Plants: The Stimulants of Thinking

Photograph by Selbe Lynn.


 Michael Marder

November 23, 2015


Recently, the curators of brand new center for contemporary art Tabakalera in San Sebastián have asked me to give the inaugural public lecture on the philosophy of plant stimulants. As I see it, not only tobacco leaves and coffee beans belong to this group, but also every vegetal species, from mosses and grasses to rose bushes and olive trees. Often unbeknownst to us, plants stimulate us by giving a vibrant world of smells, colors, shapes, and tastes to our senses. Above all, they undergird abstract ideation, traceable back to the most material and concrete strata of digestion and sexuality, involved in the vegetal soul (to threptikon) which enables my reproduction and renewal, be it in myself or in the other. Now, this basis remains hidden and withdrawn unless it prickles, jolts, or goads us on in an intense way. The spiritually or mentally jolting, prickling, goading plants are stimulants properly so called because of their effect on the central nervous system. Theirs, however, is the extreme case in a broad continuum of cognitive and behavioral influences the vegetal world exerts on us.

Consider, for instance, soybeans. Hardly classifiable as stimulants, they can have a profound impact on human hormonal and reproductive systems, thanks to the release of phytoestrogens, which are akin to the sex hormones in women. MicroRNA’s from rice, usually regulating plant development, survive the digestion process, persist in mammalian tissues, and manipulate the expression of animal and human genes (such as those responsible for prompting receptors in the liver to filter out LDL, or “bad cholesterol”).[i] Concentrated glucose from overcooked starchy vegetables played a crucial role in the evolution of the growing brain, with its increased metabolic demands.[ii]

In each case, consumed plants stimulate a physiological or evolutionary process or function in their human consumers. Far from fuel that passes without a trace through the body-machine it powers, plant matter interacts with — and indeed acts upon — the non-vegetal organism that receives it. Assuming that the Cartesian mind-body dualism is misguided, the same vegetal interaction with and action upon human thinking should be expected as that we experience in our corporeality. Much of my energy that went into formulating “plant-thinking” derives from this hypothesis.

As for herbal stimulants per se, they reveal the absurdity of equating plants with passivity, torpor, slowness, and deficiency. It is to certain beans and leaves that we turn when we want to quicken our heart rates, accelerate the metabolism, or encourage the rapid firing of neural synapses. We might feel sluggish and devoid of energy before that first cup of daily coffee that makes the world come into focus. In this sense, plant-derived stimulants restore the forgotten semantic dimension of the words vegetal and vegetation that, instead of referring to the unconscious condition of “the persistent vegetative state,” are associated with vigor and virility. Stimulants masculinize the otherwise feminized flora, imbuing it with the sense and connotations of power and potency. (Having emerged as a medical term in the end of the seventeenth century, stimulant originally meant “something that goads a lazy organ,” most frequently the penis.)

The gender-related polarization of plants between the vast majority of species that are feminized and the masculinized stimulants is, nevertheless, undesirable and injurious both to the environment and to ourselves. The exceptions of coffee, cacao, tobacco, coca, and so on merely prove the general rule that attributes to vegetation as a whole a passive role, while consigning to oblivion the gradual and sustained stimulation it provides for our bodies and thinking. According to Russian philosopher Vladimir Bibikhin, they represent “the revenge of the forest,” against which our civilizations have fought since their very inception. The seductive, de-civilizing forces of stimulants that undo the thin varnish of reason smeared on the human subject are nothing other than the return of the (vegetal) repressed. But the rhetoric of “revenge” (with its aggressive, militaristic and vindictive insinuations) contributes to a masculinized view of certain plants that do not go quietly into the green night, to which we consign them.

More than that, stimulants are caught up in a vicious cycle with our highly ruinous conception of energy, which knows no active rest, no end, and no fulfillment. They substantiate this conception, even as the energy of pure potentiality demands their increased use. Capitalist production — which is increasingly a production of needs, lifestyles, and desires — plugs into the circuit of stimulants and energy-as-potentiality, which explains the glowing success of corporations such as Starbucks or, previously, the tobacco companies. To be sure, the use of coca or tobacco leaves, among others, preexists capital and is widespread among the traditional societies of Latin America. But there is something in the logic of herbal stimulants that capitalist production binds its apparatus to and exaggerates. I am thinking about excess.

Unlike other plant products, stimulants do not cater to the immediate physiological requirements for nourishment. They first satisfy human desires, as opposed to needs, even if, following habituation and addiction, this desire in all its superfluity may become a need in its own right. Similarly, capital consists not so much in the value drawn from the utility of commodities, nor in their immediate exchange value, but in surplus value, over and above the material sphere of production. As surplus value, capital is the excess of what is not restituted back to the workers in the form of wage labor. The increasing margins of profit depend on the expansion of this excess, which (in the absence of state interference) is the stimulus of economic growth, itself a vegetal term automatically applied to the economy. By analogy with herbal stimulants, surplus value bestows virility, potency, or power onto those who appropriate it, without any inherent actual end in sight. And, again akin to addictive stimulants, this power can never stagnate if it is to live up to its dynamics; rates of growth are themselves supposed to grow, quarter after quarter and year after year, for the economy to be deemed healthy.

We would not find it strange that the defenders of excess, who rebel against the classical virtue of moderation, would adhere to a romanticized view of stimulants. Tenth-century Persian-born philosopher Avicenna, who liked to experiment with plants for medical purposes and who died of a celery seed overdose, famously preferred to measure the days (and the nights) of his life in breadth, rather than in length, that is to say, in the intensity of lived time instead of its extensiveness.[iii] Intensive living is, in effect, quite distinct from the empty and emptying excesses binding together the spiral of addiction and the treadmill of capitalism. When stimulants are put in the service of a life that is full and perhaps overflowing with itself, however, then they are neither pure means without an end nor transcendental ends, divorced from the finitude and fragility of our world. A question arises: what does such ethical stimulation actually entail?

Lest we lose sight of another etymological stratum of the word, the origin of the Latin stimulus is vegetal. It evokes a sharp and pointed stick, a prickle, or a sting — in any event, a defensive part or a reaction initiated by a plant. A stimulus always calls for a response, whether conscious or not. Accepting that every plant is a stimulant with respect to our bodies and minds, we are called by it to respond and, especially, to assume responsibility, which is an ongoing ethical task. The ends of this responsibility are folded into responsiveness itself, not imposed from the outside but immanently arising from our encounters with the vegetal world, from the sting or the prickle our consciousness and our conscience might experience upon contact with plants.

True: the familiar herbal stimulants (containing caffeine, ephedrine, and other substances) goad us on to engage with and respond to countless things that do not belong to the context of such encounters. Still, in these exceptional instances, stimulation is doubled, and the excitement of our sensorium and of our cognition overlays the more stable stimuli we receive from plants that, at all times, demand a response. The entwined ethico-ontological nature of my plant-thinking has been precisely this: it has put forth an archaeology of primary vegetal stimulation, repressed in the subsequent transactions with the world around us. If powerful stimulants can clearly illustrate the active role of plants vis-à-vis human subjects, then so be it. But we should never forget that the sporadic stimulation they yield is only an exaggerated version of a calmer, steadier, and gentler goading of the human by our vegetal others.


[i] Lin Zhang et al., “Exogenous Plant MIR168a Specifically Targets Mammalian LDLRAP1: Evidence of Cross-Kingdom Regulation by micro-RNA,” Cell Research, 22 2012, pp. 107-126.

[ii] Karen Hardy et al., “The Importance of Dietary Carbohydrate in Human Evolution,” The Quarterly Review of Biology, 90(3), September 2015, pp. 251-268.

[iii] On the subject, he is reported to have said: “I prefer a short life with width to a narrow one with length.” [Quoted in Aisha Khan, Avicenna (Ibn Sina): Muslim Physician And Philosopher of the Eleventh Century (New York: The Rosen Publishing Group, 2006), p. 85.]

What Is Plant Behavior?

Photograph by Peter Shanks.


 Michael Marder

November 2, 2015

Behavior is considered to be the hallmark of an active, purposive attitude to the environment. As we observe animals, we perceive the external signs of behavior in the movements of muscles that allow them, for example, to flee from a dangerous situation or to procure nourishment, achieving easily recognizable objectives. Conversely, connected to the stereotypical view that plants do not move is the idea that they do not behave. The limbs of a tree simply sway in the wind; they cannot, unlike a rabbit’s paws, recoil from a saw or a knife wielded against them. Modifying Aristotle’s dictum that “plants seem to live without sharing in locomotion or perception” in De Anima (410b, 23-4), a vast majority of people today believe that plants live without behaving.

The absurdity of denying behavior to plants is, nonetheless, glaring. Like everything that lives, plants need to nourish themselves, and this operation is far from effortless. It is not enough to expose the leaves to sunlight in an arbitrary arrangement; exposure has to be maximized, especially if other (taller) specimens cast shadow, as they do in a forest or in a jungle. It is a wasteful energetic investment to grow roots in any direction whatsoever; root growth needs to be optimized to reach the most promising patches of soil, with plentiful water and mineral resources.

I am bracketing, in this context, the exceptions of Venus flytrap and Mimosa pudica, two plant species that exhibit the rapid movements of shutting the lobes to capture an insect or of closing the leaves in a defensive response to tactile stimulation. More interesting, to my mind, is the claim that all plants behave in certain ways, regardless of the species they belong to. So, if growth is a kind of slow movement—which is the insight of the very thinker who described vegetal life in strikingly impoverished terms, namely Aristotle—then the fine-grained details of their growth constitute criteria for behavior. From the placement of new shoots and leaves, we may infer carefully made decisions on the most advantageous location for these new parts of plants, grounded on the complex spatial maps they construct.[i]  The pattern of root growth, in turn, is a behavior influenced by the “tactile environment of the root.”[ii] Once we account for differences in time-scales and the experiences of time between the human observer and the observed plant, growth begins to exhibit unmistakable behavioral characteristics that are so obvious in the case of animals.

Richard Karban, Professor in the Department of Entomology and Nematology at the University of California, Davis, defines plant behavior as “morphological or physiological responses to events, relative to the lifetime of an individual”.[iii] In the formulation “morphological and physiological responses,” we should hear another echo of Aristotle, who saw in metamorphosis (literally, change of shape) yet another kind of movement. That is to say: plants behave by initiating a chain of alterations, sometimes at the level of genetic transcription, that permit them to respond to events such as the onset of drought more effectively, seeing that they cannot leave the places wherein they grow. Responding to abiotic, environmental stress, plants can alter metabolic rates, roll their leaves, close stoma, and so forth.[iv]

Of the four types of movement, identified by Aristotle, the only one remaining is decay. Could it be the case that plants also behave by decaying? Clearly, the roots of a tree receive nutrients from the rotting leaves and fruit that have fallen on the ground above them. But a collapsed tree as a whole also becomes the site for a community of fungi, microbes, and insects who decompose it, enriching the soil. Most likely, Aristotle imputed a modicum of agency to decomposition, which is why he included decay in the fourfold concept of movement. Rather than make a laughing stock of his insight, we should interpret it obliquely, in light of what happens when the effects of human behavior impede vegetal decay. Surprisingly, the forests surrounding the Chernobyl reactor site are not decaying as they should, with tree trunks and leaves accumulating over the nearly thirty-year period since the disaster.[v] (This summer’s severe wildfires in the so-called exclusion zone have resulted from this failure of plant decay.) Having interfered with the time-scale of finite life through the use of nuclear power, the byproducts of which are virtually indestructible, human behavior has smuggled an absolute non-adaptation to the environment in the guise of the most versatile adaptation to any conditions whatsoever. It has disrupted the communities of decomposition that are indispensable to soil renewal and to the continuation of life.

Given multifaceted plant behaviors, our task is not to reject behaviorism for its simplistic view of the bio-psychological subject, oblivious to the inner world of emotions, intentions, and desires, but to show that this view is not behaviorist enough. The stimulus-response model it subscribes to works with a very limited time-range proper to a very limited group of organismic changes, which are taken to be synonymous with behavior in general. The friction between depth psychology (including, of course, psychoanalysis) and behaviorism is secondary to the immense richness of behavior, uncoupled from the standards of either an individual species or a biological kingdom. Factoring growth, metamorphosis, and perhaps decay into its semantic range, we will approximate the framework for the term behavior, appropriate to life in all its anonymity and singular universality.

[i] Anthony Trewavas, “Aspects of Plant intelligence: an answer to Firn.” Annals of Botany 93 (4), 2004, pp. 353–57. doi:10.1093/aob/mch059.

[ii] J.L. Mullen, et al. “Root-growth behavior of the Arabidopsis mutant rgr1. Roles of gravitropism and circumnutation in the waving/coiling phenomenon.” Plant Physiology 118(4), 1998, pp. 1139-45.

[iii] Richard Karban, “Plant Behavior and Communication.” Ecology Letters 11(7), 2008, pp. 727-739.

[iv] Cf. Loredana Ciarmiello, et al. “Plant Genes for Abiotic Stress,” in Abiotic Stress in Plants—Mechanisms and Adaptations,” edited by Arun Shanker and B. Venkateswarlu (Rijeka: InTech, 2011).