What can a ballet dancer pirouetting on the spot learn from studying the fastest mammal on earth? And why did the US navy investigate the feathers of owls in its quest for stealthier submarines? These are questions that Jackie Higgins, a film-maker and author who studied zoology as a student of Richard Dawkins, addresses in Sentient, which weaves scientific research into the animal kingdom with new insights into the ways our senses function.
It was once thought that there are only five senses, but neurobiologists such as Colin Blakemore now believe there could be more than 30, each with its own dedicated receptors. Every chapter in the book tackles a different sense through an exploration of a particular animal’s specialised skill, one that has arisen from a unique anatomy, and then explores what we can learn from this about humans.We learn that the swamp-dwelling star-nosed mole has 22 tiny tentacles on its wondrous snoutIn the chapter on the circadian sense, Higgins shows how nearly all lifeforms, including humans, march to the beat of an internal timekeeper, even when deprived of the external cues of light and dark. For instance, trashline orbweaver spiders possess such an extraordinarily versatile internal body clock that scientists study them to discover whether they can help us beat jet lag. Evidence of the human body clock emerged in 1962 when the French geologist Michel Siffre cut himself off from the world in a deep cavern beneath the Alps. He stayed underground for two months in total isolation, only signalling to his supporters on the surface when he woke, ate and slept. The diary showed that he had kept a regular sleep/wake cycle despite having no means of knowing the passage of time.Higgins keeps the lay reader engaged with her lyrical and lucid style, despite describing complex science (often at the molecular level), and skilfully incorporates individual human stories. In a chapter about touch we learn that the swamp-dwelling star-nosed mole has 22 tiny tentacles on its wondrous snout. This unique feature allows it to taste its prey underwater using air bubbles and consume it at breathtaking speed. It also means that it possesses “the most sensitive touch organ of any mammal yet discovered”. The star-nosed mole’s tentacles harbour a dense network of tiny receptors, known as Merkel cells, which can detect the lightest touch and then send signals to the brain. We have Merkel cells in our fingertips. The deafblind author Helen Keller learned to communicate by lightly touching her companion’s lips and throat. Feeling their movement and vibration enabled Keller to understand the speech she could neither hear nor see.Like Oliver Sacks, to whom Higgins refers, she’s adept at describing how individuals with rare genetic disorders or life-altering injuries throw light on to our understanding of standard human senses. When the theologian John Hull lost his sight, his descent into depression was averted by his refocused hearing, which enabled him to use bat-like echo-location to navigate his darkened world.In the penultimate chapter, we learn how octopuses are the most flexible animals known on the planet, enabling them to be the Houdinis of research lab aquariums. With tens of thousands of sensory receptors all over their tentacles – their brains are only one part of their intelligence – they are masters of proprioception, the sixth sense of self-movement and body position awareness. Higgins compares their virtuosity to the fascinatingly complex story of Ian Waterman, a young Portsmouth man who was struck down by a rare neurological disease. It destroyed the nerve fibres that told his brain where his body was – he could move but could not control his limbs. But with great concentration, he trained himself to command his body by watching each individual muscle as it moved, using sight in place of his lost proprioception.As a producer of natural history documentaries, Higgins makes popular science accessible – Sentient is a dizzying display of the evolutionary ingenuity not only of lifeforms, but also of zoologists, neuroscientists and biologists who have mapped new frontiers of knowledge. You may finish reading it and wish that humans could use that intelligence to stop the destruction of the habitats all of us live in. Sentient: What Animals Reveal About Our Senses by Jackie Higgins is published by Picador (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply