The Light Eaters
A Book Review
“Burning with open-minded curiosity, this exploration of the emerging revolution in plant science will challenge what you think you know and ignite a new way of seeing. …I feel it as an antidote to arrogance, as it engenders humility, respect, and awe for the light eaters who make the world.” —Robin Wall Kimmerer, author of Braiding Sweetgrass
Dick McBride
Zoë Schlanger’s Journey into Plant Science
Recent research is quietly changing our understanding of plants and may completely alter how we think about life itself. A scientific disaster unfolded with the publication of The Secret Life of Plants in 1973—a beautifully written collection of myths suggesting physical, emotional, and spiritual relationships between plants and humans, rooted in “New Age” notions. This specious approach discredited serious work in botany, and funding for plant research dried up for years.
Zoë Schlanger, an environmental reporter, spent years covering climate change and environmental disasters. Eventually, she became numb from reporting so much bad environmental news and searched for something more enlightening. She found herself drawn to botany journals filled with discoveries about the plant world. Thanks to advances like DNA sequencing and improved microscopes, plant science was slowly recovering from the damage done by The Secret Life of Plants.
Schlanger became fascinated with plant behavior and decided to share her findings and reflections in this book. She explores the idea of being in and of nature—alert to its presence. Thinkers like Alexander von Humboldt, the 18th-century naturalist, believed that being outside in nature evokes something existential and real, something that speaks to the soul. Nature offers a sense of wholeness, but where do plants fit within this framework? How do we relate to them? If nature is chaos in motion, then what is a plant? We live surrounded by plants, yet we understand so little about them.
The Question of Plant Consciousness
Schlanger consulted numerous scientists while writing the book. Talking about plant sensing was generally acceptable. And talking about plant behavior was riskier territory. But talking about plant intelligence was outright dangerous. The debate over plant intelligence remains contentious, largely due to disagreements about word choice. Science is a conservative institution, but it has no agreed-upon definition for life, death, intelligence, or consciousness.
Measuring plants against human cognition makes little sense; it sets them up as lesser beings, as if they exist on some hierarchical scale beneath humans and animals. But plants have senses that, in certain ways, far surpass our own. They shape our biology, culture, and ecosystems as profoundly as bacteria and fungi, which are similarly ignored.
How Science Changes Its Mind
Most people can tell the difference between dog breeds but suffer from “plant blindness”—the tendency to view plants as an indistinguishable mass rather than as thousands of genetically separate and fragile individuals. But as Schlanger reports, new research suggests that plants may have a form of intelligence. Ferns can release hormones that slow down the sperm of competing ferns to give them an advantage in reproduction. Plants can recognize their own kin, summon insects to attack predators, and can even hear water flowing in pipes. Other plants can detect the saliva of predatory caterpillars and can make compounds that attract the exact wasps needed to attack those caterpillars.
Schlanger believes we are standing on the precipice of a new understanding of plant life. Plants were universally thought not to have consciousness until the mid-19th century. After The Origin of Species, Darwin devoted almost all his time to plants, making and publishing many observations. One of his last publications about plant movement reported on a “cuticle” at the tip of a root that seemed to be a “command center”—a plant brain. This idea was rejected for well over 100 years. Scientific paradigms can last a long time but can change quickly if new information comes along.
Our current understanding of plants is rudimentary, but we already know that plants can form, store, and access memories; sense incredibly small changes in their environment; and send highly sophisticated chemicals aloft to affect their surroundings. They send signals to different body parts to coordinate defenses.
Schlanger suggests we don’t need new words for the behaviors that are similar to ours, just prefixes: plant brains, plant synapses, plant thoughts (see the Society of Plant Signaling and Behavior). She challenges us: can consciousness be a transcendent, free-floating property of the universe? Rethinking plants could change everything for us.
The Communicating Plant
The book is loaded with examples of ways in which plants communicate to other plants and to animals through elaborate exchanges of chemical signals. Plants bitten by bumblebees can bloom as much as 30 days earlier. Goldenrods can sense the volatile signals of gall-forming flies and jump-start their immune systems. Myrmecophytes are plants that feed ants, which will then attack the plants’ predators. We all know that legumes house nitrogen-fixing bacteria in their roots. Plants are geniuses at synthesizing chemical compounds—sending them through the air or into their roots to accomplish a myriad of tasks, communicating with their environment.
The Chilean vine Boquila can morph to match the leaves of neighboring plants—mimicking their shape, color, texture, and vein structure. Some mistletoes can do this too. The mechanism remains a mystery. Some suggest airborne cues or horizontal gene transfer; others wonder if plants can “see.”
Eusocial behavior—where individuals prioritize the group’s well-being—also appears in plants. They interact with their neighbors daily and can recognize siblings. Light cues help them “see” one another. In crowded environments, they grow taller; in sparse areas, they grow shorter.
Sunflower growers found that planting sunflowers in tight rows improves yield. The plants angle their stems to avoid shading each other. Kin recognition suggests social awareness and decision-making. Plants and fungi have co-evolved for eons, forming mutually beneficial relationships.
Plant Intelligence and the Futures
There are some plant biologists today advocating for “plant intelligence,” feeling that intelligence is probably a property of all living things. It should be noted that many don’t feel that way. These biologists appreciate the resourcefulness of plants, their ability to adapt to changes, and the resiliency of their stem cells.
A major leap in human knowledge has taken place, with animals of all types being found to have language, literature, and art. We now know that plants do speak with chemicals, and communicate with one another and members of other species when the situation calls for it. Science may never fully arrive at the conclusion that plants are intelligent—at least in the way the word most readily applies. Plants are far more advanced than humans in multiple categories, such as producing complex chemicals like caffeine. Comparing plants to humans erases their capabilities.
New findings in botany are revealing opportunities to remodel our understanding of the nonhuman world and our place in it. But plants are not just like us. Understanding them requires embracing ambiguity—complexity is a rule of nature. Seeing plants as “beings” (my quotation marks) worthy of rights could revolutionize our moral system, legal system, and the way we live on Earth.
A Final Thought
This book and its vast array of plant observations have affected me deeply. All life likely shares a common origin, evolving into the millions of species we know today. Homo sapiens is just one. Our ability to communicate with other species remains limited, but what if one day farmers could use sound to help plants defend themselves—eliminating the need for pesticides.
Schlanger mentions the science fiction novel Semiosis, in which humans land on a planet a billion years older than Earth—dominated by plants with a massive evolutionary head start. Eventually, humans and one plant species must team up to survive.
I’ll leave you with this: Schlanger shares the story of the green sea slug, native to the Atlantic Ocean off the U.S. East Coast. It begins life as a brown creature, but after feeding on green algae, it absorbs the chloroplasts and turns bright green. After just a few feedings, it no longer needs to eat—photosynthesis sustains it. This is a real phenomenon.
The Light Eaters is full of moments like that, moments that can change how you see the world. Maybe, Schlanger suggests, we are on the edge of something bigger—an understanding of life that’s been in front of us all along, hidden in the leaves.