The Inner Lives of Plants: Cognition, Sentience, and Ethics

Late last year ago I posted an interview with the editors of a book titled The Mind of Plants: Narratives of Vegetal Intelligence. It was quite popular and generated a large number of emails asking me questions about plant intelligence, consciousness, and sentience and also stories from people who had witnessed what they called learning, thinking, and feeling in a wide variety of "smarty plants." An email I received from Brad asked, "Given what we know, should we thoughtlessly be mowing lawns and chopping down trees?" Madeline wanted to know, "What will it mean if and when we learn that plants are sentient, feeling beings? Is it okay to eat them?"

Two weeks ago I read an essay called "The radical new experiments that hint at plant consciousness" by Natalie Lawrence that nicely summarizes what we know in a growing field called "plant neurobiology"—how plants process information—and points to where more research is needed as we learn about their intelligence, behavioral plasticity, personalities, and much more.

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

• Plants are susceptible to anesthesia; lidocaine applied to roots works well to knock out plants.
• Plants have social lives; they communicate with each other, react to what's happening to them and around them, and interact with other species including nonhuman animals (animals). For example, chemicals released by tomato plants encourage caterpillars to cannibalize one another.
• Plants display cognition—flexible and goal-directed behavior. When climbing a pole, a clever bean makes "broad, circular sweeps of their surroundings, growing as they go. As they home in on a pole, some beans will suddenly lunge towards it like a drunken pub-goer taking a swing at someone. It is a rapid, directed change in behavior. This suggests the plant isn’t simply running a pre-programmed pole-seeking sequence." Researcher Paco Calvo who works at the Minimal Intelligence Laboratory at the University of Murcia in Spain, suggests this might show that the bean knows the pole is there but he cautions we need more research. He and his colleagues have shown that lunging by beans is accompanied by spikes in electrical activity, hinting at a possible "level of sentience" by brainless plants.
• Plants may be conscious. Calvo believes the flexible behavior displayed by plants suggests that they may have "unique, subjective experiences." When the ways in which plants grow are combined with the fact they have electrical signaling, it's reasonable to posit they have some type of consciousness, possibly explained by what's called integrated information theory. This theory views consciousness as the capacity to integrate different aspects of experience into a whole.
• Plants can learn and remember. One study showed plants can learn to grow toward a breeze, sort of like Pavlovian conditioning shown by dogs. However, there is a good deal of debate about how robust these data are because of failures to replicate the findings. (More information can be found here.)
• Plants have personalities. Based on "genetic hardwiring and behavioral flexibility," individual violets can be labeled bold or cautious depending on how long they fold their leaves after being touched.
• Domesticated plants tend to be "less canny and independent" than wild relatives. Lawrence writes, "Wild vines, for example, can scour their surroundings for something to climb and rapidly scale up it. In contrast, domesticated vines flounder unless they have trellises or poles placed next to them. You might think of them as the pampered lapdogs of the plant world." When domestic plants go wild, they behave more like wild members of their species. (Domesticated animals tend to be more docile than their wild relatives.)

Where to from here?

Needless to say, there is a lot of 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 The emails from Brad and Madeline about what it means if plants are sentient and have feelings show there also are important ethical issues that need to be considered.

The amount of sustained interest in the inner lives of plants by highly credentialed scientists tells me "there is something there," and I look forward to more studies on the fascinating minds of a wide variety of flora. It wouldn't be surprising if we learn there are differences between various species and also individual differences within species, as there are with bold or cautious violets.

There is still much to learn, and keeping an open mind about the inner lives of plants—how they work and what they're processing—is fully warranted. Plants make up a large portion of our magnificent planet and deserve to be recognized and respected for what and who they are.