Planta Sapiens review by Paco Calvo – aliens in the garden | science and nature books

IIn Denis Villeneuve’s 2016 film Arrival, the US military asks a linguistics expert to decipher the complex language of the seven-limbed aliens (“heptapods”) who landed on Earth. It is a memorable and indeed moving attempt to portray the immense challenges involved in bridging the chasm of mutual misunderstanding between two completely different species.

I thought of Arrival while reading the remarkable book by Paco Calvo, the fruit of “two decades of passionate exploration of a rich and alternative world that coexists with our own”: the world of plants. The subject of his exploration is surprisingly radical: the question of whether plants can be said to possess intelligence.

Calvo is Professor of Philosophy of Science at the Minimal Intelligence Laboratory at the University of Murcia, Spain. Although he presents detailed scientific evidence to support his case, he also relies on philosophical arguments about the nature of consciousness. We humans tend to believe that the world revolves around us, but Calvo writes that intelligence is “not as special as we like to think”. He argues that it is time to accept that other organisms, however radically different, may be capable of this.

“I have a lot of fun with my tendrils”, Darwin wrote to a friend in 1863. Confined to his sickbed for weeks, the author of On the Origin of Species busied himself studying the movements of the cucumber plants on his windowsill. During his convalescence he was forced to live slowly – “to become more vegetal”, writes Calvo – and this stillness opened his mind to the wonder of his vegetal companions: “It allowed him to see them more in their own way, to experience plant life at the pace of plants.

Darwin was clearly a guiding presence in Calvo’s attempt to open a new scientific frontier: “He learned to think differently and clearly outside the frameworks in which most of his contemporaries happily confined themselves.” The result of his confinement with cucumbers was a 118-page monograph on The Movements and Habits of Climbing Plants. Darwin realized before anyone else that these movements were in fact “behaviours”, comparable to those of animals. And observing behavior is the path to understanding intelligence. In plants, it reveals a range of faculties “ranging from learning and memory to competitive behaviors, sensitive to risk, and even numerical capacities”.

Over the course of his book, Calvo describes numerous experiments that reveal the remarkable range of plants, including how they communicate with others nearby using “chemical conversation,” a language encoded in approximately 1,700 volatile organic compounds. It also shows how, like animals, they can be anesthetized. During lectures, he places a Venus flytrap under a bell jar with a cotton ball soaked in anesthetic. After an hour the plant no longer responds to touch by closing its traps. The tests show that the electrical activity of the plant has stopped. He is indeed asleep, just like a cat would be. He also notes that the seed germination process can be halted under anesthesia. If plants can be asleep, does that imply that they also have a waking state? Calvo thinks so, as he argues that plants are not just “photosynthetic machines” and that it is quite possible that they have an individual experience of the world: “They can be aware.”

Other studies show that certain plants remember where the sun will rise, in order to turn their leaves towards the first rays. They store this knowledge – an internal model of what the sun will do – for several days, even when kept in complete darkness. The conclusion must be that they are constantly collecting information, processing it and retaining it in order to “predict, learn and even plan ahead”.

Of course, these are revolutionary ideas and, as Calvo admits, contested by many scientists who study plant physiology. But he patiently guides us through the latest research and builds a compelling case that, however unlikely it may seem, is worth taking seriously.

It is clear that plants do not have brains in the colloquial sense of the term. But although they lack our gray matter, Calvo thinks they have a unique “green matter.” In the absence of nerves, plants use networked cells to regulate themselves. Their vascular system is made up of tubes arranged in layers, like the cortex of mammals, which run from the root to the shoot. It transmits electrical signals, like a “green cable that carries information throughout the plant”. It is here, he suggests, that we must look for a “phytonervous” system. Calvo admits, however, that it is too early to say whether, in even the most complex plants, it is “the functional equivalent of a hierarchical but diffuse brain”.

Venus flytraps can be anesthetized, just like animals. Photography: Cynthia Shirk/Getty Images/iStockphoto

Basically, Calvo’s important book is about changing our perception of plants. He points out that without them “human life would be untenable”. Faced with the reality of the climate crisis, we must accept plants as “co-inhabitants of the planet”. Understanding this reality could lead to a fundamental shift in our view of our own role in the biosphere and help us work to rebalance our destructive effects on it. As in the film Arrival, embracing the otherness of a fundamentally different form of life could transform both our understanding of ourselves and our role on the planet.

Calvo has a wonderfully infectious enthusiasm for his subject that makes this book, for all its complex science, a pleasure to read. It challenges us to step out of our “zoocentric” perspective and radically change our view of plants: from robot-like mechanisms to complex organisms with varied behaviors, responding to and anticipating their environment. In doing so, he wrote a truly inspiring book.

Planta Sapiens: Unmasking Plant Intelligence by Paco Calvo with Natalie Lawrence is published by Little, Brown (£14.99) on August 25. To support the Guardian and Observer, order your copy at Delivery charges may apply.