Sentient: How Animals Illuminate the Wonder of Our Human Senses

Sentient: How Animals Illuminate the Wonder of Our Human Senses by Jackie Higgins

In Sentient: How Animals Illuminate the Wonder of Our Human Senses, Jackie Higgins smoothly and successfully merges what could have been two popular science books — one on animal senses and one on human perception. Instead of separating the two subjects, here Higgins uses one as a vehicle for exploring the other.

More precisely, by examining a dozen animal species and focusing on a single sensory trait they possess, Higgins casts a clarifying light on our own sensory abilities, including those we may not even be aware of.

Each chapter focuses on a single creature and sense, as follows:

• Peacock Mantis Shrimp: color vision
• Great Gray Owl: hearing
• Star-Nosed Mole: touch
• Common Vampire Bat: pleasure/pain
• Goliath Catfish: taste
• Bloodhound: smell
• Giant Peacock of the Night: desire
• Cheetah: balance
• Trashline Orbweaver Spider: time
• Bar-Tailed Godwit (bird): direction
• Common Octopus: proprioception (sense of one’s own body)
• (An Afterword focuses on the duck-billed platypus)

The specific chapters follow an introduction that skims through a brief history of how we’ve viewed senses, noting that while most people think we have only five (taste, touch, sight, sense, smell), scientists will argue for a number more in the 20s or 30s, depending on which scientists you ask. And some, Higgins notes, will ‘argue it is folly to even try counting separate senses, as integration is about integrating information across them all, a fundamentally multisensory experience.”

The chapters themselves are concise, lucid, informative, and never fail to fascinate, even as Higgins goes well beyond simply describing the creature’s (and our) act of sensing but delves both into the mechanisms of the sense (which means getting into molecular biology, anatomy, and sometimes genetics, among other branches of science) and often how it arose, developed, and what evolutionary benefits it may be bestowed. While, as mentioned, Higgins mostly uses the animals as the vehicle for such exploration, much as Oliver Sacks once did (and Higgins in fact cites Sacks multiple times), she also brings in people who suffer from extremely rare genetic disorders or who have been the victims of traumatic injuries, using the way their senses were disrupted to illuminate the way a particular sense works. As when, for example, she tells the story of a man who lost his sense of his body and thus could not control his own limbs, though he could move them.

Two of the most interesting aspects of the book, for me at least, were Higgins’ chapters on the senses we’re less (or wholly) unaware of, and the ways in which she shows that humans, often contrary to our own beliefs, are actually pretty good at sensory perception, though we typically see ourselves as the “loser” when we compare ourselves to our animal brethren in terms of seeing or smelling.

For instance, she points to an experiment that shows that “a [human] rod photoreceptor cell can respond to a single photon and even resolve the statistics of photon numbers in weak flashes of light; that this can trigger a biochemical cascade . . . and, ultimately, this can lead to our perception of a single photon.” Granted, as the lead researcher said, “it’s more like a feeling of seeing something, rather than really seeing it … a feeling at the very threshold of your imagination — a feeling that there could have something, but you aren’t entirely sure;” but it’s still a pretty stunning result that, as Higgins puts it, “we can even detect, albeit vaguely, the individual elementary particles that make up our universe.” In similar veins, Higgins gives us experiments where humans can hear zero decibels (whispers are around 20), be trained to echolocate like bats, respond to a caress that only depresses the skin by five hundredths of a millimeter, and can track a 30-foot “twisting path marked by twine that had been dipped in the essential oil of chocolate” like a dog (in fact, humans outperform a number of animals in our sense of smell, including monkeys, otters, and rats).

As for the below-the-radar senses, these include not just the sense of body, which works more below are awareness for the obvious reason that it would be exhausting to have to pay such attention just to be able to stand (see the heartbreaking story referenced above Higgins includes regarding a man who must do just that), but also senses that were never considered part of the human realm: a sense of navigation and direction, a sense of time, and the like. These are relatively recent questions, some still being explored and debated (a raging debate over human pheromones for instance).

Sentience conveys everything clearly and concisely, in an engaging fashion, going into just the required amount of depth and detail so that the reader is left with a good understanding of the topic as opposed to being overwhelmed, and is also engaging and interesting enough that many readers will want to further explore the topic. Recommended.