Uncovering Plant Intelligence
My interest in the topic of “plant intelligence” was first piqued when I read about Darwin’s work on plant movements and his drive to find out if plants had “free will”.
Darwin’s meticulous diagram illustrates the circumnutation of the upper internodes of the common pea plant (Pisum sativum), showcasing the intricate, directional movements plants make in response to internal growth patterns and external stimuli. From The Power of Movement in Plants(1880)
While many scientists of the 18th and 19th century contemplated the existence of consciousness and intelligence in plants, the biggest contributor at the time was Charles Darwin. In 1880, Charles Darwin collaborated with his son Francis and wrote a book called “The power of movements in plants” (Darwin, 1880). This rich scientific prose contained a plethora of experiments accompanied by carefully traced diagrams with the aim of exploring various plant behaviours such as phototropism, gravitropism, thigmotropism, and circumnutation. Darwin hoped that by publishing his experiments on plant movements he could elevate their status from passive immobile autotrophs to highly adaptive and organised living organisms. He believed that these plant movements proved that plants act with purpose and can be goal – oriented to survive (Darwin, 1880). It is most important to note that Darwin proposed his famous “root-brain” hypothesis in this book. Darwin’s observations led him to believe that root tips were responsible for plant movement to stimuli, thus likening them to the brain of an animal (Darwin, 1880).
“It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.” (Darwin, 1880, p.574).
Jagadish Chandra Bose – hailed as the “Father of plant neurobiology”
Another prominent scientist whose revolutionary work in Plant Electrophysiology should be talked about is Jagadish Chandra Bose. Bose spent the first phase of his scientific career as a physicist, making ground-breaking discoveries in radio physics and wireless telegraphy, being the first person to use semiconductors for radio wave detection (Das, 2024).
By 1901, Bose shifted his focus to plant physiology as he wanted to better understand the connection between animate and inanimate matter. Having studied under the guidance of Francis Darwin, Bose’s plant research was deeply rooted in Darwinian botany and the principle of Natural selection. Bose expanded on Darwin’s root-brain hypothesis by studying the electrical impulses involved in plant roots and stems (Schlegel-O’Brien, 2019)
During this time, he invented around 50 instruments that he to measure plant physiology, the most remarkable on being the crescograph, a magnetic device used to amplify plant movements for accurate measurements (Minorsky, 2021). What’s most impressive about his work is his ability to create an interdisciplinary connection between physics and biology by inculcating the principles electromagnetism to study and quantify electric pulsations in plants.
“The barriers which separated kindred phenomena in the plant and animal are now thrown down. Thus, community throughout the great ocean of life is seen to outweigh apparent dissimilarity. Diversity is swallowed up in unity.” – Jagadish Chandra Bose (Brown, 2016, p.4)
A large amount of Bose’s work was centred around the plant Mimosa pudica and its rapid leaf movements (Minorsky, 2021). By proving that he could measure electrical impulses in these plants, he suggested that these were like action potentials present in animal nerve cells.
In another experiment involving the plant Codariocalyx motorius, Bose compared its oscillary leaf movements to a beating heart. For whatever reason Bose seemed reasonable, he subjected this plant to external stimuli like cold, general anaesthesia and low oxygen. These studies revealed that the oscillary movements of this plant’s leaf were inhibited upon being subjected to these stimuli (Minorsky, 2021).
Despite Bose’s academic rigour and pioneering work in plant physiology (for which he received his Knighthood in 1917), he faced a sea of opposition from western scientists (Minorsky, 2024). In fact, several science journals, including Nature, rejected to publish his work, forcing him to self-publish utilising Indian outlets. Smear campaigns by American scientists against Bose’s work included the themes of incompetence, mysticism and fraudulence, forcing his research to fall into oblivion for the rest of the 20th century, pushing back the study of plant Electrophysiology by decades (Minorsky, 2024).
“Knowledge is never the exclusive possession of any particular race nor does it recognise geographical limitations. The whole world is interdependent and a constant stream of thought had been carried out throughout the ages enriching the common heritage of mankind.”
– Jagadish Chandra Bose (Brown, 2016, p.14)
Minorsky (2024) suggests that western intellectuals were raised on the principle of Aristotle’s Scala Naturae, a hierarchal construct to rank all living being from simplest to most complex. It’s no surprise to know that Aristotle put humans at the top and non-living matter at the bottom. This understanding of evolution placed humans at the top of the scale. This exalted position combined with the Judaeo-Christian belief of man being made in the image of God may have created an obnoxious mindset and view towards exploring complex concepts like conscious and intelligence in plants.
This opinion can further be backed by socio-religious research (Ardi, Budiarti, 2020) suggesting that people expressing narcissism and religious fundamentalism are more likely to exhibit reduced inclusivity towards individuals of different religious backgrounds.
Nevertheless, plant neurobiology has been a very controversial field since the beginning.
Many mainstream biologists believe that the term “plant neurobiology” is incorrect as plants do not have neurons like animals do (Alpi, et al. 2007). So, if a field of study includes the prefix “neuro” in its name, isn’t it obvious that the main subject of research should have neurons and neural pathways? But what if plants have neuron-like structures of their own? Maybe they have specialised cells and tissues that have the same functions as neurons? And how can we prove this?
To answer these exact questions and many more, a new field called “plant neurobiology” was born. The purpose was to deviate from the mainstream thought process and methodologies of studying plant behaviour and establish an interdisciplinary approach to uncover the truth behind plant intelligence.
In 2005, The Society for Plant Neurobiology was created by a group of like-minded scientists who wanted to explore plants as “information processing organisms” (Minorsky, 2024). Their united goal of establishing an interdisciplinary approach of study led them to launch their Journal, Plant Signaling & Behavior. There was strong opposition to this work, most prominently from Alpi et al.’s (2007) paper – “Plant neurobiology: no brain, no gain?”
This debate became so polarised that the society changed its name to “Society for Plant Signaling and Behavior” to promote global acceptance.
The central theme of opposition in this paper was to emphasize the fact that plants do not possess neurons and to criticize proponents of plant neurobiology to propagate this harmful narrative (Alpi, et al. 2007).
Proponents of plant neurobiology believe that this argument is flawed because Plants and animals belong to two different kingdoms, so why do we need to define plant intelligence the same way we define animal intelligence? According to the proponents, we must move past this zoo centric thought process and embrace new ideas (Calvo Garzon, 2007). Another proponent, Monica Gagliano, suggests that instead of focusing on animal-centric intelligence concepts on plants, we should view them as information-processing systems (Calvo Garzon, 2007). In this way, we can move on from this debate of whether or not plants have neurons/nervous systems but rather focus on studying plant behaviours and asking questions regarding how they process information. Calvo Garzón (2007), shares the same view; he believes that a “fight over labels” needs to end. Additionally, he suggests that the debate over whether plants exhibit intelligence like animals do should be replaced with an inquiry into whether animals and plants have computational capabilities (Calvo Garzon, 2007).
Another though-provoking point in this debate was put forth by Anthony Trewavas, in his response to Alpi, A. et al. (2007). He clearly states that plant neurobiology has always been used as a metaphor by plant neurology proponents. He believes that it is necessary to give way to such metaphors so that the scientific community can investigate complex problems with a creative and imaginative outlook. In this way, metaphors are not misleading, but substantially valuable tools that can be used to propel neurobiology research (Trewavas, 2007).
On the other hand, some other researchers have suggested that the definition of a nervous system should be broadened so that we can study the mechanisms of neurology from an evolution perspective, moving away from the common zoo-centric approach (Segundo-Ortin, Calvo, 2023).
While some opponents of plant neurobiology have expressed concerns with regards to spreading misinformation to younger disciples, others have crossed the line of basic decorum by describing the plant neurobiology debate as something “between the scientific community and the nuthouse” (Minorsky, 2024, p.2)
Minorsky (2024) also points out that all 36 signatories involved in the Alpi et al. (2007) paper were in the West, suggesting that they may be experiencing the phenomenon of “phytoneurophobia”, a deeply rooted apprehension towards plant neurobiology. The author suggests that this may have originated from many different aspects of their lives such as geography, education and socio-political climates.
Sentience
It has been well established that humans and some other animals are sentient or possess some degree of sentience. Since we cannot directly investigate the mental states of animals, we must rely on indirect evidence to prove animal sentience (Segundo-Ortin, Calvo, 2023). For example, if an exploratory study is being performed to detect the feeling of pain in an animal, we will most likely compare if the animal exhibits the same behaviour has human behavioural responses to pain. Plants may not have the same pain receptors as some members of the Animal Kingdom do but they have molecular responses such as defence signalling as a response to stress or injury. In this way, we can say that plant defence behaviour and animal defence behaviour serve the same overall function of protection and healing, the only difference is that animals may feel pain while the same is not yet proven in plants (Segundo-Ortin & Calvo, 2023).
We already know that animals such as octopi experience sentience, but what about lower-level organisms such as insects? A growing body of behavioural and electrophysiological studies on insects are providing evidence that certain insects can experience sentience (Klein& Barron, 2016).
It’s clear to me that the further away we perceive a life form to exist from humans, the more sceptical we become about them experiencing sentience or any form of intelligence.
While we have explored the different narratives and arguments weaved by the opponents and proponents of plant neurobiology research, I think it’s time to move on to actual scientific breakthroughs in this field.
In continuation of my efforts to uncover the meaning of plant intelligence, my next article will cover different types of scientific breakthroughs involving plant physiology and behaviour. The results of these studies and their inferences will help create the case for the question “do plants exhibit signs of intelligence?”
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14. Trewavas, A. (2007). Response to Alpi et al.: Plant neurobiology – all metaphors have value. Trends in Plant Science, 12(6), 231–233. https://doi.org/10.1016/j.tplants.2007.04.006
