A vast meadow of nemophilia, in Japan 

You’ve heard of Artificial Intelligence (AI). What about Biological Intelligence (BI)? The academic discipline of plant biology is being rattled by daring claims that intelligence exists on a continuum, from bacteria, to radishes, to slugs, to chipmunks and ultimately to humans. “Intelligence is a property of life”, says one expert on BI.

For a perspective on this surprisingly contentious topic, MercatorNet consulted Professor Ulrich Kutschera (left). He has just published a 712-page textbook entitled “Physiology of Plants. Sensible Vegetation in Action”, January 2019 (in German), with hundreds of images, and references to his own work as an experimental plant biologist. A long chapter is dedicated to plant intelligence.

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MercatorNet: Some biologists hold that plants have cognitive abilities, including perception, learning processes, memory and consciousness. Is this a minority view?

U. Kutschera: As an Associated Editor of the US journal Plant Signaling & Behavior I am in contact with plant biologists who argue that land plants are intelligent beings, similar to “lower animals” like leeches and earthworms. I have studied these creatures over the past 40 years (see MercatorNet, “An evolutionary biologist dissects gender theory”) and therefore feel competent to discuss this issue from a “zoo- and phyto-centric” perspective.

In my judgement, the majority of plant scientists do not accept the notion of plant intelligence, as well as the related claim of a “dignity of plants”. However, these are interesting philosophical aspects pertaining to plant life, which should be discussed and evaluated from a scientific perspective.

MercatorNet: Supporters of Biological Intelligence argue that if this property is the ability to adapt to changing environments, then plants are clearly intelligent. How do you respond?

U. Kutschera: The key point is that there are numerous definitions of “intelligence”, so that even psychologists cannot define this term unequivocally (1). Plant biologists who attribute this key characteristic of apes and humans to the “green world” usually argue that intelligence can be equated with “the ability to solve problems” (2). If we accept this definition, then leeches and earthworms (which have a miniaturized brain) are intelligent and according to this logic, brain-less vegetation is also “intelligent”.

MercatorNet: OK, it’s clear that plants don’t have brains that we have, a blobby sack of neurons protected by our skull. But couldn’t you define intelligence as a distributed network, rather like Artificial Intelligence?

U. Kutschera: This definition exists in publications of proponents of plant intelligence, as described in my book (1). If we study the extensive root system of a typical land plant, so the argument goes, we can imagine that all of the root tips – millions of tiny organs – represent a kind of distributed, sensitive network, analogous to AI. This view of a subterranean organ system that “searches” the soil for water and mineral nutrients, makes some sense.

MercatorNet: If plant intelligence were accepted, what does that mean about being human? Is this the ultimate de-throning of Homo sapiens in the process which was kicked off by Darwin?

U. Kutschera: I have argued in the corresponding chapter of my textbook that the ability to solve problems (i.e., one of many definitions of intelligence) is clearly a property of all living beings – bacteria, slime molds, earthworms, algae, plants, apes and humans manage to survive and reproduce. However, a creative human being (scientist, artist, etc.) may not have perfected his ability to “solve his practical problems of life”, whereas a much less creative routine worker (clerk, salesman, etc.), will be superior in this respect. Hence, if we equate intelligence, at least in part, with creativity (1), the definition used by adherents of “plant intelligence” becomes meaningless. Despite the fact that Charles Darwin, in his 1880 book on plant movements, was the first to compare the tip of a seed plant with the brain of a “lower animal”, which marks the starting point of the plant intelligence movement, our own species still remains unique. Some humans create music, artwork, literature and scientific books. No ape species has as yet been discovered which has been endowed with this creative capability.

MercatorNet: And what about the ethics of dealing with plants?

U. Kutschera: This is a serious issue which is related to plant intelligence. In April 2009, the Swiss Parliament discussed the topic of “plant ethics” and proposed to attribute to plants a kind of “Würde”, which can be translated as “dignity” (3). As a consequence, some radical plant ethics-activists have distributed T-shirts and other propaganda material with the slogan “Salad is murder”. Despite the fact that plants are sensitive, valuable, living beings, this agenda is questionable. I would go so far as to label it, in its extreme form, as part of a growing European pseudoscientific-esoteric movement.

MercatorNet: Do we need an updated Peter Singer to defend the rights of plants?

U. Kutschera: Despite my reservations to interpret plants as intelligent beings with dignity, I agree with Peter Singer that plants should be considered, with respect to humans, as valuable and equal organisms – current end-points of organismic evolution, which started some 3.8 billion years ago. They should be protected and not destroyed, because they are our “evolved cousins”, and, moreover, photosynthetic organisms. Without green plants, life on Earth would not exist. Plants provide our food (all meat was grass), the oxygen we breath, wood for constructing houses, fibers for clothing, and a green environment to stay psychologically healthy.

Wheat seedling and adult plants in a changing world, Figure 312 reproduced from the textbook “Physiology of Plants, 2019

MercatorNet: How can you explain the high sensitivity and remarkable behavior of plants, such as shade-avoidance, communication with peers etc.?

U. Kutschera: As mentioned above, plants are very complex living beings that function according to the principles of physics and chemistry. They carry a heritable genetic program (the genome), and have evolved adaptations to survive and reproduce in an inhospitable world. In other words, as sessile organisms, plants are constantly challenged by the environment. They cannot run away to escape predators; accordingly, they defend themselves via “chemical weapons” (i.e., secondary biomolecules stored in specific cell compartments). To achieve their autotrophic nutrition and growth, plants absorb mineral salts (dissolved in water in the soil), transport nutrients throughout their body, carry out photosynthesis and respond to changes in their environment.

My explanation for shade avoidance, plant communication with conspecifics, or via root-associated fungi etc., is straightforward. Only those individuals in variable populations of plants that were by chance (via sexual genome-reshuffling and heritable mutations) adapted to changing environmental conditions, survived and reproduced. Most of their competitors were destroyed by predators, etc. The outcome of this evolutionary “struggle for life” is what is “left over” in the biosphere today: the best adapted individuals, which represent the members of extant (variable) populations of those plants that grow in natural ecosystems.

MercatorNet: In your book, you describe the work of the founder of plant physiology, Julius Sachs (1832–1897) and explain the importance of his work. However, science progresses at a high pace, so why is Sachs still being discussed today?

U. Kutschera: Human beings are clearly equal by law, but they have not evolved as genetically identically clones. In other words, all men and woman in a population of our species are different – concerning their outer appearance (phenotype), genetically, and with respect to inherited capabilities.

Like Charles Darwin, Julius Sachs was an outstanding scientist, whose inborn genius forced him, as a workaholic, to devote his entire life to science. As I have shown in my book (1), most of the insights and theories that he proposed 150 years ago are still valid, despite the fact that the biological sciences are characterized by an unimaginable progress (each year, thousands of high-quality research papers are published). Darwin and Julius Sachs are icons of biology.

MercatorNet: You are afraid that the attribution of intelligence to plants may support people interested in the occult and esotericism who promote pseudoscientific claims. Why?

U. Kutschera: In my book, I have argued like Sachs that plants are evolved living beings without a nervous system and a brain, but endowed with high sensitivity and complex metabolic activities. However, we should not ascribe them the capacity of intelligence (by analogy, leeches are not “intelligent worms”).

I see the danger of a further rise in occult-esoteric ideologies, which dominate, in part, German politics as well as our orthodox education system. Dogmatic anti-scientists may pick up the notion of plant intelligence and mix it up with religious belief and superstition. If we redefine key terms describing human brainpower, biology will be damaged via an invasion of uncritical thinking, in tandem with the emergence of pseudoscientific claims, similar to those made by creationists, adherents of homeopathy, etc.

MercatorNet: A last question: in your comprehensive textbook, you also discuss genetically modified organisms (GMOs) and climate change. Why?

U. Kutschera: Plants are the key green players in our biosphere. They not only provide us with food and oxygen, they also determine to a large extent our climate. Genetically modified plants are more productive and easier to handle by agriculturists than their relatives. As detailed in my textbook, they pose no harm to the environment or to consumers. Here in Germany, a majority of the population rejects GMOs, which is essentially due to political anti-Gentech propaganda. Moreover, scientific illiteracy is on the rise.

To combat this disturbing tendency, my textbook — and a new journal entitled Plants, People, Planet (4) —  may be viewed as “weapons of rationality”, as well as a new agenda of “scientific enlightenment”. Unfortunately, this naive German angst with respect to GMOs also applies to climate change. As described on many pages in my book, green plants currently remove about one-third of anthropogenic CO2 emissions. You can only discuss and understand climate warming in the light of these and other biological facts, which are based on a detailed knowledge of the life of plants (3,4).

Dr Ulrich Kutschera is a professor of evolutionary biology and plant physiology at the University of Kassel, Germany, and a visiting Scientist in Stanford/Palo Alto, CA-USA. He is not only an expert in animal evolution and behaviour, but also an experimental plant physiologist with a focus on crop species, like sunflower, maize and rice. As author of some 300 scientific publications plus 13 books on a variety of topics he has a broad knowledge in the biomedical sciences.  See Ulrich Kutschera on Wikipedia.

Notes

(1) Kutschera, U. (2019) Physiologie der Pflanzen. Sensible Gewächse in Aktion. LIT-Verlag, Berlin.

(2) Mancuso, S. (2018) The Revolutionary Genius of Plants. A New Understanding of Plant Intelligence and Behavior. Simon & Schuster, New York.

(3) Koechlin, F. (2017) Plant Whispers. A Journey through new realms of Science. Lenos Verlag, Basel.

(4) Hiscock, S. J., Wilkin, P., Lennon, S., Young, B. (2019) Plants matter: Introducing Plants, People, Planet. Plants, People, Planet, 1, 2–4. 

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Dr Ulrich Kutschera is a professor of evolutionary biology and plant physiology at the University of Kassel, Germany, and a visiting Scientist in Stanford/Palo Alto, CA-USA. He is not only an expert in...