Review: 'Planta Sapiens' by Paco Calvo

Is a plant capable of experiencing surprise?

To assess this question, consider what happens when you experience surprise. Typically you encounter a discrepancy between what you expect to happen and what actually happens: Perhaps you awaken expecting to see sun streaming in through your windows based on the previous night's weather forecast of clear skies and a warm day. Instead, the sky is gray and snow is falling.

But in what sort of situation might a plant experience surprise? In "Planta Sapiens: The New Science of Plant Intelligence,"Paco Calvo, writing with Natalie Lawrence, emphasizes that we must ask questions of this nature if we are ever to understand plants’ awareness and their subjective experiences of the world. Calvo asserts that plants do take in the "mismatch between expectation and experience" that amounts to surprise.

Calvo is a philosopher and the principal investigator at the Minimal Intelligence Lab (MINT Lab) at the University of Murcia in Spain. He attributes to plants cognitive as well as emotional capacities. In his view, it is entirely misguided to insist that a brain is necessary for an organism to think. Calvo knows this is a "radical" perspective, one that "challenges the foundation of the human experience." It's time that we overcome the "plant blindness" that afflicts our "zoocentric" or animal-focused view of the world.

Plants express their cognitive capacity in many ways. It is seen, for example, in the way many plants avoid high concentrations of salt in the soil because salt stresses their roots and inhibits protein synthesis. When a plant's root tips spread into previously unexplored soil, "they keep note of the salt gradients they encounter, moving toward decreasing levels of salt that might lead the way to new patches of habitable soil," Calvo writes. In his view, plant roots making an adjustment in these circumstances is an expression of surprise. If salt concentration tapers off, the roots respond positively and continue along their way. If the roots only encounter more salt, however, "the state of surprise remains high" and they seek alternative routes.

Plants do move — and not just via their roots or in exceptional cases like the famous Venus fly trap snapping shut. Charles Darwin knew as much back in the 19th century. "All plant organs move: from root tips and tendrils to leaves and flowers," Calvo explains. "They all sway in circles as they grow, a pattern which Darwin called ‘circumnutation.’"

Without question, plants do respond in complex ways to changes in the environment. Plants often orient toward the sun. Is this response merely adaptive — a kind of reaction genetically encoded into the organism — or instead cognitive, a more flexible, learning-based action, one that might even be anticipatory instead of reactive? The Cornish mallow plant turns its leaves toward the sun "before the sun is even up," Calvo writes. He deems that a predictive act. "The leaves don't turn in response to the sun, they are ready in anticipation of sunrise."

How could a plant predict anything in the absence of a brain? Plant cells lack the nerve cells found in animals, but we should look instead to the plant's vascular system, along which electrical signals travel. There lies a reasonable analogue to the nervous system of animals.

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But let's look more closely at the Cornish mallow's movement toward the sun. This plant uses starch granules to track the sun's position. Here's how it works: Sunlight causes the mallow to build up sugars that convert to starch; in the morning, the starch accumulates on the side of the stem where sunlight hits. When darkness arrives, the plant converts that starch to energy. Owing to the greater amounts of starch on the side of the plant the sun hits at sunrise, more granules remain in that location through the night, which causes water in those particular cells to be regulated differently. This asymmetry in turn causes a directional bending: The stem now leans "toward sunrise even before the sun has come up." Skeptics will find an adaptive explanation more satisfying here than one rooted in plant thinking.

To his credit, Calvo — while freely admitting he was not trained as a plant scientist — cites articles by plant experts critical of his perspective. At the same time, though, he conveys a sense that naysayers are just not sufficiently open-minded to accept plant experience for what it is. Along with other scientists, I have spent much of my working life documenting thinking and feeling behaviors in animals that for decades weren't thought to be possible; any outright dismissal of Calvo's views on my part would amount to an unfortunate irony. Scientists do need to think out of the box, and to entertain innovative ways of looking at plants. (In this regard, Calvo might have discussed Robin Wall Kimmerer's "Braiding Sweetgrass: Indigenous Wisdom, Scientific Knowledge and the Teachings of Plants.")

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Yet too often, Calvo undermines his own case by using over-the-top language (he references plant dignity, for example) and inappropriate analogies to human behavior. Most egregious is his comparison between misunderstood plants and patients with "locked-in syndrome," people who "exist outwardly in a vegetal state but who have an awareness of what is going on." Here he borders on the offensive; to state what should be obvious, extremely disabled people do not in any way resemble plants.

Despite the book's drawbacks, Calvo raises some fascinating questions. Might we more successfully cope with the climate crisis if we see plants as active agents in the environment, not only as resources for carbon capture? If plants suffer as well as think — Calvo suggests they do in part because they respond to anesthesia — should there be a movement for plant rights, as there is for animal rights?

Calvo recounts a meal he ate on a KLM flight, in which much was made by the airline of the ethics of the bread, cheese, eggs and meat served. To be sure, animal rights activists would contest those ethics, but Calvo asks a different question: "Have KLM thought of the garnish, the carrots, peas and potatoes that go with the chicken breast? If the main thesis of this book is correct, plants … have subjective experiences of the world. So shouldn't we care about plants for their own sake?"

Are we meant to take seriously the rights of carrots, peas and potatoes? How would the world's billions feed themselves without eating plants? Those questions, Calvo does not tackle.

Barbara J. King, professor emerita at William & Mary, is the author of several books on anthropology and animals, including "How Animals Grieve." Her latest book is "Animals’ Best Friends: Putting Compassion to Work for Animals in Captivity and in the Wild."

The New Science of Plant Intelligence

By Paco Calvo with Natalie Lawrence

Norton. 285 pp. $28.95

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