Plants are living beings, just like humans and animals. They breathe, eat, grow, and reproduce. But are plants conscious? Can plants feel pain? Does it hurt plants when we cut them, eat them, or pluck them? The answer may surprise you.
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Scientists Disagree About How Plants Process Pain
Believe it or not, there is no clear cut answer as to whether or not plants feel pain. Because plants do not have a nervous system, they do not experience pain in the same way that humans and animals do.
However, plants do respond to stimulus and some plants have reactions that seemed designed to protect them from harm. They definitely have ways of perceiving the world around them, and in their own way, may feel pain.
The Argument Against Plants Feeling Pain
If you asked a neuroscientist, they would most likely tell you that pain is something the brain creates. Plants do not have a central nervous system, brain, nerves, or pain receptors, so it can be said with confidence that they do not feel pain, at least, not in the same capacity as animals and humans.
Pain in humans and animals can trigger the “fight or flight” response as our bodies attempt to interpret the sensation we’re feeling. Plants can’t exactly fight or flee, so some scientists argue that there is no need for them to feel pain.
The Argument for Plants Feeling Pain
While it’s clear that plants don’t feel pain in the same way that people do, science does show that plants respond to stimulus that would cause pain in humans and animals, like cutting, breaking, or pulling.
These responses can’t be classified as “pain” in the traditional sense of the word, but they do show that plants have more awareness than we may realize.
There is an entire field of study devoted to how plants respond to stimulus, called plant neurobiology. This may seem like a bit of an oxymoron, since plants do not have neurons. But this field of study is legitimate, and has led to many discoveries about how plants respond to the world around them.
The Root Brain Hypothesis
Late in his career, Charles Darwin and his son Francis published the Root Brain Hypothesis. Their theory was that the roots of a plant serve as a sort of brain, interpreting stimuli from the soil and communicating them to the rest of the plant. The Darwins though the behavior of a plant was determined by what happened the cells of the root.
The Darwins’ hypothesis was controversial at the time, but as scientists learn more about plant growth and behavior, it becomes more and more clear that Darwin was ahead of his time.
The Smell of Cutting Grass
If you live in an area where homes have grass lawns, you are no stranger to the smell of grass being cut. But this smell isn’t just a fresh spring odor; it’s a method of communication.
The strong smell of fresh cut grass is actually a distress signal. When cut, grass and other plants release a compound called green leaf volatiles (GLVs). These GLVs in grass create the smell we’re so familiar with, which is intended to send a message to nearby creatures that is being attacked.
What this means is, while plants don’t have a brain, they do have a sort of “language” that they use to communicate their distress to other living things.
Wild Tobacco Plants and Caterpillars
Another interesting example of plants communicating has been found in wild tobacco plants. When tobacco hornworm caterpillars eat the plant, the plant releases GLVs that attract another insect, the Geocoris (also known as the Big-Eyed Bug). The Geocoris feeds on the eggs and larvae of the hornworm caterpillar.
Here’s what Science has to say about the interaction in the study the released on the topic:
[Researchers] found that when these plants are attacked by tobacco hornworm caterpillars, Manduca sexta, the caterpillars’ saliva causes a chemical change in the GLV compounds the plants had produced. These modified compounds then attract predatory “true bugs,” Geocoris, which prey on hornworm eggs and young larvae. Although more research will be needed to figure out exactly how the molecules in the caterpillar saliva cause this change in the GLVs, it’s clear that the caterpillars themselves cause the change in the GLV signal, the researchers say. It may thus be possible someday to induce the same sort of change via genetic engineering, which might protect plants against pests without encouraging the resistance that pests develop in response to pesticides.
Science
27 Aug 2010:
Vol. 329, Issue 5995, pp. 1075-1078
DOI: 10.1126/science.1191634
Arabidopsis Plants and Acoustic Perception
Caterpillars also revealed an interesting discovery in the way that plants process sound. When researchers exposed the Arabidopsis plant (a flowering mustard plant) to recordings of cabbage butterfly caterpillars eating leaves, the plants produced a high amount of mustard oils. Mustard oils are what these plants make to deter insects.
While the Arabidopsis cannot “hear” the sound of the caterpillars chewing, it can feel the vibrations of this sound. Amazingly, the predator doesn’t even have to be present for the plant to respond defensively! The sound alone causes the plant to defend itself from its perceived attacker.
Mimosa Pudica
The Mimonsa pudica is better known as the touch-me-not plant or the sensitive plant, so named because when its leaves are touched, they close and “play dead” as a means of defense.
This response itself shows the plant’s desire to protect itself and avoid “pain.” However, the Mimosa pudica takes its knowledge and understanding of its environment even further.
The Mimosa pudica plants at Kew Gardens in London have been touched by thousands of visitors over the years. As a result, the leaves of these plants no longer close once they sense human touch. The Mimosa pudica have learned, in their own way, that these touches are not a threat to their safety.
This development and the apparent ability of plants to learn from receiving the same stimulus over time continues to challenge how we think about plants and consciousness.
Is it inhumane to eat plants?
If plants possess a type of consciousness that allows them to process sensations and send distress signals when they experience harm, should we feel bad about eating them?
People for the Ethical Treatment of Animals (PETA) claims on their website a plant-based diet will actually cause less plants to be consumed, since so much of the world’s crops go to feeding farm animals. They feel that the vegan diet is the most ethical choice for both animals and plants, and is preferable morally to eating meat.
Diet and the ethics around what to eat are a very personal choice, and are unique to each person. We all have to eat to live, and fruits, vegetables, and other plant life are considered a key part of a healthy diet.
Conclusion
So, do plants feel pain? Yes and no. What’s most important to realize is that we still have much to learn about plants and how they respond to stimulus. Plants may not have brains or nerves, but they perceive much more than you might think.
