A few years ago I attended a conference where some apparently serious people debated whether plants had consciousness. To me this seemed absurd, given that consciousness is a product of neural systems in general and brains in particular. While I’ve never had any problem attributing consciousness to animals, plants seemed a domain or kingdom too far. Without neural systems or brains, how could they have consciousness? They can’t, at least if we adhere to traditional definitions of consciousness, sentience, and intelligence.
But if we acknowledge, as we must, that plants are living organisms with whom we share a common ancestor going back billions of years, then the notion of asking a Nagel-like question (What is it like to be a plant?) makes good sense. While most of the speakers at the conference I attended were starry-eyed mystics, neo-pagans, and pantheists, one was a harder-nosed scientist. She discussed recent research into plant “behavior” and it sounded fascinating. So I did some skeptical reading in this nascent field and came away impressed. Plants are far more interesting than I had supposed or imagined.
Several studies have shown that plants can recognize and favor kin. Impressive as this is, it’s nothing compared to the possibility that some plants have memory and are capable of learning. While this sounds incredible, check out this excerpt from an article that Michael Pollan just published in the New Yorker:
The most controversial presentation was “Animal-Like Learning in Mimosa Pudica,” an unpublished paper by Monica Gagliano, a thirty-seven-year-old animal ecologist at the University of Western Australia who was working in Mancuso’s lab in Florence. Gagliano, who is tall, with long brown hair parted in the middle, based her experiment on a set of protocols commonly used to test learning in animals. She focussed on an elementary type of learning called “habituation,” in which an experimental subject is taught to ignore an irrelevant stimulus. “Habituation enables an organism to focus on the important information, while filtering out the rubbish,” Gagliano explained to the audience of plant scientists. How long does it take the animal to recognize that a stimulus is “rubbish,” and then how long will it remember what it has learned? Gagliano’s experimental question was bracing: Could the same thing be done with a plant?
Mimosa pudica, also called the “sensitive plant,” is that rare plant species with a behavior so speedy and visible that animals can observe it; the Venus flytrap is another. When the fernlike leaves of the mimosa are touched, they instantly fold up, presumably to frighten insects. The mimosa also collapses its leaves when the plant is dropped or jostled. Gagliano potted fifty-six mimosa plants and rigged a system to drop them from a height of fifteen centimetres every five seconds. Each “training session” involved sixty drops. She reported that some of the mimosas started to reopen their leaves after just four, five, or six drops, as if they had concluded that the stimulus could be safely ignored. “By the end, they were completely open,” Gagliano said to the audience. “They couldn’t care less anymore.”
Was it just fatigue? Apparently not: when the plants were shaken, they again closed up. “ ‘Oh, this is something new,’ ” Gagliano said, imagining these events from the plants’ point of view. “You see, you want to be attuned to something new coming in. Then we went back to the drops, and they didn’t respond.” Gagliano reported that she retested her plants after a week and found that they continued to disregard the drop stimulus, indicating that they “remembered” what they had learned. Even after twenty-eight days, the lesson had not been forgotten. She reminded her colleagues that, in similar experiments with bees, the insects forgot what they had learned after just forty-eight hours. Gagliano concluded by suggesting that “brains and neurons are a sophisticated solution but not a necessary requirement for learning,” and that there is “some unifying mechanism across living systems that can process information and learn.”
This is fascinating stuff, even if it is potentially nightmarish for ethical vegans.
Pollan’s piece, “The Intelligent Plant,” is a superb and comprehensive introduction to this field. It’s long but well worth your time and attention.