The Revolutionary Genius of Plants by Stefano Mancuso
In one of Roald Dahl’s creepier short stories, “The Sound Machine,” an inventor rigs together a listening device that converts the inaudible screams of plants into human frequencies. When the inventor, named Klausner, plucks a daisy, he hears “a faint high-pitched cry, curiously inanimate.” Do flowers feel pain? Probably not, Klausner concludes, with typically Dahl-ian wordplay: “It felt something else which we didn’t know anything about—something called toin or spurl or plinuckment, or anything you like.”
On the surface, Dahl satirizes a vegetarian mindset: What if, like animals, our photosynthetic friends experience something like suffering and express that suffering in sound? Klausner imagines using his machine to listen to a wheat field during harvest time, where hundreds of plants would be screaming in unison, and says, “I would never eat bread after that.”
But the satire belies an even bigger, and weirder, thought experiment. Even if our linguistic ideas, like pain—itself a wildly subjective experience—do not correspond precisely to the experiences of plants, what if plants not only feel, but think, decide, and react? In a final scene, Klausner takes an ax to a giant beech tree, and the tree responds—a branch of wood high above detaches and crushes Klausner’s machine. In Dahl’s speculative landscape the plants’ cries signify not just automatic, knee-jerk noises but calculated expressions. In this world, the trees, flowers, grains, and vegetables all, in some as yet incomprehensible way, think.
In his new book, The Revolutionary Genius of Plants: A New Understanding of Plant Intelligence and Behavior, Stefano Mancuso, professor in “plant neurobiology” at the University of Florence, argues, in short, that Dahl’s world may not be fantasy, but reality. According to Mancuso, not only should we appreciate plants more—both for the necessity of plants to human existence (food, fuel, shelter, etc.) and for their sheer beauty (in nature, in gardens, as architectural models, etc.)—but also because “plants exhibit unmistakable attributes of intelligence.” In the first two-thirds of the book, Mancuso describes, chapter by chapter, plants’ “intelligent” acts: memory retention, deliberate movement, mimetic behavior (copying other plants), manipulation of other organisms, and structural reactions to the environment.
Some of Manusco’s analysis of vegetative actions are, quite simply, startling. In the chapter on mimesis, a vine in the forests of Chile can, like an Iguana, mimic its environment. But this magical Boquila is not limited to color, like its lizard analogue; the plant is a three-dimensional chameleon: mimicking in a “near-simultaneous” transformation the “shape, size, and color” of the “most diverse” types of leaves. How does this super-vine know what shape, size, and color to take? Most likely, Mancuso argues, the vines possess a “visual capacity.” The Boquila perceives the leaves around it and mimics their shapes. Without eyes, the plants see.
In another chapter, Mancuso explains experiments on the plant Mimosa pudica—also covered excellently in the “Smarty Plants” episode of the podcast Radiolab. The Mimosa is notable because the plant quickly closes its leaves when disturbed. Nineteenth-century scientists were fascinated by the Mimosa’s movements and, after experimentation, showed that its leaves could acclimate to certain disturbances. One researcher, Monica Gagliano, retested this historical thesis: dropping the plant, repeatedly, in short falls of four inches. After a number of falls the plant got used to the disturbance and stopped curling itself up. The Mimosa “knew” the falls were not dangerous. But the researchers wanted to find out if the plants “retained the memory.” Forty days later, Gagliano dropped the acclimated Mimosa and the plants still did not close their leaves: They “remembered” the drops were not dangerous.
Okay, so plants exhibit behavior that looks like they “mimic” and “remember,” but if these rooted creatures really do analyze these images and store memories, where and how do those thoughts occur? Plants have no brains! In fact, plants have no organs at all. While animals are mobile and centralize processes in organs—the lungs breathe, the kidney filters the blood, the brain thinks—plants are immobile and so cannot centralize, literally by design—a tree must be able to let some of its leaves be eaten without dying. As Mancuso puts it, “any function that in animals is concentrated … is spread throughout the entire body of plants.”
The answer to the question of brainless intelligence may be found by investigating this fundamental difference between the carbon-consuming and carbon-producing kingdoms—where animals concentrate thought in that one heady organ, plants spread their computational process throughout. In perhaps his most intriguing chapter, “Green Democracies,” Mancuso compares plant intra- and inter-organism networks to the ancient Athenian assembly, bee hives, and Wikipedia. Consider the decision faced by a new hive about where to settle. Bees that have found good spots perform an excited dance. The largest and most enthusiastic group of dancing bees wins its choice of location. Such a system of collective, consensus-based decision-making resembles other networked groups, like democracies, the internet, and even the brain itself. “The neurons in our brain,” Mancuso writes, “which produce thoughts and sensations, work the same way as the bees.” This is key: If plants do think, they do so not with one organ, but with collective and distributed networks of cells and roots.
The final third of Mancuso’s book deals less with plant observations and more with human inventions, largely Mancuso’s own projects, that mirror plant structures: a “Jellyfish Barge” (JB) greenhouse that uses only seawater to grow lettuce, and Martian robot probes designed to act like small plants. Sometimes, plants’ design Mancuso relies on seems less molded by plants’ specific intelligence but by evolution’s; for instance, unlike the shape-changing Boquila, the cactus doesn’t mold itself—that happened over millions of years of natural selection.
Besides this logical objection, the final chapters also fell short stylistically. Mancuso thinks up undeniably cool inventions, and it’s no wonder he was able to secure funding, yet in writing about his own genius, Mancuso often lapses into self-conscious braggadocio: “‘Either projects win prizes or they go on the market.’ And it looks as though JB … is destined only to win awards.” Let’s return to the plants’ genius, please.
Like this final section, the digressive anecdotes occasionally sound a little too proud of themselves. For example, Mancuso calls Lamarck “the father of biology—in the literal sense of the word, having coined the term himself,” and he reflects on a rarefied privilege of experiencing zero gravity by noting, “you never forget your first parabola.”
In general, however, and despite the occasional bragging, I appreciated the cultural and first-person contexts. Mancuso’s chosen historical details were as often as not eclectic gems: quotes by Charles Darwin’s poet grandfather, carriage ride experiments in Paris, or a long section on lily-pad-esque structure of London’s Crystal Palace of 1851. The personal details were just as earnest instead of pretentious, such as a memoir-like scene where Mancuso describes falling in love with the taste of chili peppers at a long, hot August wedding in Southern Italy.
Similarly, though Mancuso can stumble in his prose, with cliched overstatements like, “our advances in research on this issue have potential beyond our imagining,” most of his language flows in that difficult lane between scientific specificity and not too much jargon. These skillfully navigated sentences allow his central analytical ideas, like those seed burrs, to stick to you and cling for days. The book’s stunningly illustrated with two-page spreads of root patterns that also lingered in my mind as visual representations of the brain-like nature of plant structures. What if a sentient forest isn’t just the fantasy of Tolkien’s ents, The Wizard of Oz’s fighting trees, or countless other fantasies of conscious woods, but a reality where roots think?
Perhaps Manusco’s greatest stretch of metaphorical language, and likewise what may be the book’s most provoking idea, comes right after the chapter on democratically thinking bees. Mancuso considers the capacity of plants for “manipulation” and, as he says, “I use this word deliberately.” Consider, Mancuso offers the Acacia tree, which not only feeds ants nectar in return for the colony’s services as guards—the ants keep away predators and clear the area of competitor plants—but the tree also feeds ants chemicals that work on the ant’s nervous system, such as caffeine, nicotine, and more. The Acacia literally hooks its servant ants with drugs. In this, what Mancuso calls a “vile story of manipulation and deception,” the plant times its servings just right: first offering the ants “sweet nectar rich in alkaloids, and then, once the ants are addicted … control[ling] their behavior” using those drugs.
Then, with a narrative sleight of hand, Mancuso shifts to chili peppers, lapsing emotional on his love for this ubiquitous fruit. But, Mancuso suggests, maybe chilis do not serve those millions of human spice enthusiasts by providing its tasty jolt; instead the chili is manipulating us. The chili is the Acacia, we humans are the ants.
And why would a plant spend extra energy producing a chemical that seems to affect no other animal but humans? Simply, “to secure the most powerful and versatile mammalian carrier,” or in other words, to spread itself via humans all over the world. This is a masterful rhetorical role reversal: Plants no longer seem “at the mercy of animal needs” but are themselves masters of human needs. We don’t cultivate plants, plants cultivate us. (I write this while drinking a large cup of coffee; are those innocuous beans manipulating me?) The thought is as humbling as it is jarring: Not only are the roots below and the leaves above thinking about us, they are also thinking about how to use us.
In Dahl’s world, Klausner’s sound machine picks up superhuman frequencies of plant life; their sounds really aren’t meant for us. But in Mancuso’s telling, we humans are the intended recipients for plants’ signals—it’s as if the chili peppers were sending us a letter marked with that powerful capisum chemical. It’s not that we can’t hear their language without help; it’s that we receive the chili’s signals, we respond, and we are manipulated, all without knowing, really, what or why the plants are saying.
A shorter version of this review appeared in the print edition of DigBoston.