Part 3 (1/2)
I had been looking into intelligence in nature for eighteen months when a friend called to draw my attention to a recent article in the journal Nature. It claimed that the investigation of plant intelligence is ”becoming a serious scientific endeavor” and that scientists are ”only now beginning to expose the remarkable complexity of plant behavior.” These were the words of Anthony Trewavas, a professor of biology at the University of Edinburgh and a fellow of the Royal Society, the oldest scientific society in Great Britain. According to Trewavas, plants have intentions, make decisions, and compute complex aspects of their environment.
I looked into the research cited by Trewavas and found, to my surprise, that scientists were now saying that plants have senses and can detect a wide variety of external variables, such as light, water, temperature, chemicals, vibrations, gravity, and sounds. They can also react to these factors by changing the way they grow. Plants can forage and compete with one another for resources. When attacked by herbivores, some plants signal for help, releasing chemicals that attract their a.s.sailants” predators. Plants can detect distress signals let off by other plant species and take preventive measures. They can a.s.similate information and respond on the whole-plant level. And they use cell-to-cell communication based on molecular and electrical signals, some of which are remarkably similar to those used by our own neurons. When a plant is damaged, its cells send one another electrical signals just like our own pain messages.
A good part of this knowledge emerged during the 1990s thanks to the development of molecular genetics, which revealed the signals and receptors used by plant cells when they communicate and learn. Anthony Trewavas helped launch this field of investigation with his research on calcium and plant signaling. I contacted him and requested an interview, explaining my purpose. He accepted, and we set up a date.
I arrived in Edinburgh on a cold, stormy January night. As I walked along the streets, I braced myself against the wind and rain. It was my first trip to Scotland. It felt bleak, and I wondered whether I had come to the right place to find out about plant intelligence. I stayed in a hotel on the outskirts of town.
The next morning, the rain had stopped. I made my way over to the university and arrived well ahead of our planned meeting. I wandered around the corridors of the Inst.i.tute of Cell and Molecular Biology, a nothing-special building designed in the 1960s, which now seemed run-down. Corridors in science departments tend to look alike from one country to the next, with drab walls covered with posters announcing conferences or explaining research.
I found Anthony Trewavas in his office on the fourth floor. A tall, balding man, he has piercing light-blue eyes and gray eyebrows. He invited me in and showed me a chair where I could sit down. His office was littered with stacks of journals such as Science and Nature. I glanced at the top file on the nearest pile of doc.u.ments and saw that it was ent.i.tled ”Intelligence.”
By the time I turned on the tape recorder, Trewavas was already discussing the importance of plant intelligence, saying that scientists have long regarded plants as pa.s.sive creatures, because they lack obvious movement. ”Now to my mind, that a.s.sumption is wrong because it requires an equating of movement with intelligence. Movement is an expression of intelligence. It is not intelligence itself. Now, the definitions of intelligence are difficult””
He spoke fluidly, needing no prompting to continue his line of thought. He said he found it necessary to peel away the human aspects that come with the notion of intelligence. In his view, our intelligence did not suddenly appear when we became h.o.m.o sapiens. It evolved from other organisms. Hence the importance of defining intelligence in a way that does not apply exclusively to humans. Trewavas referred to the definition devised in 1974 by New Zealand philosopher and psychologist David Stenhouse, who described intelligence as ”adaptively variable behavior within the lifetime of the individual.” This can apply to many different organisms and means noninstinctive behavior that maximizes the individual”s fitness.
Trewavas”s desk stood against a bay window overlooking Edinburgh. He sat facing me, with his back to his desk. He looked straight at me as he spoke. His eyes had a piercing quality, but his tone was generous. He said he had spent years pondering the behavior of plants in the light of Stenhouse”s definition. Though most plants do not move at a speed perceptible to the naked eye, they respond as individuals to signals from their environment and develop in adaptively variable ways. Even plants growing in pots inside houses turn their leaves to the light to optimize light collection and send their roots down in the soil and their shoots up into the air. And wild plants manage to compete with other plants for resources. Research now shows that growing shoots can sense neighboring plants. They can detect s.h.i.+fts in infrared light indicative of nearby greenery, predict the consequences of that presence, and take evasive action. Plants can alter the shape and direction of their stems to maintain an optimal position relative to sunlight. They can adjust their growth and development to maximize their fitness in a variable environment. According to Trewavas, this means they are intelligent, if one refers to Stenhouse”s definition.
To ill.u.s.trate his point, Trewavas described the behavior of the stilt palm. This tropical tree has a stem raised on prop roots and moves toward sunlight by growing new prop roots on the sunny side and letting those in the shade die off. By doing this over several months, the stilt palm actually changes places. It ”walks” around in this manner, fending off compet.i.tive neighbors and foraging for light, at a speed imperceptible to humans. Trewavas considers this a clear example of ”intentional behavior.”
Ground ivy is another plant with measurable foraging skills. This perennial weed creeps along the ground as a vine, and when it reaches a patch of optimal size and nutrient content, it puts down roots and generates leaves to catch the light. Scientists recently tested ground ivy in a controlled environment in which nutrients were distributed unevenly. The plant demonstrated that it senses resources by starting to grow roots much earlier in its development in the locations containing nutrients and by skipping over the poorer ground between rich patches. Trewavas finds it ”difficult to avoid the conclusion of intention and intelligent choice” in the case of ground ivy.
Such examples cannot be dismissed as preprogrammed rote responses, he said. Rather, they demonstrate plasticity. He explained that an individual plant has an enormous capacity for changing its morphology, its branching structures, to accommodate the environment in which it finds itself. The transformation occurs very slowly from a human point of view, over a period of months, rather than milliseconds. ”But the way in which it is conducted and the success with which it has occurred must indicate that a lot of computation goes into the decisions which are actually made, otherwise plants would not dominate this planet in the way that they actually do.”
Trewavas had obviously argued in favor of plant intelligence many times. I was willing to consider that Western cultures, and science in particular, had misjudged the vegetal world. But I wondered about the extent of plants” capacities. I asked Trewavas if he thought plants think when they make decisions. He replied that he did not. In his opinion, they compute what is actually going on, then make appropriate responses in terms of what they perceive.
Having answered my question, he continued making the case for plant plasticity. Plants have to gather resources in their local environment while facing compet.i.tion from their neighbors. As they are mainly fixed in one place, the most sensible way any plant can do this is to occupy the s.p.a.ce around itself in an optimal way. A branching structure happens to be the simplest way in which this can be done, and this is the solution plants adopt, both below ground, as they send down roots into the soil to form exploitative tissues, and above ground, as they deploy their leaves to gather the maximum amount of light. To do all this, an individual plant must perceive a gravity vector and align itself correctly. And its actual shape and morphology are determined by the quant.i.ty and quality of light it perceives. For Trewavas, this is ”adaptively variable behavior within the lifetime of the individual, i.e., intelligence.” Furthermore, individual plants do not choose their environment, as seeds land and germinate where they can. Plants have to grow in a great variety of environments and adjust their structures to optimize their ability to exploit what they find.
Trewavas”s favorite example of vegetal intelligence and plasticity is a parasitic plant called dodder. It moves around by wrapping itself around other plants and correctly estimating their nutritional quality. Within an hour, dodder decides whether to exploit a host or to move on. If it stays, it takes several days before beginning to benefit from its host”s nutrients. But dodder antic.i.p.ates how fruitful its host will be by growing more or less coils. Growing more coils allows greater exploitation; but if the host is poor in nutrients, this wastes precious energy, because dodder lacks leaves and relies on its hosts for water and food. So it has to make correct decisions or face death. Botanist Colleen Kelly, working in the early 1990s, found that dodder correctly a.s.sesses when to eat and when to move on, and that its foraging strategies have the same efficacy as those of animal foragers. And it computes the right choice between close alternatives without the benefit of a brain.
Trewavas described plants as having intention. But I had in mind Jacques Monod”s statement that attributing purpose or goals to nature contradicts the central method of science. According to Monod, studying nature scientifically means ignoring the possibility of intention. I reminded Trewavas of this postulate and added that he seemed to have crossed the line.
He scoffed: ”Well, I don”t know how many people actually believe Jacques Monod in that regard. That was an idea that did not really apply to humans, did it? It seemed to devitalize life in my own view. It seemed to indicate that life was solely governed by chance. And animals have foresight. And so do we. And to me, plasticity must be foresight, because it”s the ability to adjust to the particular environmental conditions which you find. If you didn”t have that ability, then you would not be able to accommodate optimally to that. Possessing plasticity is in a sense foresight of the possible conditions in which the plant will actually find itself.”
How, then, does a plant make up its mind? I asked. Trewavas replied that he had pondered this question for many years. In 1990, he and his colleagues had a breakthrough. They were studying how plants perceive signals and transmit information internally. Using genetic manipulation, the scientists inserted into tobacco plants a protein that makes them glow when calcium levels rise inside their cells. They suspected changes in cellular calcium concentration to be a major means by which plants perceive external events. To their amazement, they found the tobacco plants responded immediately to touch. Though tobacco is not known to be touch-sensitive, one gentle stroke caused the modified plants to glow with the light produced by the elevation of calcium inside their cells. Trewavas was dazzled by the speed of the response: ”It was as fast as we could measure. Whereas I have been telling you that plants only respond in terms of weeks and months, in this case, they were responding in milliseconds to a signal which we knew would later have a morphological effect. If you keep touching a plant, it slows down its growth and it gets thicker.”
Trewavas knew that human neurons also use internal calcium elevation when they relay information. Once he saw the speed of the plants” reaction to touch, he started thinking about intelligence. Plants may not have neurons, but their cells use a similar signaling system, he told himself, so they may have the capacity to compute and make decisions.
As I listened to him, I realized that he had firsthand experience of the changes that had swept across contemporary biology in recent decades. He had opened himself to the idea of intelligence in nature. This was a courageous step for a Western scientist. I knew indigenous people in the Amazon who consider it a matter of course that plants have intelligence. But in Western cultures, those who attribute intelligence to plants have long been the objects of ridicule. Until now, scientists, and in particular botanists, had avoided using the words plant intelligence. I wanted to know more about how his thinking had changed and pressed him for details.
Gesturing at the doc.u.ments piled around his office, he said he had read up on a number of different subjects over decades. He described his work method in some detail. ”The family used to complain that I would sit in a chair vacantly thinking. I found it very necessary to do. The ideas don”t just come by reading. You have to go away, lie down, sit down, walk about, and let things turn over in your mind. And what I find particularly enjoyable is a problem I”m trying to solve in my own mind. Is there something I can connect together? And I find it”s only by long periods of doing nothing but think that suddenly facts start coming into your mind. And they come together in an interesting combination which enables you to see the possibilities for what plants can actually do.” He said the notion of plant intelligence had come to him in this fas.h.i.+on. Intelligence in general was a subject that had interested him for years. So when he saw the connection between plants and calcium, it inevitably led him to think about intelligence.
Trewavas”s intuition about calcium”s role in learning in both animals and plants was confirmed by subsequent research. Scientists recently discovered that when an animal learns to avoid a threat, charged atoms of calcium and specific molecules including enzymes are unleashed inside its neurons. They set about modifying the molecular structure of the channels that span the neurons” outer membranes and control the import and export of charged atoms and molecules. If the threat to the animal persists, its neurons go on to produce proteins that build new connections, or synapses, between neurons. Along with changes in the strength of existing connections, these new synapses give rise to memory, and allow the animal to remember the threat and avoid it.
An a.n.a.logous process occurs in plants. When a plant is threatened, by lack of water, for example, exactly the same atoms and molecules are unleashed inside its cells. And they set off the same reactions, first modifying the same import-export channels, then stimulating the production of proteins if the threat persists. Eventually, the plant modifies its cells and their behavior so that its leaves get smaller, its shoots cease to grow, and its roots extend. These responses minimize further stress and injury to the plant. They also take into account external factors such as nutrients and temperature, as well as the plant”s age and previous history.
Science now indicates that plants, like animals and humans, can learn about the world around them and use cellular mechanisms similar to those we rely on. Plants learn, remember, and decide, without brains.
WE HAD BEEN TALKING for an hour and a half. Trewavas invited me to accompany him to the rooftop cafeteria for a cup of coffee. We wove our way through a labyrinth of corridors and staircases, and through packs of students coming in and out of lectures. The cafeteria was quiet and luminous. It offered a spectacular view of Edinburgh and its surrounding hillsides on a crisp winter day. Trewavas was being generous with his time and knowledge, and was certainly one of the easiest people to interview I had ever met. There had been moments during our conversation when I found it difficult to get a word in edgewise.
Drinking coffee together seemed to be a good time to get more personal. I decided to ask him whether his own behavior toward other species had changed in light of his scientific research. After all, his work showed that we have more in common with plants than most people suspect. He replied that his behavior had not changed much, as he had always respected other species, and had always enjoyed the company of plants and animals. This led him to discuss cruelty toward animals, a much-debated subject in Great Britain. Upon reflection, he realized that his behavior had changed on one count, namely that he had given up fis.h.i.+ng. He had come to feel sympathy for the fish, because he could see that a fish on the line is frightened out of its life. Now he considers fis.h.i.+ng to be relatively cruel. From his point of view, it is self-evident that animals feel pain. ”You throw a fish out of water, and it”s flapping around; well, the reason it”s flapping is because it”s trying to get air. And I suppose I can anthropomorphize that situation and see that I would be doing exactly the same d.a.m.n thing if I was put into water, trying to get air in my lungs, not water. But I like eating fish. I just prefer someone else to catch it. We have to respect the system in which we live, because it will not survive if we don”t respect it. And that”s all there is to it, and I think that is vaguely self-evident. On the other hand, you can”t go overboard about it. We are the important organisms. It”s us discussing the environment and other animals, and not the other way around.”
”To our knowledge,” I interjected”meaning that we could not be sure that other species were not discussing us. But this did not stop his train of thought. He said that we had to learn to live with other species, and he referred to the work of a fellow member of the Royal Society who had carried out hormonal studies on deer that had been hunted; it showed beyond doubt that these animals were extremely frightened. Trewavas now views hunting animals for pleasure as a lack of respect for life. It was simply untrue, he said, that foxes enjoy a good hunt before being torn to pieces. I found nothing to argue with there.
We returned to his office to wrap up the interview. I asked him about future research on plant intelligence. What remained to be done, he said, was to work out how the whole plant a.s.sesses its circ.u.mstances, makes a decision, and changes what it is doing in response to the environment it perceives. ”That requires a lot of communication between the various parts of a plant. It has become an extremely complex area, remarkably complicated. And I can see that we have underestimated this in the past to an enormous extent. People are going to have to keep working on this and try to appreciate that what they are looking at, in fact, is an organism that does exhibit intelligent behavior, and not in ways they normally perceive intelligence.”
It was still not clear to me how and where computation occurs in a plant. According to a view Trewavas had expressed in writing, ”plant communication is likely to be as complex as within a brain.” I told him that when I read that sentence, I pictured the whole plant as a kind of brain.
”Yes, that”s interesting,” he said. Then he began comparing the chemical signals used by neurons to those used by plants cells. Some are the same, but others are different. Brain signals tend to be small molecules, whereas plant signals tend to be large and complicated, such as proteins and RNA transcripts. This had only become clear in the last five years, he said. Prior to that, ”no one would really believe that proteins would be swimming around a plant providing information.” And large molecules can handle large amounts of information, which means there is room for enormous complexity in plant communication. ”But you are quite right when you ask about computation: Where does it actually exist? I just don”t know. And the answer is almost certainly: It”s in the whole organism.”
Plants do not have brains, so much as act like them.
Later that day, I wandered through the streets of Edinburgh. The clouds had cleared, and the winter sun lay low on the horizon. The city and the volcanic cliffs overlooking it were bathed in pale light. I went over the morning”s conversation with Anthony Trewavas. We humans have different timescales from those in plants. Consequently, we do not see plants move and a.s.sume they are stupid. But this is an incorrect a.s.sumption caused by our animal nature. We do not see them move because we operate in seconds, rather than weeks and months.
I stopped on the sidewalk of the cobblestone street leading up to Edinburgh Castle and remained immobile. I breathed and watched people walk past. I tried s.h.i.+fting to a plant”s timescale, but my thoughts kept racing at animal speed. An image popped into mind of Trewavas sitting in an armchair, not moving, thinking about plants. He was acting like a plant to understand plants, and attributing intelligence to them. Like a shaman, he identified with nature in the name of knowledge. His eyes were s.h.i.+ning.
Chapter 8.
SMART SLIME.
Seeing that plants can make decisions led me to look into other cases of intelligent behavior by brainless organisms. I focused on simple species in search of the basic conditions of intelligence.
Amoebas attracted my attention. Their name comes from the Greek amoibe, meaning change. These microscopic single-celled creatures mainly consist of a blob of protoplasm surrounded by a porous, flexible membrane. Amoebas move around by transforming themselves. They change the shape of their bodies by s.h.i.+fting their jellylike contents and stretching their membranes to form extensions known as pseudopods, or ”false feet.” Amoebas are shape s.h.i.+fters, transformers.
Some amoebas have the capacity to merge with one another to form a single giant cell, with thousands or millions of nuclei. Known as true slime molds, these peculiar unicellular organisms can grow as big as a human hand. And if one of them is diced up, the pieces will put themselves back together. Creeping around slowly and engulfing food along the way, true slime molds act like giant amoebas. There are approximately one thousand species of true slime molds, and they occur around the world, in particular in temperate forests. In their visible, aggregate state, they look like glittering blobs of mucus, or spilled jelly. They can be white, red, orange, or yellow. Typically, a true slime mold changes shape as it crawls over damp wood, leaves, or soil, ingesting bacteria, molds, and fungi. Its entire body is covered by a layer of slime, which it secretes continually and leaves behind as it crawls forward. Though true slime molds are composed of only one large cell, and therefore lack nervous systems and eyes, they can move, navigate, and avoid obstacles. They can also sense food at a distance, and head unerringly toward it.
True slime molds defy categories. They move around to feed themselves, like animals. But they give rise to fruiting bodies containing spores, like fungi. Once their spores disperse to new habitats, they ”germinate” into microscopic amoebas. The true slime mold”s life cycle is completed when these tiny amoebas merge into a single, giant cell. True slime molds spend their lives going between two kingdoms, fungi and animal, and between two scales, microscopic and macroscopic.
Scientists recently discovered that true slime mold, Physarum polycephalum, can consistently solve a maze. They found that when separate pieces of this bloblike organism are placed in a maze, they spread out and form a single cell, which fills all the available s.p.a.ce. But when food is placed at the start and end points of the maze, the slime mold withdraws from the dead-end corridors and shrinks its body to a tube spanning the shortest path between food sources. The single-celled slime solves the maze in this way each time it is tested. ”This remarkable process of cellular computation implies that cellular materials can show a primitive intelligence,” the scientists concluded. The j.a.panese biologist who initiated the experiment, Tos.h.i.+yuki Nakagaki, declared: ”I must recognize that this organism is so clever and cunning.” A common view is that intelligence requires a brain. And brains are made of cells. But in this case, a single cell behaves as if it had a brain.
If a single cell of yellowy slime can solve a maze, does this not confirm that the entire edifice of life contains intelligence? I read other publications by Tos.h.i.+yuki Nakagaki with t.i.tles such as ”Amoeboid Organisms May Be More Clever Than We Had Thought” and conclusions such as ”I had better change my stupid opinion that a unicellular organism is stupid.” I liked what I read so much that I contacted Nakagaki and requested an interview. He replied positively, and I began planning a trip to j.a.pan, a country I had never visited, and where few people speak European languages. I invited along my companion, Beatrice, who has traveled widely in Asia and who is a speech therapist.
In late July, we caught an all-night flight from Switzerland to Tokyo, then flew north to Sapporo, where Nakagaki works as an a.s.sociate professor at Hokkaido University. We arrived in the middle of the afternoon local time, checked into a hotel, had some coffee, then walked around town. The weather was sunny and crisp. Sapporo is modern and easy to get around, with tree-lined avenues. It reminded me of Vancouver. We ended up in a j.a.panese-style Italian restaurant called Africa and drank too much wine.
The following morning, we overslept and barely managed to make our appointment in the hotel lobby. Fortunately, Nakagaki was running late. It was raining outside. He showed up perspiring and carrying an umbrella. He was wearing wire-rimmed gla.s.ses, which suited his oval face. His short black hair was slightly graying on the sides. He seemed to be in his early forties. He dressed in an elegant and relaxed style: a checked s.h.i.+rt, green pants, socks, and thongs. Western clothes, j.a.panese footwear.
We walked under umbrellas as he led us across the campus. There were tall trees and s.p.a.cious lawns between the buildings. Nakagaki explained that an American had founded the University of Hokkaido in the nineteenth century. At one point, he turned to me and said, ”Actually, you are not a scientist.” I was surprised by his directness. No one had said this to me before; in fact, people often a.s.sume the contrary. But I agreed with him.
We reached the Research Inst.i.tute for Electronic Science, where Nakagaki has his office and laboratory. On entering the building, he asked us to take off our shoes and put on slippers, following j.a.panese custom. As we walked up the stairs to the third floor, he gestured at the walls and said, ”This is a cheap building.”
Nakagaki”s office appeared bare. It contained a desk, three basic chairs, simple white shelves filled with books, and a writing board. There was a large computer on his desk with a screen showing an e-mail in j.a.panese script. It caught my attention, and I noticed that the keyboard was marked with European characters. I asked how one wrote in j.a.panese on such a computer. He explained that j.a.panese uses three different scripts, including an ideographic script of Chinese origin, an alphabet of syllables to make up for the differences between Chinese and j.a.panese grammars, and a second alphabet of syllables for representing words imported from European languages. He went to the writing board and started showing us the different scripts. Then he returned to the computer and showed how one could s.h.i.+ft the keyboard into a mode that allowed one to compose all three j.a.panese scripts. I felt relieved that Nakagaki spoke English.