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Back in 2006, a scientific paper put forward the idea of “plant neurobiology”, a field of study that looked to understand how plants process and react to information from their surroundings, perhaps using some sense of consciousness or even a kind of cognition and intentionality.
But now, a group of biologists looks to pour salt in the soil of this idea. Writing an opinion piece in Trends in Plant Science, the journal where the original idea was proposed in 2006, the team simply states that it's "extremely unlikely that plants, lacking any anatomical structures remotely comparable to the complexity of the threshold brain, possess consciousness.”
Although scientists and philosophers alike have attempted to come up with a framework to define the concept for centuries, consciousness remains a hazy notion. Is a squid conscious? What about an ant or a coral? When does a bundle of neurons become conscious? Do you even need neurons to acquire consciousness? Let’s not even get started on whether artificial intelligence (AI) can gain consciousness.
However, based on most criteria, the researchers argue that plants do not meet the organizational and functional complexity required.
“The biggest danger of anthropomorphizing plants in research is that it undermines the objectivity of the researcher," Lincoln Taiz, professor emeritus of molecular, cell, and developmental biology at the University of California at Santa Cruz, said in a statement.
"What we've seen is that plants and animals evolved very different life strategies. The brain is a very expensive organ, and there's absolutely no advantage to the plant to have a highly developed nervous system."
The crux of the plant neurobiology argument lies in drawing parallels between electrical signaling in plants and nervous systems in animals. Plants don’t have electro-chemical signaling neurons like us and most other animals, but they do use electrical signals and action potentials.
One of the go-to examples of this is the Mimosa pudica, or the “shy plant”, which has leaves that fold inward when they’re touched or shaken. Even Charles Darwin, the godfather of biology, compared the Mimosa to a brain receiving information from a sensory organ. As one study has shown, if you flick this plant enough times without damaging it, the leaves will eventually stop curling up, suggesting it is counting the flicks and learning they're not a threat.
At first glance, this certainly looks a lot like habituation, a form of learning where there’s a decrease in response to a stimulus after repeated presentation. However, Taiz argues this isn’t the case, citing that the experiment didn't have the necessary controls, perhaps isn't repeatable, and doesn’t rule out simple sensory adaptation.
“There is no evidence that plants require, and thus have evolved, energy-expensive mental faculties, such as consciousness, feelings, and intentionality, to survive or to reproduce,” the authors write in their piece. “Plant development and behavior can be regarded as a series of consequences emerging from internal and external signaling networks that have evolved through natural selection.”
However, rest assured, the plant neurobiology debate is no doubt far from over.
