BookBrowse Reviews Sentient by Jackie Higgins

BookBrowse:

With enthralling examples from across the natural world, filmmaker Jackie Higgins artfully explores the science of the senses in her debut book Sentient.

Swooping noiselessly on its five-foot wingspan, the great gray owl can hear a mouse rustling under a mound of snow from 100 feet above. The Goliath catfish, studded with hundreds of thousands of taste receptors all over its body, can taste trace amounts of amino acids shed by other fish swimming at a distance in the murky waters of the Amazon River. The tiny star-nosed mole, though nearly blind, can identify and capture prey in as little as 120 milliseconds with the exquisitely fine-tuned touch sensors on its distinctively shaped snout, while the amorous male giant peacock moth can smell a mate from miles away.

In comparison with these stunning feats of perception, our own sensory powers may seem ordinary and dull. As Jackie Higgins argues in Sentient, however, studying the perceptual prowess of our relatives across the animal kingdom can help us to better understand how our own senses function—illuminating, as the book's subtitle suggests, just how remarkable our sensory abilities are. "Our furred, finned, and feathered relatives offer insights across the range of human experience," as Higgins puts it. "Through their eyes, ears, skins, tongues, and noses, our familiar and ordinary become unfamiliar and extraordinary, and curious new senses emerge."

Though our olfactory powers don't quite rival those of the bloodhound, the average human nose can still smell at least a trillion different scents. In fact, our sense of smell surpasses even that of several other species thought of as "super-smellers," including mice, rats and shrews. We are capable of detecting hundreds of thousands of audible tones, perceiving millions of shades of color and seeing in light conditions a billion times dimmer than daylight—not too unlike the deep sea-dwelling spookfish, whose reflective eyes allow it to detect the slightest light rays in the gloom of the ocean abyss.

Over the course of the book, Higgins introduces readers to a menagerie of creatures—from peacock mantis shrimps and octopuses to orbweaver spiders, cheetahs and duck-billed platypuses—to illustrate the ingenuous sensory mechanisms our animal kin have evolved in adaptation to the world around them. In each case, these examples serve as a springboard for discussing parallels in the sphere of human perception, showing that our senses are both more powerful and more varied than we may commonly assume. Indeed, beyond touch, taste, vision, smell and hearing—the classic notion of five senses inherited from Aristotle more than 2,000 years ago—scientists now think we may have upwards of 22 senses and counting, including a sense of time, sense of direction and sense of proprioception, or the ability to create an internal map of the body's position and movements.

Focusing on a dozen such senses—including some disputed ones, such as the ability to sense pheromones, or hormone-like chemicals secreted by the body—Higgins blends research from biology, psychology and neuroscience to shed light on the specialized sense receptors that work together to generate our complex perceptual awareness of our environment.

Discussions of continuities across the natural world highlight the common evolutionary heritage we share with every other sentient creature—"there is more to unite us than divide us," as Higgins says. And fascinating case studies of unusual neurological conditions help to elucidate the underpinnings of human perception by identifying the experiences of those who are outliers. For example, there's the Australian artist whose rare mutation gives her enhanced color vision and the South Pacific islanders who can only see shades of gray; the young boy immune to pain and the psychology professor so hypersensitive that the feel of fabric is agony; the butcher's assistant who loses his ability to perceive his own body and the patient plagued by "taste phantoms"—mysterious experiences of nonexistent tastes.

A graduate of Oxford University with a master's in zoology, Higgins has a talent for explaining complex scientific concepts in an accessible way, and her graceful prose and captivating examples make Sentient a delight to read. Engaging, thoughtful and evocative, the book is a marvelous paean to the "everyday miracle of being sentient," as Higgins puts it. At the same time, it is also a humbling reminder of our own limitedness.

Wondrous as our senses are, they put us in touch with mere slivers of experience, allowing us to grasp but a tiny fraction of our surrounding environment. We perceive a mere ten-trillionth of the electromagnetic spectrum. We lack the vampire bat's thermal perception and the bar-tailed godwit's astounding ability to sense direction through minute shifts in the earth's magnetic field. We cannot even imagine what it would be like to sense the world through electricity, like the duck-billed platypus.

Like every other sentient being, the reality we experience is filtered through and constrained by the perceptual tools we have evolved to use. "We can only experience what we first sense," as Higgins writes. Thus every animal, with its own distinctive set of sensory powers, offers a different perspective on the planet we share, a different lesson on how to make sense of the world.

Reflecting on the dazzling range of animal abilities Higgins discusses, it's hard not to think of the vast number of species facing extinction because of climate change and habitat loss and to wonder what diverse and miraculous ways of being sentient may disappear before we've even discovered them.

This review was originally published in The BookBrowse Review in March 2022, and has been updated for the November 2022 edition. Click here to go to this issue.