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The Inner Life of Plants: Cognition, Sensibility, and Ethics

At the end of last year I published an interview with the editors of a fascinating book called The Mind of Plants: Narratives of Plant Intelligence. It was quite popular and generated a large number of emails with questions about plant intelligence, consciousness and sentience, as well as stories from people who had witnessed what they called learning, thinking and feeling in a wide variety of ” intelligent plants. An email I received from Brad asked, “Given what we know, should we be mindlessly mowing lawns and cutting down trees?” Madeline wanted to know, “What will it mean when we learn that plants are sentient beings? Is it okay to eat them?”

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Two weeks ago I read an essay called “Radical New Experiments Hinting at Plant Consciousness” by Natalie Lawrence which nicely sums up what we know in a growing field called “plant neurobiology” (how plants process information) and points out where more research is needed. needed as we learn about their intelligence, behavioral plasticity, personalities, and much more.

Here is a summary of some of the research covered by Ms. Lawrence.

  • Plants are susceptible to anesthesia; lidocaine applied to the roots works well to kill the plants.
  • Plants have a social life; they communicate with each other, react to what happens to them and around them, and interact with other species, including non-human animals (animals). For example, chemicals released by tomato plants encourage caterpillars to cannibalize each other.
  • Plants display cognition: flexible, goal-directed behavior. Climbing a pole, a smart bean makes “wide, circular sweeps of its surroundings, growing larger as it goes. As they approach a pole, a few beans suddenly lunge at it like a drunken pub-goer punching someone.” It is a rapid and directed change in behavior. This suggests that the plant is not simply executing a preprogrammed pole-finding sequence.” Researcher Paco Calvo, who works at the Minimum Intelligence Laboratory of the University of Murcia in Spain, suggests that this could show that the bean knows that the polo is there, but he cautions that we need more research.He and his colleagues have shown that the charging of beans is accompanied by spikes in electrical activity, suggesting a possible “level of sentience” of brainless plants.
  • Plants can be sentient. Calvo believes that the flexible behavior that plants display suggests that they may have “unique subjective experiences.” When the ways plants grow are combined with the fact that they have electrical signals, it is reasonable to postulate that they have some kind of consciousness, possibly explained by what is called integrated information theory. This theory considers consciousness as the ability to integrate different aspects of experience into a whole.
  • Plants can learn and remember. One study showed that plants can learn to grow toward the breeze, somewhat like the Pavlovian conditioning that dogs display. However, there is much debate about the robustness of these data due to failures in replication of the findings. (More information can be found here).
  • Plants have “personalities.” Based on “genetic wiring and behavioral flexibility,” individual violets can be labeled bold or cautious based on how long their leaves fold after being touched.
  • Domesticated plants tend to be “less cunning and independent” than their wild relatives. Lawrence writes, “Wild vines, for example, can scan their environment for something to climb on and quickly scale it. In contrast, domesticated vines stumble unless they have trellises or posts placed next to them. You could think of them as the pampered lapdogs of the plant world”. When houseplants go feral, they behave more like wild members of their species. (Domestic animals tend to be more docile than their wild relatives.)

Where to from here?

Needless to say, there is much healthy and much-needed discussion, debate, and skepticism about most, some would say all, aspects of plant cognition, sentience, consciousness, behavioral flexibility, personalities, and learning.1 Brad and Madeline’s emails about what it means for plants to be sentient and have feelings show that there are also important ethical issues to consider.

The amount of sustained interest in the internal life of plants by highly accredited scientists tells me “there’s something out there,” and I look forward to further study of the fascinating minds of a wide variety of flora. It would not be surprising if we learn that there are differences between various species and also individual differences within species, as with bold or cautious violets.

There is still a lot to learn, and keeping an open mind about the internal life of plants, how they work and what they process, is totally justified. Plants make up a large part of our magnificent planet and deserve to be recognized and respected for who and what they are.

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