DID YOU KNOW that plants communicate with each other through the biochemical cues emitted by their roots? That, when attacked, they produce the same substances that function as painkillers in animals and humans? That they can distinguish blue colors from red in their environments, and their kin from a plant of a different species growing nearby?
The current scientific paradigm shift in our understanding of plants is comparable in its magnitude and significance to what, at the end of the 18th century, Immanuel Kant called “the Copernican Revolution” in philosophy. With the discovery that the Earth revolved around the sun, and not vice versa, the original Copernican Revolution in astronomy signaled the end of the Ptolemaic geocentric model. The Kantian turn accomplished something similar for philosophy. Instead of the traditional focus on objective reality and the ontological question “What is X?” Kant proposed a reorientation toward the subject of knowledge and inquired into the conditions of possibility for, as well as the limits to, human knowing.
What are the reasons for including recent discoveries in the field of plant signaling and behavior, or plant neurobiology, in this illustrious list of revolutions? Philosophers of biology have often insisted on the special status of the discipline among the sciences. In different ways, Henri Bergson and Hans Jonas argued that, unlike physics or chemistry, biology and evolutionary theory do not obey “objective” laws, because life introduces a fair degree of indeterminacy into matter. The minimal interpretation of this claim is quite banal: it simply means that biology is not, and never can be, an exact science. What we are after, however, is the full sense of biological exceptionalism. Taken to its logical conclusion, the irreducible indeterminacy of biology implies that every form of life is not a totally predictable object of study, but a subject in its own milieu. Or, as Kant put it in his Critique of Judgment: “there will never be a Newton of a blade of grass.”
A century ago, the German biologist Jakob von Uexküll applied this insight to the worlds of animals. Even when the environment is objectively the same, he argued, the animal species that populate it selectively make sense of those aspects that are conducive to their survival, while safely ignoring all others. With time, von Uexküll’s writings influenced such crucial 20th-century philosophers as Martin Heidegger, Ernst Cassirer, Maurice Merleau-Ponty, Gilles Deleuze, Max Scheler, and Georges Canguilhem. But his theory of biological “perception signs” (Merkzeichen) did not extend to the world of plants, which remained relegated to the backdrop for the drama of animal life.
Today, we are still living with the repercussions of this oversight. In some progressive theoretical circles, anthropocentrism has given way to zoocentrism, such that animal life has become firmly established among the top philosophical concerns. Without denying the value of these investigations, we may conclude that a new decentering is afoot, this time announced from the margins of life occupied by plants.
When I say “the margins of life,” I am not talking about the scarcity of plants on the planet; on the contrary, vegetal cellulose is the most common organic compound on Earth. The marginality of plants has been conceptual, not empirical, as they have been imagined throughout the history of Western philosophy only in the shape of “deficient animals,” or “matter organized for reproduction.” Given this millennia-old bias, the plants’ transition from the margins to the center of thought would truly constitute a Copernican Revolution in botany, as well as in philosophy.
Let me be perfectly clear: the idea that plants are intelligent living beings is not a veiled attempt at anthropomorphizing our “green cousins.” Such a theoretical move would only leave intact — if not strengthen — our current anthropocentrism, extending its effects to living beings that have been situated relatively far from anthropos (the human), which is analogous to the Earth in the Ptolemaic system. The point is, rather, to argue that human intelligence, much like that of animals and plants, is a response to the problems each life form in question faces. As I write in my book Plant-Thinking: A Philosophy of Vegetal Life: “The sensitivity of the roots seeking moisture in the dark of the soil, the antennae of a snail probing the way ahead, and human ideas or representation we project, casting them in front of ourselves, are not as dissimilar from one another as we tend to think.”
The intelligence of plants is not merely a shadow of human knowing, and their behavior is not a rudimentary form of human conduct. After all, unlike animal and humans, for whom behavior is most often associated with physical movement, plants behave by changing their states, both morphologically and physiologically. An honest approach to the capacities of plants thus requires a simultaneous acknowledgement of the similarities and differences between them and other living beings.
In scientific circles, there is certainly no consensus on the implications of new research data drawn from the behavior of plant cells, tissues, and communities. On the one hand, the opponents of the Copernican Revolution in botany claim that the data do nothing but exemplify what has been known all along about plant plasticity and adaptability. This is the position expressed in the open letter to the journal Trends in Plant Science, signed in 2007 by 36 plant scientists who deemed the extrapolations of plant neurobiology “questionable.” On the other hand, we have the investigations of kin recognition in plants by Richard Karban and Kaori Shiojiri; of plant intelligence by Anthony Trewavas; of plant bioacoustics by Stefano Mancuso and Monica Gagliano; of the sensitivity of root apices as brain-like “command centers” by František Baluška and Dieter Volkmann; of plant learning and communication by Ariel Novoplansky; and of plant senses by Daniel Chamowitz, among many others. Their peer-reviewed research findings no longer fit within the scientific framework where plants are studied as objects, rather than living organisms. Leaving aside the provocative analogies they suggest between plants and animals, doesn’t the drastic change in approach (from plants as objects to plants as subjects) amount to a veritable Copernican Revolution, or Kuhnian paradigm shift, in botany?
It is not the role of philosophy to provide botany with inflexible and technical definitions of the mind, intelligence, learning, and other related terms that might or might not apply to the life of plants. Instead, we can imagine and work towards a creative symbiosis of philosophy and botany, where philosophical concepts would be destabilized upon contact with cutting-edge research in plant sciences, and where plant sciences would, in turn, resort to philosophy in their search for an appropriate theoretical framework. Such rigorously interdisciplinary thought would belong somewhere between a philosophy of botany and a botany of philosophy; it would discuss how plant processes, as well as vegetal images and metaphors, exert a formative influence on thinking. “Plant-thinking” demarcates this in-between space in the hopes of promoting a cross-pollination of philosophy and plant sciences.
“Out of the crooked timber of humanity,” Kant famously wrote in his 1784 Idea for a General History from a Cosmopolitan Perspective, “no straight thing was ever made.” Perhaps it is time now for philosophy to adopt a new perspective, and to begin to think beyond the human, for the “crooked timber of humanity” to learn to communicate with the magnificent woods that surround us.