Minds Before Brains?

In Chapter 1’s first section, “Minds Before Brains?”, Pollan asks how widespread consciousness is in nature. Western thought has long claimed that subjective personhood (i.e., consciousness) is unique to humans. The idea was first proposed by thinkers like Galileo and Rene Descartes, who both split reality into two parts: the physical and mental. Descartes claimed that humans alone possessed a mind, thus granting himself permission to conduct experiments on animals because they were not conscious beings and therefore could not feel pain.

However, this separation of body and mind made it difficult to study consciousness because it “inadvertently elevated consciousness, unmoored from nature, into something very much like magic” (5). Pollan therefore suggests starting with research on sentience, a simpler form of consciousness, which some scientists believe exists more broadly in nature.

Plants Awaken

In the next section, “Plants Awaken,” Pollan considers plant sentience. He first began to consider the idea of plant consciousness while under the psychedelic influence of psilocybin mushrooms. Several researchers have noted that psychedelic experiences increase a person’s ability or willingness to attribute consciousness to other entities. While some argue that this is merely a form of magical thinking, others suggest that psychedelics help humans move past Western biases to consider other possibilities. Pollan describes such an experience while eating psilocybin mushrooms in his garden and suddenly becoming overwhelmed with the sense that the plants around him had sentience.

After this experience, he began to question the assumed divide between animal and plant life. While scientists and philosophers have recently been willing to grant consciousness to animals, very few consider the possibility for plants. The reason is that animals have nervous systems similar to humans while plants do not. However, recent research indicates that brains are not, in fact, necessary for certain levels of awareness.

Is It Like Anything to Be a Plant?

In “Is It Like Anything to Be a Plant?”, Pollan discusses a famous philosophical essay on the topic of consciousness: “What Is It Like to Be a Bat?” by philosopher Thomas Nagel, published in 1974. Nagel defines consciousness as “what it is like” to be a particular thing, for instance: “if there is ‘something it is like’ to be a bat, or any other being, then that being must have some kind of subjective experience” (9). This is his basis for defining consciousness. His conclusion is that it must be like something to be a bat even if we cannot determine what that is.

Pollan applies this same concept to plants, though it is less supported by scientific consensus. A 2024 conference on consciousness declared that “empirical evidence indicates at least a realistic possibility of conscious experience in all vertebrates […] and many invertebrates” (12) but does not include plants.

A Brief Digression on Terminology

In the fourth section, “A Brief Digression on Terminology,” Pollan discusses various terms used by researchers. Sentience is “the most elemental form of consciousness, a […] precursor to the full-fledged phenomenon” (13), which includes an ability to sense one’s environment and respond to changes within that environment. It implies awareness, preference, and a basic form of agency but lacks a sense of self, emotion, or reasoning. Crucially, “all conscious beings are sentient, but only some sentient beings are conscious” (13), and the two exist on a spectrum without a clear division.

Intelligence is defined as a “fixed goal with variable means of achieving it” (13) which suggests a capacity that goes beyond mere instinct. Consciousness is not required for intelligence. Similarly, cognition, the “acquisition and processing of information” (14), is related to consciousness but is not dependent on it. Cognition and intelligence are capacities to collect, process, and respond to information, while sentience and consciousness require sensation/feeling and a subjective point-of-view.

Enter the Plant Neurobiologists

The mid-point section in Chapter 1 is “Enter the Plant Neurobiologists.” It introduces the ideas of scientists and philosophers who challenge anthropocentric and neurocentric biases. In 2017, plant neurobiologist Paco Calvo published an article in which he suggested science does not yet know enough to conclusively state that plants do not have consciousness. Calvo summarized some key findings in plant neurobiology. These findings include demonstrations that plants can: “learn and form memories,” “predict changes in their environment” and take steps to deal with those changes, “send and receive signals from other plants,” tell the difference between themselves, plants of the same type, and competitor plants in their environments, and integrate information from more than 20 senses (17-18). While this research does not prove that they are conscious, it suggests that plants possess some level of awareness, preference, point-of-view, and agency.

Are Neurons Overrated?

The section “Are Neurons Overrated?”, highlights the work of one of the most vocal plant neurobiologists, Stefano Mancuso. Mancuso’s studies have revealed approximately 3,000 chemicals that plants use to communicate or integrate with their environments. Mancuso performed an experiment in which the root of a corn plant successfully navigated a maze to find nutrient fertilizer. Similar maze experiments with mammals have been cited as proof of their intelligence and should, therefore, count for plants as well.

Intelligence is a basic biological function that allows living beings to solve problems in their environments. Mancuso argues that intelligence can manifest in distributed systems, such as a flock of birds, and not only in neurological systems like brains. He thus suggests that neurons are not necessary for awareness and intelligence.

Mancuso believes that root tips in plants function similar to individual birds in a flock, providing information and responding to it to create collective intelligence. Roots can sense and interpret many kinds of information and “decide” how to respond. Some would argue against assigning words like “decision” and “intention” to plants, but Mancuso disagrees. Pollan, after watching a time-lapse video of a plant growing and exploring its environment, likewise begins to sense a purpose or intent in its movements.

Plants, Conscious and Unconscious

The next section, “Plants, Conscious and Unconscious,” continues this argument. Due to the difficulty of explaining consciousness, Mancuso defines it “by subtraction,” as “something we always have, except when we are sleeping or under anesthesia” (27-8). He posits that if a living thing can be anesthetized, they must be conscious. He has demonstrated that the same chemicals that work on animals likewise anesthetize plants. Though they do not yet understand why, he crucially notes that biologists do not understand precisely why these chemicals work on humans either.

Mancuso thus concludes that plants have two basic states of awareness—offline and online, and that the online state must include some level of consciousness (the idea being that you cannot fall asleep if you were never awake). Pollan, however, pushes against this conclusion by asking what happens when he unplugs a toaster. A toaster does not sense or feeling anything when it is offline versus online. However, he admits, a toaster is not a living being.

Pollan then asks whether plants feel pain, recalling Descartes’ argument that animals did not feel pain because he did not believe they had consciousness (a conclusion that has since been disproven). Some researchers suggest that plants do feel pain. Mancuso, however, is doubtful. He argues that pain is a useful kind of information for survival in animals that can move and escape danger. This kind of information is not useful to plants who cannot pick up their roots and run. There is therefore no reason to conclude that plants evolved to include that sensation in their subjective experience.

Minds Without Neurons

In “Minds Without Neurons,” Calvo and Mancuso both urge Pollan to next speak with developmental biologist Michael Levin. Levin’s research challenges science’s biases toward the neuron and the gene. He argues that every cell in a body can do what a neuron does, simply in different ways or at slower speeds. Likewise, he notes that science’s deduction to genetic structures in DNA stems largely from the fact that DNA survives the death of a cell whereas other forms of information do not. Instead, he suggests that bioelectricity, which dies with the cell’s death, is an organism’s real “software” (34). Bioelectric networks are crucial to the organization of multicellular organisms.

He has demonstrated this by creating a creature he calls a Xenobot: skin cells from a tadpole, placed in a solution with nutrients, and freed from the tadpole’s bioelectric field. Once freed, the skin cells clump together to form a tiny “proto-organism” within which a new bioelectric field emerges. These Xenobots thus demonstrate the way that “purposeful, intelligent behavior” can arise spontaneously in the interaction between cells, suggesting that sentience may emerge in an early stage of evolution.

Levin also argues that intelligence begins with the goal of homeostasis: “an entity’s desire to maintain a certain range of internal conditions necessary to survive” (39). To maintain homeostasis, an organism must be able to sense its environment and take action in response to changes. This, he argues, is basic consciousness. When Pollan points out that a thermostat does this, Levin agrees that “life begins with a thermostat” (39) and increases in complexity from there. Levin calls himself a “gradualist” (38) who is unwilling to draw a hard line between living and machine intelligence.

The Physics of Sentience

In the penultimate section, “The Physics of Sentience,” Pollan asks how science can build a bridge between this basic concept of chemistry and intelligence to larger concepts of the mind. Levin suggests that he speak with Karl Friston, a physicist, neuroscientist, and psychiatrist whose work has been influential for Levin, Calvo, and others. He provided the frameworks behind the computational tools used in brain imaging and the “leading model of perception known as the Bayesian brain” (42), a brain model which posits that perception is less about constructing an image of the world with our senses and more a matter of generating predictions about the world based on prior experience and probability.

From this, Friston developed the “free-energy principle” (43). Friston argues that the challenge of any complex system is to survive entropy—the physics principle that dictates that all matter tends towards disorder. In Friston’s theory, entropy is also called surprise or uncertainty, negative experiences that threaten a system’s survival (he uses the terms entropy, free-energy, surprise, and uncertainty interchangeably). To survive, complex systems need three things: a boundary or membrane that separates inside from outside, a sensory apparatus that can sample the environment outside the boundary and deliver that information to the system inside, and a way to act on that information to resist the forces of entropy.

Therefore, the common goal of living things is to reduce surprise and maintain homeostasis. This is difficult because the boundary necessary for survival simultaneously prevents systems from directly accessing the reality of their environments. Therefore, systems use inference—predictions based on prior experience and probability—to construct an image of the environment as it should be, which sensory apparatuses sample for comparison. Crucially, inference does not require a mind. Like Levin, Friston is a gradualist, and agrees that a thermostat fits his theory of inference and homeostasis.

In fact, all consciousness begins as a kind of thermostat, and each level of consciousness corresponds to rising levels of complexity in one’s environment. The complexity and novelty of human social behavior require human levels of consciousness to evolve, but functions on the same basic principle.

The Hard Problem of Life

In the final section, “The Hard Problem of Life,” Pollan reflects that none of these theories solve the hard problem of consciousness. He adds that the question of consciousness is the same as the question of life. Philosopher Evan Thompson likewise posits that the question of individuality and agency is the same in explanations of life and sentience. And he believes that Western thought’s difficulty with consciousness stems from its “faulty framing” (56). Due to the dualistic split begun by Galileo and Descartes, Western science fails to address subjective experience, which is not merely a field of knowledge but also the only thing by which anything is knowable.

He suspects that sentience is an integral element of life and therefore consciousness cannot be split from the material body. He suggests that Indigenous epistemologies, meditation, and psychedelics may therefore be more useful avenues of research.