Plants comprise approximately 82% of all life on earth, but there’s still quite a lot we don’t understand about these living organisms. For example, do plants have feelings? Can they experience fear, joy, or remorse?
Plants do not experience complex emotions in the same way people do. Though they can sense environmental changes, suffer from stress, and respond to perceived threats, plants lack a central nervous system or brain. For this reason, they do not have feelings as we understand them.
This article will explore the evidence supporting the theory that plants have feelings and the counterarguments against this idea. Using this information, we’ll be able to discover whether plants experience emotions.
4 Forms of Evidence Supporting the Idea That Plants Have Feelings
The scientific theory that plants may be sentient and experience emotion dates back to the 1800s, with James Perchard Tupper’s work “An Essay on the Probability of Sensation in Vegetables.”
However, this idea may be far older, as the folklore of countless civilizations often includes some form of sentient plant-like creature. These range from the Japanese Jinmenju (Human-Face Tree) to the European Mandrake.
Still, these are examples of mythological cryptids, not substantiated phenomena. And yet, several studies conducted over the last few decades give credence to the idea that plants experience emotion.
Let’s explore some of the strongest forms of evidence that support this theory:
1. Plants Can Sense and Respond to Changes in Their Environment
Nearly all living organisms exhibit a handful of shared qualities and abilities that differentiate them from non-living things.
While there’s no debate about whether plants are living things, the final characteristic of living things (the ability to respond to stimuli) was once considered absent in most plants.
After all, while carnivorous plants like the Venus flytrap (Dionaea muscipula) can respond to physical stimuli to trap and consume insects, a backyard tomato plant has no such biological mechanism.
However, that doesn’t mean that plants (of all types) can’t sense their surroundings and respond to them. One of the most widespread examples of this ability is plant growth direction.
How Growth Direction and Spacing Indicates Awareness
Most plants won’t grow perfectly straight unless they’re exposed to direct sunlight. Instead, they might lean in a specific direction as they grow. The direction they choose is almost entirely dependent on their exposure to sunlight.
That’s because plants need sunlight to grow and flourish. As a result, they’ll often respond to low-light conditions by seeking light. Because plants cannot uproot themselves and “walk” to a sunnier spot, they must grow toward light sources.
This change in growth direction is indicative of a plant’s ability to sense and respond to its surrounding environment.
You can see this reaction almost in real time with sunflowers. These plants turn their “heads” to follow the sun’s path across the sky.
This video shows a timelapse of this phenomenon:
Plants can also sense and react to each others’ presence, either choosing to give one another space (as seen in some trees that exhibit crown shyness) or using one another to gain a biological upper hand (like vines that grow and leech life from trees).
2. Plants Can Experience and Suffer From Stress
Everyone experiences stress at some point in their lives, and feeling “stressed” is a natural reaction to potential threats. For example, it’s natural to feel stressed when preparing for an important exam, upcoming job interview, or major life change.
However, stress isn’t unique to humans. Animals can feel stressed when they don’t have access to life-sustaining resources (food and water) or when they’re kept in unsuitable environments (like too-small zoo exhibits or crates).
Still, organisms within the animal kingdom (including people) aren’t the only living things that can experience stress. Plants can also get stressed out, and the stressors that trigger this response are very similar to the ones that trigger stress in humans and animals.
Comparing the Human Stress Response and Plant Stress
The human stress response is a complex reaction to stressors. Still, one of the most notable physiological reactions to stress is the body’s release of several notable hormones. For example, your body might release adrenaline, vasopressin, and cortisol when stressed.
These hormones trigger various biological changes that can help us survive perceived challenges. This reaction is an evolved trait that may have originated in the earliest humans, many of whom had to face and overcome constant threats to survive and reproduce.
One of the most prevalent stressors humans encounter is a lack of resources or exposure to unsuitable environments. If you’re dehydrated, overheated, or starving, your body is likely under extreme stress.
Plants react similarly to environmental stressors, releasing a hormone called abscisic acid (ABA) when they’re underwatered, exposed to too much sunlight, or planted in nutrient-poor soils.
Naturally, this hormone doesn’t have the same effect on plants as stress hormones have on humans.
However, ABA can trigger plants to release VOCs, inhibit plant growth, and produce noticeable physical changes like changing leaf colors. Stress is the primary reason why a sickly plant’s leaves turn yellow!
In this way, plants “feel” stress when exposed to threats. However, do plants experience the psychological reactions to stress that we’re familiar with (anxiety, fear, anger)?
While the evidence for this type of emotional feeling in plants is scant, recent studies show that plants can emit ultrasonic noises, particularly when stressed or harmed. These sounds are often likened to “screams” and may indicate that plants do, in fact, have feelings.
3. Some Plants Emit Ultrasonic “Screams” When Threatened
Like other living organisms, plants respond uniquely to sound. One of the most well-known experiments testing the effect of sonic vibration (sound) on plant growth is the one attempted by the Discovery Channel’s MythBusters crew in 2004.
This experiment didn’t fully confirm or deny the theory that sound can increase a plant’s growth rate and overall health, but the results did lean in favor of confirming this idea.
You can check out a breakdown of the experiment here:
Still, while external sound vibration may (or may not) help your plants thrive, plants aren’t only capable of receiving these vibrations. They can also emit them! But plants produce “sound” through ultrasonic waves imperceptible to human ears.
These ultrasonic vibrations are constant, and a low vibration threshold is standard in healthy plants. However, the strength (measured in kilohertz) and rate of these vibrations change when a plant experiences stress or physical damage.
When plants are cut, uprooted, or exposed to stressful conditions, they emit “louder” and more frequent ultrasonic vibrations. Some ecologists and biologists have likened these ultrasonic sound waves to screams.
The primary purpose of this reaction is still unknown, but the fact that plants can respond to sound in unique ways may mean that plants can communicate with one another via ultrasonic cries for help. These vibrations may also serve as warnings to nearby plants.
4. Plants Can Release Volatile Organic Compounds (VOCs) When Harmed
Volatile organic compounds (VOCs) are often considered artificial pollutants, commonly found in manufactured plastics and vinyl. When released into the atmosphere (called off-gassing or outgassing), these compounds can generate ozone, a substance that can negatively impact air quality.
However, VOCs aren’t purely artificial. Several plants release VOCs, including oak trees, poplar trees, and peace lilies.
The precise reasons why these plants emit pollution-causing compounds vary, but some of the most significant triggers include:
- Reproduction (pollen generation)
- Physical damage caused by animals or insects
The VOCs that plants release when harmed or stressed have the power to deter hungry herbivores and poison harmful insects. It’s a unique defense mechanism that differs from purely physical defenses like thorns and spikes.
However, there’s a secondary effect worth mentioning.
These powerful plant-based chemicals can also act as a form of communication among plants, providing a warning to surrounding vegetation that danger is near.
How Plants Use VOCs to Communicate
Do you enjoy the smell of freshly-cut grass? If so, you might be surprised to know that the scent you’re relishing is a complex chemical cocktail made of green leaf volatiles (GLVs).
Most plants can release these chemicals, and they typically do so when they’re damaged. In natural environments (those without humans), GLVs generally repel insects that consume leafy green plants while also attracting insects and animals that consume those plant-eating bugs.
As such, these unique VOCs are a form of communication between plants and their surrounding environment. After all, Merriam-Webster defines communication as “a process by which information is exchanged between individuals through a common system of symbols, signs, or behavior.”
While plants lack written or verbal communication, their ability to release VOCs is similar to an animal’s ability to exude pheromones, which are forms of chemical communication. But plant-based VOCs don’t only affect nearby insects and animals—they can also impact other plants.
So, if you trim the leaves off an indoor plant, other plants nearby might fortify themselves against potential harm, thanks to the communication received by the trimmed plant! For some, this interaction is a sign that plants might be capable of experiencing physical and emotional feelings.
4 Reasons to Believe Plants Don’t Have Feelings
Though some evidence supports the idea that plants have feelings, there is no concrete proof to confirm this theory. Additionally, there are counterarguments to consider, many of which indicate that plants cannot experience complex emotions like humans or animals.
Let’s discuss the most significant of these criticisms:
1. Plants Lack a Central Nervous System
The concept of “feelings” has multiple interpretations.
For example, we could be discussing physical sensations like touch, or we could be discussing psychological sensations such as emotion. Still, both of these types of “feeling” would be impossible to experience without a functional central nervous system.
The central nervous system is a complex series of nerves and nerve endings that spread outward from the spinal cord and brain stem in a web-like pattern, reaching almost every area of the human body.
Areas with large clusters of nerve endings (like the fingertips, genitals, and lips) tend to be more sensitive to physical sensations (including pain) than areas with few nerve endings. So, in terms of physical “feelings” like touch, the central nervous system is crucial.
Plants may be able to produce and send electrical signals, much like the central nervous system found in mammals, but these signals aren’t received or processed by a brain.
Consequently, these signals (called action potentials) cannot trigger the type of physical sensations we’ve come to understand as touch, sight, and sound. While this doesn’t fully rule out the potential that plants may be able to experience some types of physical sensations, they likely don’t experience physical feelings as we experience them.
Because of this difference in sensation perception (and lack of a central nervous system), there’s also an excellent chance that plants don’t experience pain.
2. Plants Don’t Have Pain Receptors
Though most of us would do almost anything to avoid feeling pain, our ability to experience this sensation is often crucial to survival. Without it, we may be unaware of life-threatening injuries or threats.
The ability to experience pain is a self-preservation tool that helps humans, animals, and even fish survive. However, without functional pain receptors (nociceptors), we’d lose our ability to access this tool.
Pain receptors are located along nerve endings throughout the body, making them an integral part of the central nervous system.
These receptors send electrical signals along nerve pathways when exposed to elevated levels of pressure or heat. When these signals reach the brain, they trigger the unpleasant sensation we know as pain.
However, plants don’t have pain receptors. Even if they did, their lack of a central nervous system and brain would make it impossible for pain receptors to communicate the sensation of pain.
No biological mechanism could cause plants to experience this basic physical sensation. Plants not only lack the biological tools required to experience pain (a physical feeling), but they also lack limbic systems, which are crucial to experiencing emotion.
To learn more about how plants differ from humans in terms of registering pain, you can check out my other article: Can Plants Feel Pain? Here’s What Science Says
3. Plants Lack the Biological Tools Required to Experience Basic and Complex Emotion
There’s mounting evidence supporting the idea that plants are capable of experiencing and reacting to stress and danger. However, this doesn’t mean plants can experience grief, jealousy, or embarrassment.
These are complex emotions primarily associated with humans (and animals to a limited extent). They’re the result of cumulative experience, a side-effect of our ability to form long-term memories and learn social cues.
Because plants lack brains and complex social interactions, they’re unable to develop complex emotions—or, at the very least, they don’t exist in the same way they do for humans.
Still, what about basic emotions like fear, joy, or anger?
Understanding the Mechanisms of Basic Emotion
To understand whether plants experience these feelings, we must understand how they arise within ourselves. Fear is one of the most straightforward and instinctual basic emotions, and it’s a great place to start.
When you feel fearful, you’re experiencing a primarily physiological response to a perceived threat. This reaction (often called the fight-or-flight reflex) can cause your heart to beat faster, your hands to sweat, and your mind to race.
This instinctual response may have helped our ancient ancestors survive life-threatening situations.
For example, the fight-or-flight response can briefly reduce pain perception, helping you defeat a foe in battle even after suffering an injury. It can also fill your body with adrenaline, helping you outrun a hungry predator. Hence the term fight-or-flight!
However, the human stress response is a complex process that begins in the brain (specifically the amygdala) and extends throughout the central nervous system. Because plants lack both brains and central nervous systems, they’re likely unable to experience fear.
The same can be said for other basic emotions like joy and anger. These all stem from the amygdala, an essential part of the limbic system. Consequently, organisms without a limbic system (like plants) are likely unable to experience these feelings.
4. It Would Make Meat-Free Diets Ethically Questionable
Though this reason is far less scientific, it’s crucial to consider the ethical ramifications of discovering plants have feelings.
After all, plant-based diets are currently considered an ethical and eco-friendly alternative to carnivorous diets. If botanists and ecologists were able to confirm that plants are capable of experiencing complex emotions, just like us, consuming plants may be considered just as ethically questionable as consuming animals.
Because humans need to eat to survive, this revelation would significantly change our ethical food options. In a future where it’s confirmed plants can feel, the human race may turn to bacteria-based food sources like algae!
Plants can sense their surroundings and respond to stressors in several ways. Evidence supports the idea that some plants can communicate with one another, especially when harmed.
However, plants lack a central nervous system or brain. As a result, they’re incapable of experiencing the types of complex emotions that we associate with sentient life.
If the theory that plants can experience complex emotions is ever confirmed, the ethicality of plant-based diets may be called into question.