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The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth
Schlanger, Zoë

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Each creature is folded into layers of interrelationship with surrounding creatures that cascade from the largest to the smallest scale. The plants with the soil, the soil with its microbes, the microbes with the plants, the plants with the fungi, the fungi with the soil. The plants with the animals that graze on them and pollinate them. The plants with each other. The whole beautiful mess defies categorization.
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Complexity lives at every scale.
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The more botanists uncovered the complexity of forms and behaviors of plants, the less the traditional assumptions about plant life seemed to apply. The scientific field was eating itself alive with contradictions, points of contention multiplying as fast as the mysteries.
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We determine intelligence in ourselves and certain other species through inference—by observing how something behaves, not by looking for some physiological signal.
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Others go farther, suggesting that plants may be conscious. Consciousness is perhaps the least understood phenomenon in human beings, let alone other organisms. But a brain, this camp says, may be but one way to build a mind.
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Plants, after all, are their own clade of life, with an evolutionary history that swerved away from our own long ago.
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they sense things we can’t even imagine, and occupy a world of information we can’t see.
Chapter 1: The Question of Plant Consciousness
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I’d explain the latest IPCC report—the ones telling us we had very few years to stave off catastrophe—to my colleagues with an eerie sort of glee, awaiting their paled faces. I’d often spend a morning ingesting news about record-breaking wildfires and hurricanes and pivot seamlessly to office gossip by lunch. The compartmentalization became so total that I could no longer muster any emotional response to environmental cataclysm. Melting ice sheets in Greenland started to look like just another good story.
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specialized pocket in its body to house a packet of cyanobacterium that fixes nitrogen. The air around us is nearly 80 percent nitrogen, and every life form, including ours, needs it to manufacture nucleic acids, the building blocks of all life. But in its atmospheric form, it’s entirely out of our reach.
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plants rely wholly upon bacteria that know how to recombine nitrogen into forms the plant—and all of us who get our nitrogen from plants—can use.
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Humboldt went on to introduce the European intellectual world to the concept of the planet as a living whole, with climatic systems and interlocking biological and geological patterns bound up as a “net-like, intricate fabric.” This was Western science’s earliest glimmer of ecological thinking, where the natural world became a series of biotic communities, each acting upon the others.
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that plants could be thought to behave at all was still an enchanting possibility.
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a nine-year-old girl, especially not one who truly believed she was an adult trapped in a child’s body. Which is to say I was alone and predisposed to fantasy. Girls of that nature tend to build complex internal worlds that they proceed to drape like a blanket over the world around them. Adults who don’t understand this disposition tend to call it melodramatic.
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was sure I was simply seeing things around me for what they actually were. In most cases, those things were trees and squirrels and sometimes rocks, and they were very much alive, alert to the world. Children are known to be inborn animists.
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There has always been an extreme tendency in popular culture to layer simple human narratives on other species, as seen in virtually every fairy tale or animated film.
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Making the mental space to imagine truly different intelligences, without jumping to easy human conclusions, is a difficult task.
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Over and over, I saw the debate framed as a dispute over syntax. But it looked to me more of a dispute over worldview. Over the nature of reality. Over what plants were, particularly in contrast to ourselves.
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Nature is not a puzzle waiting to be put together, or a codex waiting to be deciphered. Nature is chaos in motion. Biological life is a spiraling diffusion of possibilities, fractal in its profusion. Every organism, and certainly every plant, has ricocheted out of another fragment of the evolutionary web of green leafy things to variate further. These each are of course still morphing, because that sort of thing never ends, except in extinction.
Chapter 2: How Science Changes Its Mind
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The plant cells that today catch photons as they fall from space are themselves chimeras in miniature; that first cyanobacteria is still within them, still faithfully alchemizing light into food.
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A leaf is the only thing in our known world that can manufacture sugar out of materials—light and air—that have never been alive. All the rest of us are secondary users, recycling the stuff the plant has made.
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Through that encounter with the pure energy of light, the water and carbon dioxide molecules are ripped apart. Half of the oxygen molecules from both parties float away from this meeting, passing back out into the world through the parted lips of the stomata—becoming the air we breathe. The carbon, hydrogen, and oxygen that remains is spun into strands of sugary glucose.
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Perhaps a plant’s biggest achievement is its anatomical decentralization. A plant is modular; snap off a leaf, and it can grow a new one. Without a central nervous system to protect, the plants’ vital organs are distributed and come in duplicates. That also means a plant has evolved remarkable ways to coordinate its body and defend itself. They might grow thorns and spikes and stinging hairs, developed with remarkable precision, to pierce the flesh or exoskeleton of whatever mammal or bug might be its main threat. They might secrete sticky sugar to entice and then immobilize their antagonists, whose hungry mouths get stuck shut. Their flowers might be extra slippery, to deter nectar-thieving ants. Whatever the adaptation, it tends to be economical in its specificity. There’s a purpose to every tiny variation. This is true for all areas of plant physiology; every part of the architecture of a plant’s body is there for a reason, calibrated to fit its task. No more, no less.
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Plants are themselves synthetic chemists, surpassing the best human technology in terms of the subtle complexity of the chemicals they can synthesize.
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“No part of the aim of normal science is to call forth new sorts of phenomena; indeed those that will not fit the box are often not seen at all,” Kuhn wrote. A paradigm can’t ask questions about something it doesn’t see as existing in the first place. The resistance by scientists to scientific discovery is a known fact; it serves as a bulwark against quackery. But it also often misses or delays actual discoveries. The recognition of something as a significant anomaly that needs explaining—as Ian Hacking put it in his introduction to Kuhn’s book—is a “complex historical event.” And even that is not enough to prompt a scientific revolution. There must be another paradigm to accept before a rejection of the first can take place. “To reject one paradigm without simultaneously substituting another is to reject science itself,” Kuhn writes.
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They named themselves the Society for Plant Neurobiology. František Baluška, a cell biologist at the University of Bonn, Elizabeth Van Volkenburgh, a plant biologist at the University of Washington, Eric D. Brenner, a molecular biologist at the New York Botanical Garden, and Stefano Mancuso, a plant physiologist at the University of Florence, were among the founding members. Our understanding of plants is still so crude as to be rudimentary, they said. “New concepts are needed and new questions must be asked.”
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Plant neurobiology “aims to study plants in their full sensory and communicative complexity,” they wrote. And what is a brain, really, other than a hunk of specialized, excitable cells, coursing with electrical impulses?
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a plant is a multidimensional organism in constant biological conversation with its surroundings, the bacteria, fungi, insects, minerals, and other plants that make its world. It is no wonder then that zoologists and entomologists have been the ones to make some of the most groundbreaking discoveries about plants, often by viewing them through the lens of animals and insects.
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in an age where genetics dominate, many have ceased to see the plant as a pulsating whole, and instead see it as an amalgam of genetic switches and protein gates.
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The Society for Plant Neurobiology eventually backed away from their provocative name; they became the Society of Plant Signaling and Behavior. Yet even the word behavior still caused some botanists to prickle.
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the octopus, with its brain-like arms, the neurons distributed throughout its body. We are just beginning to imagine what the world looks like to them. There’s no doubt it looks entirely different than it does to us. There is also no doubt that their distributed neuronic substrates are part of what gives them the capacity for such intelligent behavior, as well as the distinction of consciousness we have so recently deigned to bestow upon them.
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the idea that decentralized networks built by fungi and slime molds can be intelligent, and perhaps even more agile in their ability to react to new challenges precisely because of their diffuse nature.
Chapter 3: The Communicating Plant
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The beard lichen that clung to a white birch beside me looked as though it had slinked with great purpose up the young tree, sheathing its trunk like a tube sock. It was advancing scruffily too along the lower branches. I had the dreamlike sense that it had cunningly frozen in place just in time for my glance. Lichen time is slower than human time, so I supposed it had—it and all its brethren, in motion but frozen in our moment of notice.
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The language of scent, they said, was wafting messages on the air. I began to understand that a many-layered drama was playing out all around me, with more characters and plot lines than a Russian epic. Some of these I could smell, and there were many more my nose was too naive to notice.
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For life to open to the possibility of multicellularity, individual cells had to coordinate among themselves. Up to that point, all life was single-celled. These autonomous little selves were adrift in the ancient sea, each making their way on their own. For more complex forms to emerge, individual cells had to share information with each other.
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In 2017, researchers at the University of Birmingham identified the presence of a “decision-making center” within dormant seeds that integrated information and decided when the plant should emerge. This center is made up of a cluster of cells located at the tip of the seed’s embryonic root. The cells communicate to each other about the abundance of two hormones in the seed; one hormone that promotes dormancy, and one that promotes germination. The cells integrate information about the changing temperature of the soil around them to regulate each hormone. In this way, the cluster of cells decides when to flip the switch and emerge into the world. The timing of the decision to emerge is critical. This risky decision is made more accurate by relying on the cumulative responses of multiple cells; by making a decision based on two opposing variables—the relative abundance of two hormones, both of which are sensitive to temperature changes—the plant has a higher chance of making a good choice in a fluctuating world. This is, the researchers noted, a method of cell-to-cell communication analogous to certain structures in the human brain. Our brains also pass antagonistic hormones back and forth between cells to improve our decision-making in a fluctuating world. Rather than making the decision to move a muscle based on a single input, the brain makes its decisions by accumulating hormonal information from separate cells, and weeding out irrelevant information in the process. This is at its heart a case of cells in communication.
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Through the chatter of their cells, plants are self-organizing systems. But that whole plants might be considered to communicate intentionally with each other—that communication could extend beyond one plant to others—is a relatively new and still controversial concept in botany.
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Intentionality is more difficult to discern, in part because we don’t know what it’s like to be a plant. Intention poses the hardest of problems, because it cannot be directly discovered. We can only build knowledge around the problem of intention, drawing our perimeter closer to it, and hope that in encircling it, its form might begin to take a shape we can understand.
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a tree without leaves to photosynthesize in the growing season cannot make sugar and effectively starves to death.
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plants operate on a slower timescale than insects, so it made sense that they’d react more slowly too.
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Plants are tremendous at chemical synthesis, he knew. And certain plant chemicals drift on the air. Everyone already knew that ripening fruit produced airborne ethylene, for example, which prompts nearby fruit to ripen too. The commercial fruit industry used it to ripen warehouses full of unripe bananas just in time for sale, making the global trade of an otherwise fast-rotting fruit possible.
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Jack Schultz spent decades as a major contributor to the field of communication between plants and insects, and was known to say that the scent of cut grass is the chemical equivalent of a plant’s scream.
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Nature, never a flat plane, has always more folds and faces still hidden from human view. The world is a prism, not a window. Wherever we look, we find new refractions.
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goldenrods that live in peaceful areas without much threat from predators will issue chemical alarm calls that are incredibly specific—decipherable only to their close kin—on the rare occasion they are attacked. But goldenrods in more hostile territory signal to their neighbors using chemical phrases easily understood by all the goldenrod in the area, not just their biological kin. Instead of using coded whisper networks, these goldenrod broadcast the threat over loudspeaker, so to speak. It is the first time research has confirmed that these sort of chemical communications are beneficial not only to the plant receiving them but also to the sender.*
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Sagebrush also use “private” means of communication to warn only their family groups about insect attacks when the threat from bugs was generally low. Basically, they are using backchannels—the chemical compounds they use are complex and specific to them and their closest allies. But when the whole community is being heavily attacked, sagebrush will switch to “public” channels, emitting more universally understandable alarm calls. This tracks perfectly with something that has been known about songbirds for a long time. In peaceful places, where relatively few dangerous predators lurk, birds use extremely specific song phrases to warn only their family group that something is wrong. But when the birds are facing widespread danger, they switch calls, making alarm sounds that everyone in the area can understand, even members of other bird species. This makes sense, again, in terms of community survival; when the whole neighborhood is threatened, it’s best to save as many of your kind as possible, regardless of if they’re family or not.
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plants could be said to have dialects, and are alert to their contexts enough to know when to deploy them. More than that, they have a clear sense of who is who; who is family, and who is not. They are in touch with their surroundings, and with the fluctuating status of their enemies. Their communication is not just rudimentary but complex and layered, alive with multiple meanings.
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I would spend an eerie moment contemplating my house plants; were they being silenced? Are these companions who make my apartment feel more alive being deprived of some essential plantness? It seemed likely now. First of all, they were in pots. When it came to root-to-root communication, they were undeniably cut off from any connection to their fellow plant life—not to mention the network of fungi and bacteria they might normally associate with. But were they also cut off from the chemical form of plant speech? Did they breathe meaning into the air through chemical compounds, the way their wild counterparts almost certainly do? Almost all of the plants in my apartment were tropical varieties widely cultivated in nurseries. So far from their wild ancestors. Were these plants some diminished, domesticated version of their wild relatives, so many generations removed from the jungles of their kind that they forgot how to speak, perhaps never hearing their language? And lineage aside, was I now keeping them like animals in cages, confined, muted, in their pots? It was chilling to imagine. Or were they more like dogs to wolves, in need of my care, now that they’d lost the context for and traits of total self-sufficiency? I didn’t know how to feel about that either. It was also, I knew, a flight of fancy. I’d probably let my mind travel too far. It’s very easy to do that when thinking about plant agency. Yet—I scolded myself now, confusing things further—what is “too far” when the topic at hand is the agency of living creatures?
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In 1840, when a German chemist named Baron Justus von Liebig published a monograph breaking down the three main elements plants need for growth, he also demystified soil fertility, which had long been an enigma. Within a few decades those three elements—nitrogen, phosphorus, and potassium—became the basis for the modern synthetic fertilizer revolution, which permanently changed the practice of farming. Since then, however, we’ve come to understand that plant health is far more complex, and that the relentless use of synthetic fertilizers can in fact do indelible harm to ecosystems and soil fertility in the long run. New layers of soil complexity have more recently come into focus, involving interspecies relationships between untold numbers of microbes and fungi.
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given the economics of modern agriculture, which values yield above all, many of the world’s food staples continue to be grown in vast, undifferentiated fields. The crops tend to be bred for productivity above anything else, often at the cost of other traits, like the ability to defend themselves. As such, huge quantities of pesticides and fertilizer are often needed to sustain them.
Chapter 4: Alive to Feeling
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Electricity is entangled in every aspect of our living. It is behind our ability to move, think, breathe. It doesn’t have a pulse, but a pulse has it; or, rather, electricity is the reason for the pulse at all. What to call something that on its own is not quite alive, but surely not inert either? The theorist Jane Bennett calls it vibrancy. That appeals to me. Electricity has its own vibrancy. It makes us happen.
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From a certain perspective, a plant is a sack of water—or slightly more specifically, a skinlike sack of cells, each inflated by a coursing watery liquid. (Same with us, by the way.) That arrangement makes plants extremely electrically conductive. Electrical pulses move through the plant body very fast. But could plants be using that electricity to understand and react to the world, like we do? To move, grow, send messages to their distant parts? Whereas most electrical impulses in our body are routed through our brains and spat back out as information, plants have no such recourse. So how in the world would electricity be a means of signaling, making meaning out of inputs, without a brain?
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an idea that verges on the mystical. Or at the very least, it verges on an entirely new conception of life—which so often starts out sounding like mysticism, doesn’t it?
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In the human body, electricity works like this: the membrane potential of our cells, when at rest, is ever so slightly negatively charged. Positively charged elements—sodium, magnesium, potassium, and calcium ions—are afloat in the plasma between those cells. These are your electrolytes. When touched, the cells open channels in their membranes and allow these ions to pass through them.
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Suddenly, with the influx of ions, the cell’s charge flips from negative to positive. This produces a burst of electricity known as an action potential. That sudden burst triggers the ion gates in the neighboring cell to open too, electrifying that cell in turn. This chain reaction travels fast, sending information via the electric current that the bestirred cells make from your finger (and cheek) to your brain and back again. Almost all our cells are capable of generating electricity.
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the smooth muscle around our veins, which contracts and releases to keep the blood flowing through our body. Our brains, of course, are fantastically electrical,
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Touching an anesthetized person’s body—or cutting them open with a scalpel—will not produce the same flurry of electrical bursts it would under normal circumstances. The drugs interfere with our action potentials.
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A wave is a very good way to transmit biological information. Slime mold instructs its own movement by sending wavelike pulses through its body, which is itself a single giant cell packed with many thousands of nuclei.
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Once one leading edge of the slime mold has picked up the scent of nearby sugars and proteins, it softens the nearest part of its gelatinous form, causing the fluid in its body to bulge forward in that direction. The rebalancing of fluid causes the entire sack of the giant cell‚ numerous nuclei and all, to ripple in a wave, propelling its gelatinous body forward in the direction of the food. Likewise the slime mold can pulse with tiny contractions, sending waves through its fluid body to rapidly send signals to far-flung parts of itself, making its coordinated behavior possible.
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Mycelium, the ubiquitous underground body of fungi, may coordinate its millions of individual threads by way of waves of electricity. In this way, information about moisture and food can travel throughout a mycelium whose hairlike tentacles might form a mat spanning a hectare of forest floor.
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When touched, a plant will essentially activate its immune system.
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Most plants don’t appear bothered when we step on them or pluck a flower. But we now know they bristle internally with all the force of a startled porcupine or a spooked stallion. Plants are fully aware of our contact with them, and will rearrange their lives to respond to such treatment.
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J. C. Bose, as he was known, was the pioneer of wireless telecommunication, having discovered millimeter-length electromagnetic waves—the microwaves that made the first radios possible and are used in remote sensing and airport security scanners today. In fact, he built the radio wave receiver used by Guglielmo Marconi to make the first working radio. He was perhaps the most famous biologist of his generation;
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photosynthesis is an inherently electrical process.
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the flow of electric current—essentially, calcium ions—
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“Voltage-activated ion channels are the basis of nerves.”
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Van Volkenburgh found that the recent onset of the genetics revolution had made it impossible to get funding for her work on electrical responses in plants. “Everything shifted to genetics,” she said. Genes were in, electrophysiology was out.
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Funders preferred the clear-cut nature of finding patterns in genetic codes.
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plant electricity is now blooming into a substantial field of its own, spurred on by improved tools and the slow fade of a now tired taboo, a relic of a more paranoid time. Scientists are resurrecting some of that early electricity research from the days of J. C. Bose, but doing it with better tools.
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The inside of each trap bristles with a few flexible spike-like hairs. Insects, lured by a sugary aroma, brush against the hairs while looking for nectar. In 2016 researchers discovered that these hairs are mechanosensory switches that elicit action potentials, and that the flytrap can actually count how many action potentials have been triggered;
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Most recently, they had been developing a theory of agency for plants. Gilroy was quick to remind me that he was talking strictly about biological agency, not implying intention in a thoughts-and-feelings sense. I nodded, and he continued. “Plants, in the timeframe we think of animals operating, do very similar things to animals as far as information processing. They make very complicated calculations about the world around them. It would be incredibly impressive if a human being did that sort of information processing and came to the output that the plants come to.” Plants make their lives work in the environment they find themselves in. That, for him, is proof of their agency. Still, the proof is through inference rather than understanding the mechanics.
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plants did that. They made the terrestrial world a habitable place for other forms of life to arise, and eventually to be able to breathe. Without them, animal life as we know it would not even have had the faintest shot at clambering onto the evolutionary treadmill.
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in humans and many other animals, the way we perceive gravity is understood: in our inner ear, we have canals angled at 90 degrees to each other. The canals are lined with trigger hairs, much like those inside Venus flytraps. The canals are also full of liquid in which crystals are suspended, like glitter in a snow globe. As we bend or turn, those crystals fall down with gravity, settling onto some of the trigger hairs. The hairs bend under their weight like a pin struck by a pinball, sending electrical signals to our brain, which tells us which direction is down. (If you spin around and stop, and the world still seems to be moving, it’s because the fluid in those canals is still moving, as if the snow globe was given a good shake. The pinballs are hitting all the wrong pins. The spinning will stop when the ear confetti settles again.) But the key here is that the electrical signal is sent to our brain. Only then does that information turn into something our bodies understand.
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Calcium is not, in itself, a form of information. It’s basically the footprint left behind by electricity, a kind of “second messenger.” In animals, calcium levels increase in a cell when ion channels open. Ion channels open when electricity is passing through. So calcium shows up in a cell directly after the electricity does.
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The technology for visualizing calcium in plant cells was dreamed up years ago. It worked like this: researchers took the gene responsible for making green fluorescent proteins out of a species of jellyfish that glows naturally in dark water, and engineered it to be responsive to calcium. Then they inserted the gene into the chromosome of a plant—the part of the cell responsible for passing genetics on to the next generation. When a gene is inserted into the chromosome, it duplicates itself in every cell of that organism’s offspring. That means that every future seed that plant produces will make a baby plant with the capacity to glow green already built into each of its cells. Intriguingly, virtually all organisms have the capacity to run the same bit of jellyfish DNA. “The genetic code in the jellyfish is universal,” explained Gilroy. “You can take the code and put it into any other organism you want, and it will work the same.” Even people? I pictured a person with a faint green glow coursing through their musculature. Gilroy laughed. “Hypothetically you could do it to people. Ethically you could not.”
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all living beings respond very quickly to the world around them. Because if they don’t, they aren’t going to be living for very long.”
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Whenever you’re talking about electrical signaling in cells, you’re talking about ions moving across the cell membranes. Electricity in a body always begins with chemistry of this sort.
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We know electrolytes are important for conducting electricity; humans use mostly potassium ions as their electrolytes, and plants use mostly calcium ions.
Chapter 5: An Ear to the Ground
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Plants and insects interact all day long, and at every stage in both of their life cycles. It may be the most important relationship in either of their lives, if the insect is the type that drinks nectar or eats leaves, which is to say the great majority of them. Plants and insects together make up about half of all multicellular organisms on earth; it wouldn’t be an exaggeration to say theirs is one of the most important relationships on the planet.
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the tiny hairs on arabidopsis leaves function as acoustic antennae, picking up and vibrating at the frequency of incoming sounds. Many other plants also have tiny hairlike structures on their leaves; understanding whether or not these structures, called trichomes, function as antennae on other species too will require more study. Researchers have already found that trichomes allow plants to sense the footsteps of moths and caterpillars, and mount defenses in response; trichomes are clearly exquisitely sensitive organs.
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it was Gagliano’s 2018 memoir, Thus Spoke the Plant, that put her reputation over the edge. In it she describes taking ayahuasca in a shamanic ritual in Peru and communing with the spirit of the plant, who told her how to best design her studies. In science there is a tacit separation of church and state. Purity in science means not wading into mystical waters, or at least, if you do, keeping it to yourself.
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arise which proved to her colleagues that her discovery was true. Perhaps scientists should be more open to losing their grip on the rationalist certainties that sustain their careers, posit Onzik and Gagliano.
Chapter 6: The (Plant) Body Keeps the Score
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it occurred to me that memory must be the basis of all complex behavior. I’d learned about plants listening to their surroundings, feeling touch, and exchanging information. But each of these abilities were limited by their fleeting temporality. What good is all that sensation without the ability to remember it? Without memory, very little can be done intelligently. Memories give us the capacity to learn, and to orient ourselves in time and space. What would it mean if a plant could remember? Not the genetic sort of memory, of birds returning to the same migratory grounds each year, but individual memory. Elastic memory. Memories that change when circumstances do.
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What the garlic needs, in order to sprout, is the memory of winter. That the spring eventually comes is not enough to make life emerge—a good long cold is crucial. This memory of winter is called “vernalization.”
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because animals have always needed to move over a wide terrain to find food, animal evolution “refined sensory and motor equipment and joined the two with a rapid connection,” to eventually be joined by nerve cells “compacted into a brain.” Can you build a mind from something else? Brains, after all, came into being via evolution, emerging from nonmental ingredients.
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consciousness so far has proved impenetrable to modern neurobiology. The fact that a brain produces the experience of “mind” is not explained by its mere physical existence.
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“The individual plant containing many millions of cells is a self-organizing, complex system with distributed control permitting local environmental exploitation but in the context of the whole plant system,” he writes. “Consciousness is thus not localized but is shared throughout the plant in contrast to the more centralized location in the animal brain.”
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Human spatial memory is our keenest form of memory,
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Our brains are centralized and compact, perfect for animals that must travel and take their wits with them. What if instead of hunting, our food was sunlight that rained down on us, so we were bathed in it, and we had to evolve only to be prepared to receive it? Instead of a compact and portable brain, we might instead have evolved a limitless ability to build new arms covered in mouths on short notice.
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Our private collections of experiences grant us our sense of ourselves, the sense of our own subjectivity that we come to view as consciousness. A more generous view of plant life might extend to them some measure of that same subjectivity; they do, after all, seem to experience and remember their world as they move through it. Mysteries abide, of course. We are far from understanding the extent of memory in plants. We have a few clues and fewer answers, and so many more experiments still to try. But new threads of relation extend between us. A universe of selves comes into focus.
Chapter 7: Conversations with Animals
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the relationships plants have with other plant species, and even with animals, is a tapestry of dynamics that run the gamut from reciprocal to exquisitely antagonistic.
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Bittersweet nightshade, a plant in the same family as tomatoes, potatoes, and tobacco, secretes sugary nectar in order to recruit ants as bodyguards. The ants, hooked on the sticky syrup the plant oozes for them, dutifully pluck off the larvae of the bittersweet’s mortal enemy, the flea beetle, which are clinging to the plant’s stem. They must be quick, before the wriggling flea beetle babies have a chance to bore themselves into the bittersweet’s body and wreak havoc. The ants march the larvae deep into their ant nest. The larvae are never seen again.
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Semiochemicals are any compound that is synthesized in one body and released to infiltrate another. They are by definition any chemical one creature makes and exudes to take the reins of another creature.
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All flowers are basically billboards to attract pollinators.
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they described plants’ biochemical synthesis as a “language,” with the various complex combinations of compounds as the plants’ “vocabulary.” The combinations and proportions of the compounds in the bouquet, they wrote, could be described as “sentences.”
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The pollution steadily filling the air appears to sabotage plants’ ability to send and interpret each other’s signals.
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questions about whether fields planted with highly engineered plants grown in vast identical plots for food, like the corn, have had communication unknowingly bred out of them. Or perhaps it has been rendered unnecessary by the hand of selection for a plant that is given everything it needs to survive without endlessly defending itself.
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strawberry flower is self-fertile; it can produce fruit using its own pollen, or essentially by having sex with itself. It also can cross-pollinate with other strawberry plants, though this requires the help of flying insects. Farmers know that strawberries will produce a third more fruit—and much of it higher quality—when planted beside borage, a medicinal herb that blooms in perfect blue stars. The borage attracts the strawberry’s pollinator; the better, more copious berries emerge when the sexually adaptive strawberry opts to copulate by way of insects rather than with itself.
Chapter 8: The Scientist and the Chameleon Vine
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Some vines coiled around objects to hoist themselves up, others secreted sticky adhesive, yet others grew tiny hooks to secure their ascent. And all of them located their scaffolding by way of slowly revolving their growing tips in a circle through the air until they bumped into something solid.
Page 164 · Location 2569
If plants can be knocked unconscious, does that make them conscious? Baluška says absolutely. “I think consciousness is a very basic phenomenon which started with the first cell,” he says. And besides, what is consciousness but the ability to handle situations, to take care of yourself? “If you are not conscious, you are not aware of your environment and you cannot act. You are out. If someone is taking care of you, you can survive, but you alone cannot survive.”
Page 165 · Location 2592
Crop science is typically seen as the domestication of scrawny wild species to turn them into plump, useful food machines, a testament to human will and ingenuity. But Baluška objects to it being true “domestication” at all. “Domestication would be when one partner has more influence than the other one. But there is no evidence for this,” he says. “A better word would be coevolution. We are changing them, but they are changing us.”
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A fleet of humans carefully tending a field of crops can certainly start to look like an army of plant symbionts, diligently serving the plants’ needs.
Page 167 · Location 2621
Recent research suggests that an ancient cyanobacteria, an early ancestor of plants, had (and still have) the smallest and oldest example of a camera-like eye.
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Vision is fundamentally the perception of light and shadow. Objects become visible to us and other animals when they reflect light back to us. Color, too, is a basic trick of light: it emerges when an object absorbs certain wavelengths of light but not others, reflecting those back to our eyes, determining the color we see it as. Green leaves, for example, appear green because they absorb red and blue wavelengths, returning to our eyes only the green. Chlorophyll in the plant eats that red light to convert the CO2 and water it absorbs into sugary food; this is photosynthesis. Light includes a spectrum of colors, some visible to us and others beyond our visual spectrum; picture the rainbow that a prism, which splits the light waves, can cast on your wall. When light passes through the green flesh of plants, the plant absorbs some of the red light in the spectrum for photosynthesis, so the remaining light that passes through the plant will contain less red light once it gets to the other side. That means the light that has passed through a plant will have a different ratio of colors; specifically, the ratio of red to far-red light wavelengths—a form of red light on the very extreme edge of our visual spectrum—is reduced.
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plants don’t just have receptors for red light. Botanists have thus far found fourteen types of light receptors in plants, each of which contribute vital information; some allow a plant’s shoots to grow toward light, and others help it avoid damaging UV rays. But many of the photoreceptors remain unexplained.
Page 182 · Location 2867
In the 1990s, researchers discovered units of genetic material called “small RNA,” or sometimes “micro RNA.” They originate in microbes like bacteria and viruses, and as of now 2,600 distinct types of micro RNA have been discovered in the human body. It is believed that these bits of foreign genetic material collectively regulate as much as one-third of the genes in our genome.
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the most signature behavior of termites—wood-eating—is made possible by entirely different organisms living within them. The termite’s gut microbes, in turn, are able to function thanks to yet smaller microbes that live within them.
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termite is never just a termite. The same is clearly true for every organism. “What you thought was managed or the result of the action of this organism,
Page 185 · Location 2911
Rupert Sheldrake’s concept of a “morphogenetic field.” I hadn’t. He explained that Sheldrake imagined a hypothetical biological field surrounding every organism, like a cloud of information. “It’s a type of field of influence,” he said, invisible but potent, like a gravitational or magnetic field. The morphogenetic field, as Sheldrake conceptualized it, directed the development of an organism’s physical form. I pictured clouds of information encircling the plants all around us, plumes of biological instructions.
Page 186 · Location 2928
The recent torrent of microbiome research has revolutionized our understanding of how we interact with the world, as scientists draw connections between all manner of health issues and the creatures living in our guts and on our skin. Our microbes influence our immune systems, our smells, and our attractiveness to mosquitoes. Emerging research suggests they may play a role in autism, depression, anxiety, and possibly even who we are attracted to.
Page 187 · Location 2948
The way the “self” is described in Vipassana, a form of Buddhist meditation, is as a collection of tiny, quivering units. Some call them atoms. At the root, though, is the idea that we are not ourselves—rather, we are only the sum of a bunch of individual flecks that happen to be humming along in the shape of a person. The self is dissolved when that is understood. It’s also a potent image, I think, for what microbes and their clouds imply.
Page 187 · Location 2955
The plant and its microbes are likely inseparable. They are a composite organism, a tightly fused collaboration. I thought of another famous collaboration, the one in which a photosynthetic bacteria came to live within an algae cell, forming the predecessor of the earliest plant.
Page 188 · Location 2958
In the 1990s, pioneering evolutionary biologist Lynn Margulis first popularized the concept of a “holobiont,” which she defined as a composite organism made of many organisms working in concert. It includes the microbiome, but also the macrobiome—the larger beings in which and upon which the microbiomes live. Cells with nuclei include all mitochondria and chloroplasts, fundamental to both animals and plants. Margulis hypothesized that they first came into being when microbes of different abilities teamed up, eventually fusing into one entity.
Chapter 9: The Social Life of Plants
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eusocial behavior must have evolved separately many times. Clearly it is an evolutionary strategy for success, or it wouldn’t have spontaneously reappeared and persisted across distinct branches of life.
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if something works well, biology tends to reproduce it across the spectrum of life. A good idea has a habit of showing up again and again.
Page 197 · Location 3099
Light changes color when it passes through a plant, and the light that passes through different plants is altered each in a different way, far too subtle for us to notice but clearly distinct enough for plants to notice. Plants take note of the quality of light falling on them, and whether that light has passed through a plant before reaching them, which indicates a taller neighbor. They then grow their stems to certain lengths accordingly—taller when there are lots of neighbors around, and shorter when there are not. It makes perfect adaptive sense. If you’re at risk of getting crowded out, you grow taller to keep your patch of sun. “Phytocrome-mediated stem extension” is the official term for this behavior.
Page 198 · Location 3115
When surrounded by unrelated plants, searocket would grow roots prolifically, aggressively expanding into the sandy soil in an attempt to monopolize nearby nutrients. But when they grew beside their kin, they would politely confine their roots, leaving siblings space to make a living beside them.
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Looking at behavior is a different thing from looking at benefits to the plant.
Page 199 · Location 3127
populations of impatiens, a common garden flower native to Rhode Island. The plants seemed to be recognizing their kin too, and treating them better than strangers. The preferential treatment appeared in its aboveground behavior. When impatiens grew with strangers, they would frondesce as aggressively as possible, unfurling extravagantly to coopt as much of the sunlit space as they could. When planted beside kin, they would kindly arrange their leaves to avoid shading their siblings.
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Plants clearly can recognize their kin. But how they do this—through which sensory channels—is an ongoing line of inquiry, in part because the means appear to be various.
Page 201 · Location 3165
plants have a social life. They are aware of who they are in the company of, and decide how to behave toward them accordingly. Their suite of social dynamics goes well beyond kin recognition, too; carnivorous plants, for example, were recently discovered to have evolved to hunt in packs. Collaborating on catching insects allows them to lure larger prey.
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If culture is the idiosyncratic way that beings in a group conduct their business with each other,
Bookmark - Page 202 · Location 3184
Page 202 · Location 3185
rice planted with distantly related cultivars was so busy with aggressive root-building belowground
Page 202 · Location 3186
Much like how sunflower yields went up when relatives were planted together, cultures of closely related rice had more energy available to focus on rice making. Ultimately the team found that rice yield went up when rice was planted in mixed cultures of closely related cultivars.
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A field without altruistic plants is a field at war.
Page 204 · Location 3218
If a farmer were to instead select altruistic plants early in the breeding process,
Page 205 · Location 3226
to a plant, spatial awareness is everything. It samples the chemicals dissolved in the soil moisture, noting the flavor of its new neighbors. Some of them, the seed notes, are its siblings; seeds that have fallen off the same mother plant. Others are of a completely different species. This plant is still a mere embryo, but it already has a decision to make.
Page 206 · Location 3243
rhizosphere, the world of soil and the multitudinous organisms that live below its surface, in and among plants’ roots.
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There are as many as one billion microbes in a teaspoon of soil. Fungi weave their networks of hair-fine threads through nearly every square inch of ground. And plant roots, swerving and diving in search of food, interact with it all, and with each other.
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half a plant’s life is lived in the rhizosphere.
Page 206 · Location 3253
Fungal threads are hooked into the roots of nearly every plant grown in the wild, and may be crucial to the way plants communicate with one another belowground.
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Where a plant ends and a fungi begins becomes hard to parse. In fact it seems hardly a stretch to ask whether a plant is itself without fungi.
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“What we call ‘plants’ are in fact fungi that have evolved to farm algae, and algae that have evolved to farm fungi,” Sheldrake argues. By the time the first plant roots appeared, the plants had already been associating with fungi for fifty million years.
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Fungi, existing in the dark underground, can’t photosynthesize. So they get their supply of life-sustaining carbon from their plant associates, who spend all day making carbon-rich sugars and fats out of sunlight and air. In exchange, fungi supply plants with soil minerals like phosphorus, copper, and zinc that they mine from rock and decomposing material, which plants need but can’t always get on their own.
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Each root tip acts as both a gatherer and a sensor, integrating information about the rhizosphere into the whole root system, causing the architecture of the plant’s root network to morph and shift shape, like a murmur of starlings or a school of minnows.
Page 211 · Location 3324
Sunflowers are known allelopathics, meaning that they will secrete chemicals into the soil when resources are low to stop the germination of seedlings of other plants. As such, sunflowers are often good guards against invading weeds in garden patches.
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Plant cultures are multifactorial, like human cultures.
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Complexity—the marriage of the extreme idiosyncrasy of species and the constant fluctuations of a zillion variables in their environment—
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I think that we hurt ourselves in ecology, not just plants, but in community ecology in general, by relying a lot on super simplified models that were great at the start in the fifties and sixties, when they were put forward to help frame thinking of a new discipline. But people still use them and think that they are likely representative of what’s going on in reality.”
Chapter 10: Inheritance
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Unless you live on a small island or inside a ginkgo grove, the majority of plants you encounter are bisexual, meaning they have male and female parts, and are capable of producing the plant equivalent of both eggs and sperm.
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Wild radishes that have lived through a scourge of destructive caterpillars will make baby radishes with extra-bristly leaves too, plus they’ll be preloaded with defensive chemicals to better ward off threats. If these plant-children end up facing the same challenges their parents did, they’ll be much better prepared to handle them.
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Genes are the current stand-in for the code to life. Genes are of course important to many things in a plant’s life. But increasingly it seems like they’re less akin to a code that the organism reads out than to a flexible repertoire, a choose-your-adventure novel with a multiplicity of endings, each influenced by a million subtle changes in the storyline.
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Plants have a wide range of flexibility to transform into what their surroundings demand of them.
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plants—and every other living thing—have agency over their own development. They take into account their conditions, and then shape their own structure and function accordingly. At a deep, biological level, of course.
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The observation that a plant will develop very differently in one environment versus another is unavoidable to anyone who studies plants. “It tormented the scientists of the twentieth century,” she says. If they paid too much attention to it, it would surely ruin the results of uncountable experiments. Any variation was instead considered a quirk of a specific individual, an outlier in the data. There were a lot of outliers. But the idea that plants might be governed by more than just their genes would puncture the sheen of accomplishment forged by the genetic discoveries of midcentury. Scientists had found the basis for life. In the all-or-nothing thinking to which Western science tends to be devoted, the new genetic paradigm was absorbed wholly, and left no room for this kind of ambiguity. So it was mostly ignored.
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Genes were the puzzle pieces that made every living thing, and if we could find what each piece did, we’d know everything about organisms. They would become fully predictable. This belief extended far beyond plants, of course. Human genetics took on a godlike omnipotence. The gene for intelligence, the gene for homosexuality, genes for diseases and psychological conditions, they were all waiting to be found.
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“The DNA sequence . . . spells out the exact instructions required to create a particular organism with its own unique traits,” reads a paragraph on a U. S. government website about the human genome. To Sultan, that sums up the problem. Genes are not exact instructions. They’re more like stage cues at an improv show. A lot of other things could happen along the way.
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cruciferous vegetables like broccoli produce compounds that, when broken down in our bodies, turn into the enzymes that detoxify cancer-causing chemicals.
Page 230 · Location 3620
each living being, be it a plant or a fish or a human, is fully infiltrated by legions of microbes. These microbes often have yet-smaller microbes living inside them. Each of them is subject to environmental changes, too. Were they not a sort of community in themselves, and the body they lived in an ecosystem? It makes sense then, when we scale up to imagine a whole individual plant, or person, to not lose sight of its fundamental architecture, which is truly that of a community of creatures responding to changes in their world. Everything, at every level of life from a microbe to a rain forest, then, is an ecosystem. We are more like a system than a single unit. All biology is ecology.
Page 231 · Location 3629
plasticity likely varies dramatically between species; sometimes it will depend on where they evolved. Some, like the many “naive” native plants of Hawai‘i, have very little capacity to adapt to change, having evolved in a place without natural predators, and are handily outwitted by invasives. They just aren’t that plastic.
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Polygonum cespitosum has managed to evolve very rapidly to suit their new environment. They’ve become capable of colonizing all sorts of habitats in their new North American home. They have developed rapid lifecycles, during which they are wildly successful at reproducing. The ones who are best at this will no doubt become the future of their species, fueling generations that are themselves faster and more successful at reproducing. The result? Smartweed is rapidly evolving toward greater and greater invasiveness.
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invasive, defined most often as a non-native plant that spreads quickly and has the potential to cause harm, either ecological or economic.
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inherited plasticity,
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Invasive species have often been maligned as more aggressive, ruthlessly competitive. These are strangely moralizing concepts to put on a plant, when you think about it. The words we use for invasive species are very often unsubtle in their xenophobia, matching nativist language. We call them “aliens” and drape tropes on them about being unnatural in their abilities, aggressive by nature, like diseases on the land. But what if they’re just more resourceful, more plastic, better at handling change and passing on wisdom to their young? They certainly disturb our landscapes, and supplant species that we have grown to love, in our short evolutionary stint on the planet so far.
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This era is unique in that we are the ones moving plants around the world. We’ve caused—and are still causing!—most of these invasive species to show up in new places, to adapt to new scenarios and locations. We literally bring them there. It’s even stranger to fault a plant for its successes with this fact in mind.
Page 234 · Location 3688
Japanese knotweed, for example. There may be no plant more successful on the planet, or more hated. It is a close relative of the smartweed Sultan studies. Japanese knotweed was first introduced to North America in the 1860s by plant collectors seeking to add an attractive exotic species to their private nurseries. It had already been imported to Europe several years before. The plant became popular for its white flowers and dense coverage; it grew preposterously fast and thick as a hedge, perfect for privacy along roadsides. Apparently some people in the United States still intentionally plant it in their gardens. They clearly have no idea what they’re about to face. Once you meet a knotweed, the fact that plants can morph their bodies at will becomes searingly obvious. Their agency is almost palpable. Any illusion of human control falls away.
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knotweed grows rhizomatically, with continuously growing underground stems called rhizomes. Once established, it spreads a complex network of rhizomes beneath the soil, a subway system of runners and shoots, a continuous network with no clear center. It’s almost impossible to dig out and remove these vast rhizome networks, and without doing that, the plant can never be extricated. A fingernail-sized root fragment left behind can regenerate the entire plant. And knotweed-blanketed areas the size of half a football field have been found to be a single individual, one gigantic rhizome monster.
Page 237 · Location 3729
Already in the UK, the mere presence of Japanese knotweed on a property makes it unmortgageable.
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Japanese knotweed is now one of the most invasive plants in the world—or one of the most successful, from the plant’s perspective.
Page 237 · Location 3739
Its future is secure, thanks to its incredible plasticity, the agency it exudes through every new growing tip. We brought it here. It’s just doing a great job at being a plant where we put it.
Page 238 · Location 3747
The idea that plants have agency is bubbling up through the literature now, with Sultan at the helm (Simon Gilroy and Tony Trewavas are up there too). Agency is an emotionally loaded word. Sultan is taking a gamble by using it. It immediately calls to mind the existence of a mind, of intention and desire. But she says we need to get past that. “It’s not intentional, and it’s not intelligent in the way most people use that word. But it is agency,” she says, clearly trying to distance herself as much as possible from anyone trying to portray plants as little humans. Agency is an organism’s capacity to assess the conditions it finds itself in, and change itself to suit them. Yes, we do this all the time. So do plants.
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Mechanistic visions of being controlled only by our preprogrammed genes do not satisfy our innate understanding of ourselves as brimming with irreducible complexity and subtlety. We too are like plants, taking in information from outside our skin, the membrane separating us only barely from the world we live in. Beneath the surface of every organism there is a vibrancy we do not know, yet, how to completely dissect or replicate. Complexity is mounting instead of receding.
Chapter 11: Plant Futures
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From the viewpoint of the evolutionary biologist it is reasonable to assume that the sensitive, embodied actions of plants and bacteria are part of the same continuum of perception and action that culminates in our most revered mental attributes. “Mind” may be the result of interacting cells. Mind and body, perceiving and living, are equally self-referring, self-reflexive processes already present in the earliest bacteria.—LYNN MARGULIS AND DORION SAGAN, WHAT IS LIFE?, 1995
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my lingering question of how we should think about them.
Page 241 · Location 3788
Humanity has proven its failure as an evolutionary project and chosen a path of generalized destruction.
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General System Theory, a slim book by Ludwig von Bertalanffy, which outlined the idea that biology was in fact an agglomeration of systems or networks, which were all interconnected.
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This was the dawn of network theory. The properties of organisms and populations emerged from these connections, von Bertalanffy wrote—from many parts interacting as a sort of whole. A plant is an emergent system like that, Trewavas decided back then. They’re networks.
Page 244 · Location 3824
It is hard to underestimate the drama of being a tree, or any plant. Every one is an unimaginable feat of luck and ingenuity. Once you know that, you can’t unknow it. A new moral pocket has opened in your mind.
Page 245 · Location 3849
the small miracle of its germination, the craning of its elongation, the articulation of the hundreds, maybe thousands of fine root hairs, right now probing its belowground world for sustenance. I think about the stem cells in each of its growing tips, poised and ready to become whatever sort of flesh the plant needs them to be. The whole being a sensitive, decisioning network spread throughout hundreds of limbs, thousands of roots. A body in motion, adapting in real time to every subtle shift, flowing like water through its surroundings and taking note of the shape and smell and texture of it all.
Page 247 · Location 3879
We now know that plants do speak, in chemicals. Their health status, their assessment of risk in real time, and even the quality of their nectar is decipherable to us now by sampling the volatile chemicals they exude. They communicate with one another, and with members of other species when the situation calls for it. At what point do we decide that plant communication qualifies as language? What would it do to our own minds if we decide it does?
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As soon as we reorient away from human modes of expression, we open ourselves to other worlds of being. We’re learning more every year. Language may already be there, for a plant. We may not yet know how to hear it.
About the Publisher
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The question of human consciousness is mostly an ongoing debate between two camps. The first are those who believe we owe our consciousness to a force beyond the material workings of our brain—something like a soul, let’s say, or an as-yet-undiscovered property beyond or apart from our physical brain matter. Panpsychists fall under this camp. The second broad camp are those who think consciousness is purely a biological phenomena borne of evolution just like everything else in nature, and that its cause is most likely located in the immeasurable complexity of the organ in our skulls; we just haven’t discovered the mechanism yet. This camp are sometimes called the materialists. But neither broad theory technically requires a brain, at least not in exactly the way ours happens to exist. In fact, both could leave room for the possibility of consciousness in degrees, rather than something a creature has or does not have. If consciousness is the result of a transcendent, free-floating property of the universe, could a creature not have more or less of it than its neighbor? And if consciousness is simply an emergent property of biological evolution, couldn’t that trait simply have been more or less emphasized in the evolutionary trajectory of each creature? When it comes to plants, the question at hand is whether consciousness could appear in something other than ourselves and a select few animals at all.