts, and Intelligence of Animals, Lubbock wrote that “we find in animals complex organs of sense, richly supplied with nerves, but the function of which we are as yet powerless to explain.” To animals, he noted, the world “may be full of music which we cannot hear, of color which we cannot see, of sensations which we cannot conceive.”

Lubbock’s research provided the first scientific glimpses into nonhuman animal perception. A number of additional sensory capacities outside those accessible to humans are now common textbook knowledge—for instance, ultrasonic sonar in bats, sensitivity to magnetic fields in migrating birds, and infrared sensors in nocturnal snakes. If I were tasked with getting Lubbock up to speed regarding what is known about animal sensory abilities today, I’d hand him Ed Yong’s recent book, An Immense World: How Animal Senses Reveal the Hidden Realms around Us. I have no doubt that Lubbock would be thrilled beyond words by what has been discovered.

An Immense World is a hugely entertaining and insightful tour de force, a sort of Alice-in-Wonderland journey into the world as perceived by animals. It is written by a science journalist in a manner that is fully accessible to nonexperts. As a scientist who studies (and teaches about) animal sensory systems, I was impressed by Yong’s ability to explain inherently complex subjects accurately, without unduly simplifying matters. I tend to be wary of kibitzers offering their views on the “alternative realities” of animals, particularly if they speak of finding it remarkable that the world we perceive is not “reality,” as if other types of sensation indicate the existence of some metaphysical parallel universe or mean that the world we see is actually an illusion. Yong deftly steers clear of any such cheesiness.

He points out that such terms as ultrasound and ultraviolet can mislead us by making certain frequency ranges appear to be special just because they are outside the spectrum that is perceptible by humans. But humans may be unusually impoverished in some sensory areas. For instance, the vast majority of animal species can see ultraviolet (UV) light, and humans (along with a minority of other animals) are “special” only in their inability to do so. Yong calls out instances in which such terminology has led even scientists to fall victim to undue simplifications and misconceptions. A century after Lubbock discovered that ants can see shorter wavelengths than we can, such sensitivity was discovered, and subsequently fetishized, in vertebrates. For the sole reason that humans cannot see UV light, the ability of other animals to do so appeared to some scholars to enable a special “hidden” communication channel. The result was a wave of wholly unsurprising findings—such as that animals with UV color receptors use them (for instance, in choosing a mate)—and some bizarre ones: for example, the (now disproven) claim that birds of prey locate their rodent victims by looking for UV reflectance emanating from rodent urine.

Yong highlights the absurdity of this approach by imagining what a bee might say in a similar situation:

If bees were scientists, they might marvel at the color we know as red, which they cannot see and which they might call “ultrayellow.” They might assert at first that other creatures can’t see ultrayellow, and then later wonder why many do so. . . . They might wonder whether the large bipedal animals that see this color exchange secret messages through their flushed cheeks. They might eventually realize that it is just another color, special mainly in its absence from their vision.

An Immense World contains a riot of entertaining scientific findings that have stood the test of time. It is also scientifically comprehensive and up to date. The book is clearly useful not just to members of the public interested in science but to experts in zoology. It even includes a good number of findings that I was unaware of. For example, we are introduced to the thirteen-lined ground squirrel (called that because it has 13 black stripes down its back), which, because of a few mutations in a cold sensor, can survive for months at temperatures close to freezing, and when placed on a heatable plate, it won’t step off until the surface reaches 55 degrees Celsius. Of all the species that have been tested, the thirteen-lined ground squirrel and the Bactrian camel have the least-sensitive versions of a sensor that detects painful heat.

If you are a scientist stuck in the minutiae of studying a particular sensory system, it is easy to lose sight of the big picture, and to lose touch with the sense of wonder evoked by studying how the world looks from inside the cockpit of another creature. If your day-to-day grind includes (as mine does) turf wars with colleagues about such things as which particular nonlinear equation to use for converting sensory input into receptor neural signals, then Yong’s book will give you occasion to stand back and say, “Yes! This is why I am in this field, and I love it!”

Yong has met many of the field’s heroines and heroes, and he describes them as a beautiful tribe of scientists driven by the excitement and joy of discovering unexpected facets of the natural world. These scientists stand in sharp contrast to the run-of-the-mill consortium grant science that funding agencies now often seem to favor—where huge money is converted into publications with more than 100 authors but only marginal gains in terms of pushing the boundaries of science. In the field portrayed in An Immense World, many of the most important discoveries are being made by individuals who are motivated solely by curiosity, using creative methods and technology they developed themselves rather than the off-the-shelf equipment used in mainstream labs. For example, one of the scientists Yong describes, Eric Warrant, hunts nocturnal bogong moths in Australia with a contraption he calls the Eye of Sauron. Warrant has performed experiments in which he put the captured moths into an insect flight simulator surrounded by large magnetic coils and then tried to subvert their navigation in various ways. By doing this, he was able to demonstrate that bogong moths achieve their migrations of more than 1,000 kilometers by sensing Earth’s geomagnetic field, using an ability referred to as magnetoreception.

Some of the scientists Yong introduces us to are perceptually divergent, and he wonders whether experiencing the world differently from other humans is what has prompted these scholars to be curious about the diversity of animal senses. He mentions Michael Supa, a blind psychologist who demonstrated in the 1940s that he and other students who were either blind or blindfolded could detect obstacles using their hearing. The researchers exploring bat sonar at the time were aware of Supa’s work and may have been influenced by it. When the term echolocation was coined in 1944, it was applied to the skills not just of bats but of blind people.

An Immense World is organized by sensory modalities: There are chapters on smells and tastes, light, color, pain, heat, contact and flow, surface vibrations, sound, echoes, electric fields, and magnetic fields. Yong points out that the Aristotelian segregation of the senses into vision, touch, hearing, smell, and taste is both incomplete and misleading. For example, hearing, like touch, uses mechanoreceptors; also, scientists still can’t agree on what actually distinguishes the senses of smell and taste. The book has no in-text citations, but the endnotes and bibliography, which fill 68 pages, include the most important key sources.

The book ends with a melancholy lesson about sensory pollution of the environment caused by humans. When we hear the term pollution, we usually think of the kind of chemical contamination that poisons plants and animals. But humans mess with the environment in all sensory modalities. That we are losing the night through excessive use of too-bright electric light sources in our cities and beyond has been much discussed; this light pollution disrupts the diurnal rhythms of animals, their communication, their navigation, their search for mates, and their life expectancy. Sound pollution is also common. The noises from our cities and from transportation interfere with sound signaling between animals. The level of low-frequency noise from ocean shipping has increased by a factor of 32 since World War II, and Yong lists some of the results:

As ships pass in the night, humpback whales stop singing, orcas stop foraging, and right whales become stressed. Crabs stop feeding, cuttlefish change colors, damselfish are more easily caught.

The list of pollutions continues for all sensory modalities. But because these changes have taken place gradually over the past century, humans are behaving like frogs in a pot of water that is coming slowly to a boil. As sensory pollution has increased and species have gradually disappeared, we have come to accept each stage as a new normal.

Yong points out that there is still time to reverse these trends. There are many reasons to do so, including some that are in our own best interest. Noise affects human stress levels and our ability to sleep. Illuminating our settlements so brightly that they can be seen from space wastes both energy and money, and, contrary to what is sometimes alleged, there is no evidence for a link between crime and “poor” city lighting.

Many of us spend enormous sums of money to travel to distant but “serene” nature spaces. Yong builds a convincing case that we can have such environments at our fingertips, if only we take appropriate steps. Doing so will preserve the diversity of sensory worlds in the animal queendom, of which we are a part, and will enrich us in multiple ways.