“How do they know where to go?”
My mother and I asked this question repeatedly last summer as we tried (in vain) to control the spread of the morning glories we planted. The vines of these lovely flowers grew faster than weeds, spreading across the ground, climbing along the branches of a dead bush, and reaching up to cling onto the tips of a nearby evergreen. No matter how much we tried to reroute or trim down the vines, they always stretched for the tree. It was as if the morning glories knew what they wanted and refused to be deterred.
We figured this “observation” was just us personifying a plant, but it turns out botanists have long wondered whether plants could have wants or goals as well. In a study published in the journal Scientific Reports last November, researchers explored whether the vine-like French bean plants were purposely seeking structures to climb or simply reacting to their environment.
“The question is, are they showing goal-directed behaviours consistent with anticipation and fine-scaled tweaking of their movements, as they approach?” study co-author Paco Calvo explained to The Guardian. To figure out the answer, the research team set up an experiment to see if they could observe whether these plants showed an intent to move.
Testing the Thoughts of a Plant
Twenty French bean plants, grown by the researchers for the experiment, were randomly placed into two different booths: one contained a support pole while another had nothing in it. The air circulation, temperature, and light source of both booths were the same.
The scientists then set up time-lapse cameras in each booth. They used the recording from the cameras to observe the plants as they grew. What they found was that the plants in the booth with a pole grew in a more direct and predictable path towards it — a contrast to the plants in the booth without the pole. The team believed this was an indication of the plants showing intent to reach for a support.
“This isn’t just adaptive behaviour,” Calvo told The Guardian, “it’s anticipatory, goal-directed, flexible behaviour.”
But not everyone agrees.
The Great Debate on Plant Consciousness
The experiment has stirred up reminders of a years-old debate among scientists about whether plants are capable of having thoughts, intents, and feelings. Plant biologist Dr. Lincoln Taiz is one researcher who has been very outspoken against the belief that plants have a consciousness.
“The biggest danger of anthropomorphizing plants in research is that it undermines the objectivity of the researcher,” he stated in a news release about his 2019 study reviewing the legitimacy of the ‘plant neurobiology’ field.
In his paper, straightforwardly titled “Plants Neither Possess nor Require Consciousness,” Dr. Taiz and his co-authors pushed back on plant neurobiology — a field that established itself in 2006. Ever since plant neurobiology became a thing, proponents of the field have made headlines discussing the possibility of plant-thinking or a plant version of thinking.
But Dr. Taiz and his team argued that plants didn’t fit any scientific definition of having intelligence, cognition, or consciousness. Instead, they believed plant neurobiologists were observing a form of plant signaling; the way plant cells ‘signal’ to each other to react to a stimulus or their environment. (It’s how plants know when to flower, emit chemicals when harmed, open their leaves for the sun, and grow without the existence of a central nervous system or brain.)
The authors also suggested that people were oversimplifying the complex nature of the brain in order to make plants appear as equally thoughtful as animals. Furthermore, they continued, it simply didn’t make sense for plants to evolve to think or form a consciousness. Plants have already evolved to be “paragons of energy efficiency” by “converting sunlight, carbon dioxide, and water into the complex carbon compounds” that make up all living organisms. They didn’t need consciousness to be better at what they already do.
In fact, the writers noted, brainpower actually uses up a bunch of energy. Animals constantly have to balance out their limited energy and the necessity to hunt, escape predators, or woo picky mates.
“What we’ve seen is that plants and animals evolved very different life strategies,” Dr. Taiz continued in the press release. “The brain is a very expensive organ, and there’s absolutely no advantage to the plant to have a highly developed nervous system.”
To Think or Not to Think?
Is Dr. Taiz being a spoilsport or a realist? Other researchers have refuted opponents to plant neurobiology by suggesting that plant “intelligence” might look different from mammalian intelligence. They insist that their peers shouldn’t dismiss the possibility of plant thought completely.
Although Calvo admitted to The Guardian that his experiment wasn’t the nail in the coffin for proving plant intent or consciousness, he urged more research into the debate rather than immediate disregard. “If successful,” he wrote in an unpublished paper provided to the publication, “these experiments could position plants as the next frontier in consciousness science, and urge us to rethink our perspectives on consciousness, how to measure it, and its prevalence amongst living beings.”
“Indeed, by comparing plants with organisms with mental processes that look like our own, have we made it impossible to recognize a consciousness different to ours?” pondered Stuart Thompson, a senior lecturer on plant biochemistry, in a rebuttal to Dr. Taiz’s paper.
The debate is sure to continue for more years to come. In the meantime, unfortunately, my mother and I had to uproot and pull out all the morning glories that had grown out of our control. Whether the vines were intelligent or not, we had to acknowledge one thing: They definitely “outsmarted” us.
Nature on Plex: