Plant Neurobiology: “Foolish distraction” or “new science”?


Michael Pollan, author of Omnivore’s Dilemma and other books, has written an interesting article on The Intelligent Plant in The Atlantic. He begins by recounting the ruckus in the scientific community following the 1973 publication of the “The Secret Life of Plants.” Over the years, most of the claims in the book were discredited. However, the issue has surfaced again, this time with more scientific evidence. Stated simply: Are plants “intelligent” and should the corresponding field of study be called “plant neurobiology?”

Among the arguments for a plant intelligence:

“Plants are able to sense and optimally respond to so many environmental variables—light, water, gravity, temperature, soil structure, nutrients, toxins, microbes, herbivores, chemical signals from other plants—that there may exist some brainlike information-processing system to integrate the data and coördinate a plant’s behavioral response. The authors pointed out that electrical and chemical signalling systems have been identified in plants which are homologous to those found in the nervous systems of animals. They also noted that neurotransmitters such as serotonin, dopamine, and glutamate have been found in plants, though their role remains unclear.”

According to Yale professor Clifford Slayman of the opposing camp: "Plant intelligence’ is a foolish distraction, not a new paradigm.”

Pollen writes:

“Many plant scientists have pushed back hard against the nascent field, beginning with a tart, dismissive letter in response to the Brenner manifesto, signed by thirty-six prominent plant scientists (Alpi et al., in the literature) and published in Trends in Plant Science. ‘We begin by stating simply that there is no evidence for structures such as neurons, synapses or a brain in plants,’ the authors wrote. No such claim had actually been made—the manifesto had spoken only of ‘homologous’ structures—but the use of the word ‘neurobiology’ in the absence of actual neurons was apparently more than many scientists could bear.”

Pollen surmises:

 “The controversy is less about the remarkable discoveries of recent plant science than about how to interpret and name them: whether behaviors observed in plants which look very much like learning, memory, decision-making, and intelligence deserve to be called by those terms or whether those words should be reserved exclusively for creatures with brains.”

Stefano Mancuso a plant scientist at the International Laboratory of Plant Neurobiology in Florence provides a different perspective and views plants as a “a great symbol of modernity” since they are

“organized around systems and technologies that are networked, decentralized, modular, reiterated, redundant—and green, able to nourish themselves on light…. their brainlessness turns out to be their strength, and perhaps the most valuable inspiration we can take from them.”

While I find the work on “plant intelligence” fascinating, labeling the field as “plant neurobiology” is clearly incorrect. Ramon y Cajal laid the foundation of modern neuroscience through his discovery of the neuron and the interconnectedness of neurons, a profound natural discovery now known as the “neuron doctrine”. Plants, though possibly intelligent (depending on the definition) have no neurons, a unique component of the animal nervous systems.

Perhaps the controversy should be viewed in a wider context. Plants are not animals, however, they certainly are more complex than previously believed. There should be a wider term that encompasses complex life that has arisen on Earth whether plant or animal. And, as Pollen notes, prepares us with a wider conception of intelligent life should we “contact” living things in other worlds.

As Pollan concludes, if you define “intelligent behavior” as “the ability to adapt to changing circumstances” then “plant intelligent behavior” should replace “plant neurobiology.” Even critic Slayman concedes: 

“Yes, I would argue that intelligent behavior is a property of life.”

John Oró, MD