Triptych image: Megan Cotts, "ECU"
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 co...read more