Are plants conscious and do they feel pain? | The Economist

Key Concepts

• Plant Sentience/Intelligence: The capacity for plants to process information, solve problems, and respond to environmental stimuli without a central nervous system.
• Bioelectric Fields: The theory that multicellular organisms use electrical voltage patterns across cells to store information and coordinate behavior, independent of neurons.
• Circumnutation: The spiral growth movement of plants (e.g., bean plants) used to locate physical supports.
• Conditioned Learning: The ability of organisms to modify behavior based on past experiences (e.g., Mimosa pudica).
• Adaptive Pain: The evolutionary perspective that pain is a mechanism for mobile creatures to escape harm, which may not be applicable to sessile (stationary) organisms like plants.

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1. Evidence of Plant Intelligence and Sensory Perception

Plants exhibit complex behaviors that suggest they are not merely passive organisms but active problem-solvers.

• Visual Perception: Plants can distinguish between light and shade. Some vines can mimic the leaf shape of the host plant they are climbing.
• Auditory Perception: Plants respond to sound frequencies. They can detect the sound of a caterpillar chewing and release defensive toxins in response. They can also "hear" the sound of water in pipes, directing their roots toward the source.
• Echolocation: It is hypothesized that plants use "circumnutation" (spiral growth) combined with the sound emitted during cell division to reflect sound off objects, allowing them to locate supports like poles before physical contact.

2. The Role of Anesthetics and Consciousness

A significant experiment involves placing plants, such as the Venus flytrap, under anesthesia (e.g., xenon gas).

• The Experiment: When anesthetized, the Venus flytrap fails to close its trap when triggered by a fly.
• Implication: Because these chemicals inhibit consciousness in humans, their effect on plants suggests a parallel state of "being" that is temporarily suspended. While the speaker cautions against using the term "consciousness" (which implies a developed self-awareness), he argues that "sentience" is a more accurate descriptor for this purposeful, responsive state.

3. Memory and Information Storage

The discussion challenges the assumption that neurons are the only medium for memory.

• Case Study: The Mimosa pudica (sensitive plant) closes its leaves when touched. When subjected to repeated, harmless shaking, it eventually stops closing its leaves, demonstrating it has "learned" the stimulus is not a threat. This memory persists for up to 28 days.
• Mechanism: Research by biologist Michael Levan suggests that bioelectric fields—not brains—store information. Using voltage-sensitive dyes, researchers have observed that cells maintain electrical patterns that govern behavior and regeneration. Even when a planarian worm’s head is removed, the body retains learned information, proving memory is stored in the bioelectric field of the body.

4. The Question of Pain and Ethics

The speaker addresses the moral dilemma of whether plants feel pain, noting two conflicting expert perspectives:

• Perspective A: Plants feel pain, but humans must consume them for survival.
• Perspective B (Adaptive Theory): Pain is an evolutionary tool for mobile creatures to escape danger. Since plants are sessile, pain would be non-adaptive and unnecessary.
• Synthesis: The speaker concludes that because many plants have co-evolved to be eaten (e.g., fruits for seed dispersal, grasses for ruminant grazing), the consumption of plants remains ethically sound.

5. Conclusion: Redefining Intelligence

The core argument is that nature creates "problem-solving creatures" to navigate unpredictable environments. Because the environment is too complex to be fully programmed by DNA, life forms—including plants—have evolved the capacity for computation and learning. Neurons are merely one specialized way to achieve this; other biological forms utilize bioelectric fields to perform similar functions. The speaker reaffirms that one can continue to "eat food, not too much, mostly plants" with a clear conscience, as plant intelligence is purposeful and adaptive rather than reflective or self-conscious.