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1 Do Plants Have Minds?
1. Blithe Confidence
I was certain that plants didnât have minds. So certain, in fact, that I never even considered it. Although they are alive, although they grow, plants just sit there. That doesnât require a mind, or intelligence. On the contrary, such idleness suggests the absence of a mind or intelligence. People use âvegetableâ as a synonym for âmind-less.â When you veg out, you stop thinking. A person in a persistent vegetative state has âcomplete unawareness of the self and the environment,â and shows âno evidence of ⌠responses to ⌠stimuli.â1
Then I learned that some smart, informed people earnestly believe that plants have minds. Writing more than ten years ago in Nature, Anthony Trewavas, a fellow of the Royal Society of Edinburgh, plant physiologist, and molecular biologist, said that âthe investigation of plant intelligence is becoming a serious scientific endeavor.â2 He was right. There is now a professional society and journal dedicated to exploring the topic.3
Watching a time-lapse film of root growth with my six-year-old son, I started to appreciate their point of view. We were astonished at how much the roots looked like worms searching for food. They grow downward, until impededâperhaps by a pebbleâand then they turn, heading downward again after a short distance. If they touch the impediment again, or encounter a new one, they turn again (Figure 1.1). Similarly, although I knew that plants get energy from the sun, in time-lapse video many plants can be seen turning towards the sun; some track the sunâs position across the day. On an average âleafyâ tree, you will see that the leaves generally donât overlap, seeming to optimize the amount of leaf surface that is exposed to the sun, thus optimizing access to food.4
Plants are impressive in many ways. Bristlecone pines are some of the oldest living things. Methuselah in the White Mountains of California is estimated to be 4,800 years old. Many plants are âclonal,â producing seemingly distinct, but genetically identical individual stems or trunks. Pando, a quaking aspen in Fishlake National Forest in Utah, covers roughly 100 acres, with about 40,000 trunks, and roots estimated to be a shocking 80,000 years old. Banyan trees have adventitious roots that descend from their branches, looking like extra trunks, covering tremendous space. Thimmamma Marrimanu in Andhra Pradesh, India, has a canopy of roughly 4.5 acres, about two city blocks. These numbers are impressive in part because these things are alive.
Figure 1.1 Roots and shoots growing
Why was I so sure that plants didnât have minds? It depended, I knew, on what I thought about plants and minds. What can plants do? What is a mind? I didnât know much about plants, but I was so confident that they didnât have minds that I even doubted that learning more about them could convince me otherwise. Thus, I realized that much of my confidence stemmed from what I assumed about minds. From my education and research in philosophy, I knew a lot about theories of minds. When I started to reflect on what those theories imply about plants, I expected to be vindicated. I expected to find that the idea of plant minds is very old and was eventually cut down, killed, by more modern theories, even if it wasnât immediately obvious to me which theory struck the lethal blow. To my surprise, that is not what I found. The idea of plant minds is indeed very old, but it was never killed. Modern theories of minds have actually nourished itâincluding the theory that currently dominates cognitive science and (broadly Western) philosophizing about the mind.
Uncovering my excessive confidence about plant minds felt, strangely, very good, like noticing for the first time a handsome tree on a path youâve traversed for years. It gave me something new and interesting to contemplate: Do plants have minds?
Itâs worth considering. Whether or not youâre open to the possibility that plants have minds, youâre probably relying on questionable assumptions about plants, minds, and ourselves, and about life too. Having those assumptions exposed and interrogated can be, I have found, energizing, like breathing fresh air after driving through a recently fertilized cornfield.
In this book, relying on current consensus ideas about minds, I present the best case for thinking that plants do not have minds. Along the way, I unearth an idea at the root of that case, the idea that having a mind requires the capacity to represent the world. In the end, I defend a relatively new and insightful theory of mind that rejects that assumption, making room for the possibility that plants do have minds, primarily because they are alive. Throughout, I assume that you, my reader, do not have special knowledge of plants or minds. Thus, I aim to introduce the big ideas to you, making suggestions for further exploration in my footnotes.
In this first chapter, we see that it has been very difficult to figure out what a mind is. Yet doing so is essential for determining whether plants have minds. To help you get started thinking more carefully about whether they do, I will introduce a selection of the most interesting and influential ideas in the history of thinking about minds, ones that will be helpful as we dig deeper. Reflecting on these ideas will also help reveal how I was wrong simply to assume that plants donât have minds.
2. Goal-Directed Order
A truly ancient and compelling idea is that a mind displays a distinctive type of order, order directed at a goal.
Panpsychism is the idea that all thingsânot just persons or plants, but also puddles, rocks, planets, hair, fire, worms, birdsâhave a mind or a mental aspect. It may seem outlandish, but some intelligent ancient Greeks found it compelling.5 When I pause over that fact, one big idea stands out. Nearly everything is orderly.6 There are patterns or regularities in things. Drop a rock in a puddle; ripples radiate concentrically. Wait a moment; do it again; the same thing happens. Rocks flake and crack in predictable ways when struck. Each day, the sun moves across the sky in the same direction, altering its trajectory incrementally throughout the year. More complicated is the moonâs position, its waxing and waning, but there are discernible patterns there too. Plants start small and get bigger; most grow flowers and fruits, then shed them. Although less predictable in various ways, animals, too, are orderly. Dogs chase cats, who chase rats. Flies are drawn to meat and fruit. Like us, the ancient Greeks marveled at the universe, partly because it displays tremendous order.
Now, such order need not imply that each thing has a mind, or that the universe as a whole has a mind, or is made or guided by a mind, but it is tempting to draw that conclusion. The extent and degree of order can seem like they must be produced by intelligence. It is especially tempting to think this in the absence of any plausible alternative.
Aristotle (384â322 B.C.E.) was not a panpsychist, but thought instead that every living thing had psuche (pronounced soo-kay), which is commonly translated as âsoul,â and which is the ancient origin of our root word âpsych-,â as in âpsycheâ and âpsychology.â7 He was an astute observer of organisms; Ernst Mayr, one of the most influential biologists of the twentieth century, thought Aristotle was the most important contributor to biology before Charles Darwin.8
That might make it seem as if Aristotle thought every living thing has a mind, but that is not exactly right. What he meant by âpsucheâ is not what we often mean by âmind.â For Aristotle, âpsucheâ names the sort of order characteristic of a living thing; it is the way a living thing is directed at a distinctive goal, such as nutrition, or detection of its environment, or understanding of its place in the universe. We, by contrast, use âmindâ for a thingâs ability to think and remember. So, we should not hastily equate psuche and mind.
Aristotle thought there were three types of psuche, the highest of which was intellect (what he called ânousâ). The two lower types were nutrition and perception. For him, plants engage in nutrition, the lowest sort of soul, but not the other two; nonhuman animals engage in nutrition and perception, but not intellection; and humans engage in all three. Having a particular type of psuche is to strive toward particular goals, which structure oneâs activities. Plants grow and seek nourishment, and should be understood and evaluated in terms of whether and how they do so. For instance, an olive tree might not get enough water, and therefore fail to reach its goal of nourishing itself. Nonhuman animals, in addition to seeking nourishment, also perceive their environment, and should be understood and assessed accordingly. For instance, a dog might notice a crevice in its path as it chases a squirrel, turning accordingly. Humans have all three types of psuche, and are distinguished from other organisms by having a rational or intellectual soul, which allows them to deliberate about what to believe (will it rain?) and about what to do (should I visit my friend?).
Thus, in Aristotle, we find the idea that to have âpsucheâ is to display a distinctive type of orderliness: orderliness directed toward a goal. Although only humans have the most sophisticated form of it, intellect or reason (ânousâ), all organisms display it; all organisms have âpsuche.â
Thus, Aristotle gives us two important ideas about the mind. It is a type of goal-di...
