By Katie L. Burke, award-winning editor and science reporter. He is a senior contributing editor at American Scientist. Originally published in Undark.
In 1973, the best-selling book “The Secret of Plant Life” was published, raising questions about plant emotions and communication. Even if you haven’t read this book, you’ve probably heard of self-explanatory tests: playing classical music and rock and roll to plants, for example, or hooking yourself up for a polygraph. The book even inspired a movie with a song by Stevie Wonder.
The experiment was a fun idea, but poorly designed. Scientists strongly reject this book and distance themselves from its ideas. “According to the botanists working at the time, the damage caused by Secret Life in the field cannot be overstated,” writes Zoë Schlanger in her new book “The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth.” .” “In the years that followed,” says Schlanger, “the National Science Foundation became reluctant to give grants to anyone who was testing the responses of plants to their environment.” And, he continues, “Scientists who were pioneers in the field changed course or left science altogether.”
It took almost 40 years – a generation of scientists – for that chilling effect to mount. In the last 15 years, funding for plant behavior research has returned, at least in small amounts. Schlanger serves as a tour guide to this history and the pressing questions posed by new research about the shared future of plants and humans.
Considering the history of research on plant intelligence, the subtitle of this book may raise doubts. Even popular books like “The Hidden Life of Trees” have been criticized for getting ahead of the evidence when it comes to plant communication. But “The Light Eaters” reveals that: Schlanger’s thinking is strong and he explains these intellectual debates against each other with a sense of fairness and curiosity.
There is a clear excitement in Schlanger’s efforts to meet the few scientists who have been able to push the field forward. His explorations take him around the world: in the Chilean rainforest to see a plant that mimics others like a chameleon; the Hawaiian island of Kaua’i, which has an incredible number of rare and endangered plants; and the University of Bonn in Germany, meeting with one of the founders of the Society for Plant Neurobiology (now called the Society of Plant Signaling and Behavior). It was not easy for the scientists he met along the way. Although a few of the lucky and brave have carefully designed a niche, Schlanger meets many who put their careers on the line of researching the extraordinary abilities of plants to feel their world; others sadly left the field altogether. Others put their research on hold for decades, turning to teaching or more lucrative research questions.
Despite the challenges in this field, Schlanger finds inspiration in his story, which is very different from his work as a weather reporter, where he starts to burn because of all the painful stories he deals with every day. “Journalists in my line of work tend to focus on death. Or your harbingers: disease, disaster, decline,” he wrote. He wanted to be close to life, to celebrate it, in a way he rarely did in his day job. He writes: “In this time of destruction on earth, plants provide a window to a green way of thinking. Earth’s plants “fill our atmosphere with the oxygen we breathe, and they literally build our bodies with the sugar they get from sunlight,” he continued. “They have their own complex, dynamic lives – social lives, sex lives, and a whole host of subtle appreciations that we think are only the domain of animals.”
“Understanding plants will open up a new area of understanding for humans: that we share our planet and owe our lives to a form of life that is subtle in itself, at once unknown and familiar.”
Indeed, Schlanger includes how plants sense and react to their environment – or evidence that they have such senses, even if scientists don’t know the underlying mechanisms. Plants communicate not only through chemicals in the air and soil, but also, possibly, through sound. Air bubbles expand as water travels from the plant’s roots up its stems, emitting an ultrasonic click. Each type of plant tested – wheat, corn, grapes, and cactus, for example – has a different density. Plants can sense touch and transmit electrical signals, too, which provides another means by which they can communicate. And these creatures sense light in complex ways that make it comparable to vision; a vine that grows in the Chilean rainforest, Boquila trifoliolata, can mimic nearby plants down to leaf shape, texture, and venation pattern, although no one yet knows how to “see” its neighbors. Plants also have memory and social behavior. A plant of the nettle family, Nasa poissoniana, can anticipate when a pollinator will visit its star-shaped flowers, based on the periods of time between visits, and will raise its pollen-laden shadow.
Yet plants do not have brains: Their intelligence is not centralized, but rather a distributed network. “How is information about the world integrated, evaluated for value, and translated into action that benefits the plant?” Shlanger asked. That’s the main question in the research, and whether plants can do it is an ongoing — and heated — debate. Schlanger appears to be partial to the idea put forward by neuroscientist Giulio Tononi that the complexity and integration of electromagnetic wave patterns reflects the level of human consciousness. Consciousness, in this view, is a spectrum, not a binary.
One of the pitfalls of accessing language to describe these phenomena is that it is almost impossible to avoid a certain degree of anthropomorphization. Explaining how botanists have viewed the use of the word intelligence, Schlanger writes: “Evaluating plants by human perception was absurd; it just made the plants like little people, little animals.” However, plants “use several senses – or one might say, intelligence? – far surpasses anything humans can do in the same category.” Scientists have wrapped this information in “layers of fences, a language that distances plants from us in any way,” ultimately making it challenging for their work to reach the public or other fields. Schlanger argues that humans need understandable metaphors. – which they can connect to but misrepresent how plants are different from humans. Or, he thinks, we need to “plant our language,” calling the traits “plant memory,” “plant language,” or “plant sense.”
The cabbage caterpillar feeds on the leaf of the Arabidopsis mustard plant, stimulating a calcium wave in the plant that triggers a defense response in other leaves. Calcium is visible by fluorescent light. Credit: Simon Gilroy/University of Wisconsin-Madison/YouTube
Schlanger explores why scientists have missed fundamental ideas about plants – as many Native cultures have treated them as relatives, ancestors, or simply creatures in their own right. Schlanger covers not only these Aboriginal philosophies, but also how the influences of the European thinking of Aristotle and René Descartes led to treating living things as mechanical and passive. Although botanists use very pleasant language in conversations, in their research papers they describe the behavior of plants using the passive voice. “The plant does not ‘react,’ rather it is ‘affected,'” as Schlanger points out. “Exposing these processes without calling the agency is actually difficult, obviously, wrong.”
The realization that plants are not just a collection of cells, but are intelligent people, perhaps even worthy of being human – which means “man has a choice, and has the right to exist because of them” – has great moral, philosophical, and policy implications. Several legal debates in recent years have dealt with the humanity of plants and ecosystems threatened by human activities. “When do plants enter the gates we look through?” Shlanger asked. “Is this when they have a language? If they have family structures? If they make alliances with enemies, have favorites, plan ahead? When we find they can remember? They seem, indeed, to have all these characteristics. Now we have chosen to let that truth in.”
Schlanger repeatedly exposes the wide gap between society and scientists when dealing with the question of plant intelligence. For example, Monica Gagliano, a botanist in Australia, has become a “disputed figure” in her field because of her strong stance on studying the ability of plants to feel – and using her method of understanding and rigor based on evidence. “He speaks to packed audiences at philosophical conferences and public science events,” Schlanger writes. At the same time, he is no longer funded by traditional government grants, but instead by the Templeton World Charity Foundation.
Readers who loved the book “The Secret Life of Plants” may be happy to learn that this book has directly harmed the scientists they wanted to help. “The great characteristic of science and the greatest beauty is that it almost always errs in admitting the truth,” Schlanger wrote. Questions about the intelligence of plants may even cause a spiritual and moral problem within science, a paradox in which the historian Jessica Riskin of Stanford University wrote: “The dismissal of the seventeenth century to work, to see, to know, and to natural will and natural science gave. to reign in all these attributes to an external god.” Early scientists avoided these topics because this view of nature was compatible with the religious views of the time. “They left their heirs with a problem that continued to work three centuries later.”
An affirmative plant center can rid science of this relic of the past and, Schlanger bets, bring a new perspective, one that unites nature and people and acknowledges the agency of all life. “Plants will continue to be plants, whatever we decide to think about them,” Schlanger noted. “But how we decide to think about them can change everything for us.”
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