Touchy Feely: How Human Senses Compare with those of other Life-Forms
Ashley Ward, Sensational: A new story of our senses | Book Review By Anna Katharina Schaffner
Science | Book Review | TLS
Did you know: the word pupil comes from the Latin pupilla, “little doll”, because we can see a tiny reflection of ourselves in other people’s eyes? A ripe tomato isn’t red, but simply reflects light with a wavelength of 650 nanometres? One in six people suffers from misophonia – a fight-or-flight reaction to unpleasant sounds – for which a hyperactive insular cortex is to blame? The earliest musical instrument is 40,000 years old, made from vulture bone and looks like a penny whistle? Half of British teenagers would rather be without their sense of smell than their mobile phones?
If you didn’t, and would like to know even more, then Sensational: A new story of our senses is the book for you.
Its author, Ashley Ward, is a professor in animal behaviour whose previous works include The Social Lives of Animals (2022). Now, in Sensational, he gives a fluent, interdisciplinary account of the development of our sensory world – one that contrasts human experiences with those of other creatures, including bacteria, crustaceans, insects and whales, and, by challenging anthropocentric perspectives, invites us to appreciate what we take for granted.
Ward dedicates a chapter each to our five primary senses before exploring a fuller “weave of perception” in the final two chapters. We may have as many as fifty-three senses. The less familiar ones include equilibrioception (the sense of balance), magnetoreception (the ability to detect the Earth’s polarity) and proprioception (our sense of our body’s position in space). There is also interoception – conscious awareness of the body’s internal workings, our heartbeat and other physiological processes.
In the chapter on hearing we learn about the association of sound with fear (exploited in horror films); that the sound of vomiting is the most hated noise on the planet; and that unpleasant sounds at specific frequencies can be weaponized against troublesome teenagers and political enemies alike. More benignly, plants can detect the gurgle of water and turn their roots towards it. The loudest sound ever experienced by humans was the eruption of Krakatoa in 1883, which may have reached 310dB. We learn, too, that complex language evolved in part because we have an extraordinarily nimble vocal tract, and because we “seem to have an inbuilt and irresistible drive to share our thoughts”.
Broadly speaking, human senses are faculties that detect stimuli by means of a specialized receptor. An example would be light entering our eye and being absorbed by the retina’s receptor cells. Via transduction, we convert these stimuli into signals that our brain can understand. Crucially, however, sensation is not perception, which involves processing and interpreting the information we receive. Our brains sift, order and filter incoming data, trying to assess what is important. Moreover, perception is far from a neutral process – it is influenced by personal biases, expectations and emotions, as well as broader cultural factors. So, while our “sensory receptors harvest a multitude of textures, pressure waves, patterns of light and concentrations of molecules to feed myriad pulses of electrical information, like an army of hyperactive stenographers, to the brain”, it is the brain that “decodes, organizes, and, ultimately, weaves meaning”. The extraction of meaning from “the jumble and chaos of physics” is, ultimately, “what makes us, us.”
In the past we were primarily interested in information about our environment: about predators and prey, competitors and mates, and whether our food and drink were nourishing or not. But our senses have evolved to tackle more complex tasks. As Ward puts it: “They are the interface between our inner selves and the outside world. They equip us to perceive beauty, from great art to the grandeur of the natural world, and to appreciate a sip of an ice-cold drink, the sound of laughter, the touch of a lover”. How our “thoughts, emotions and culture shape, and are shaped by, our sensory world” proves fascinating. Western societies typically undervalue smell, for example. Aristotle’s hierarchy of the senses has something to do with this: the philosopher put vision first, followed by hearing, smell, touch and taste. Smell is the sense that most of us are least concerned about losing. This is because, in part, “smells” were – and still are – associated with sickness and disease, with rotten food.
We understand ourselves today as visual creatures with developed auditory skills. Anglophone cultural attitudes to the senses are reflected in the English language. We say “I see” when we wish to signal that we understand something, or “sounds good” when we are in agreement. American graduates fare badly when asked to identify smells under test conditions. The Onge of the Andaman Islands, by contrast, cherish their sense of smell. They use it to navigate through the forest and, when they greet each other, ask: “How is your nose?”. Inhabitants of the Arctic are also known to rub noses by way of greeting. We ignore smell-scapes to our detriment, for smell is a powerful component in sexual attraction and can even contain information about personality type. It is also a shortcut to recollection – a phenomenon described as the “Proust effect” – because the neural pathways of the olfactory sense link “not only to the olfactory bulb, but also to the limbic system, which is intrinsic to memory formation and recall”.
The function of taste was originally to distinguish between the wholesome and the poisonous. Beyond that, what we now think delicious or disgusting is a matter for culture to decide. Ward has an unfortunate encounter with the Icelandic delicacy hákarl – fermented shark. When he samples his first “heinous morsel” he detects “a note of elderly fish, swimming valiantly against the lavatorial flow”. Icelanders would disagree. Humans taste mainly with their mouths, of course. Catfish, by contrast, are covered with so many receptors that they are “swimming tongues”. Butterflies and flies taste with their feet so that they can “register the chemical composition of things they land on”.
As for touch, it is our most social sense, whether we are “just” touching or kissing, cuddling, shaking hands and patting people on the back. Touch builds and maintains social bonds: chimpanzees and bonobos, our closest primate relatives, spend up to five hours a day stroking and de-fleaing one another. Baby rats deprived of maternal touch become nervous, chase their own tails, overeat and struggle to interact with other rats. The same is true of humans. Sadly, our society is becoming ever more touch-timid – Covid and the transference of attention to touch-sensitive screens have not helped. Yet we are still said to be “in touch with our feelings” (or not), we promise to “stay in touch”, and tricky colleagues are “touchy”. People are “thin-skinned” or “callous”; “warm” or “cold”. The importance of touch is retained by everyday speech.
Ashley Ward’s main argument is that our sensory experiences make life worth living, and that we are all sensorially unique. He reminds us that we each live in our own perceptual worlds, our own little filter bubbles. This is a good thing. We may sense things that others don’t, and vice versa, and experience and interpret phenomena in distinctive ways. This doesn’t just lend texture and nuance to our world views and social exchanges, but reminds us of the power of filters, lenses and perspectives more generally to shape our lived experience.
Anna Katharina Schaffner is Professor of Cultural History at the University of Kent. Her most recent book is The Art of Self-Improvement: Ten timeless truths, 2021