# Plant Sentience > People involved in the animal movement argue that we should refrain from eating meat either because animals, too, have rights (rights view) or because animals, too, feel pain (consequentialism). Then what about plants? Do plants feel pain too? If plants feel pain, should we refrain even from vegetarianism? People involved in the animal movement argue that we should refrain from eating meat either because animals, too, have rights ([rights view](https://wiki.g15e.com/en/pages/Rights%20view.txt)) or because animals, too, feel pain (). Then what about plants? Do plants feel pain too? If plants feel pain, should we refrain even from ? ## Responses to stimuli vs. conscious experience of nociception Because plants are living things too, they show various responses to external stimuli. Some responses are even very intelligent. But a response to a stimulus does not by itself mean a conscious experience of nociception. To examine what rights another being has, or what interests of another being ought to be considered, we need to distinguish these two. What matters is thinking about whether the latter (conscious experience of nociception), not the former (response to stimuli), exists. ### Plants' terrible screams? According to [one study](https://www.biorxiv.org/content/10.1101/507590v4.full), some plants emit ultrasound depending on the situation. This ultrasound can apparently be detected from some distance away, and there are said to be distinguishable differences in pattern depending on the type of stimulus. A sound wave is a vibration of air; when that vibration falls within the human audible frequency range, we call it "sound," and when it falls outside the audible range, we call it "ultrasound." The study above says that plants produced vibrations in certain situations, that the resulting vibrations in the air could be detected even several meters away, and that through the patterns of the vibrations it was possible to distinguish what was happening to the plant (drought, damage, etc.). The researchers estimate that the vibrations are produced when bubbles formed inside the xylem (the tissue that draws up water and nutrients) burst. It has not been established whether the ultrasound produced in this way is an [evolutionary adaptation](https://wiki.g15e.com/pages/Evolutionary%20adaptation.txt). If it is an evolutionary adaptation, then it is possible that other insects or animals also evolved to respond to this sound. For instance, if a predatory animal can detect the ultrasound a plant emits when pests are present, then the plant could beneficially use the predator to remove the pests, and the predator could beneficially use the plant to find prey, so it is also possible that a symbiotic relationship evolved. The title of one Korean news article introducing this research is "[It has been discovered that plants, too, let out terrible screams when they feel pain](https://www.dispatch.co.kr/2055279)." Expressions like "pain" and "terrible screams," which were never mentioned in the original research, are being used without basis. This stands in contrast to how, when it rains, we hear the sound of rain, but no one says, "Raindrops let out terrible screams as they plummet." ### Plants: "It's dangerous!" ... creating pain signals? [Another study](https://news.wisc.edu/blazes-of-light-reveal-how-plants-signal-danger-long-distances/) introduces the process by which, when a leaf is damaged by a caterpillar and the like, the plant sends a danger signal and activates defense mechanisms. Since plants are living things too and evolved in ways that improve reproductive success, it is only natural that they have various defense mechanisms against danger. But that does not mean they consciously experience danger and feel nociception. In other words, an adaptive response to a stimulus does not immediately imply a conscious experience of nociception. However, the title of one Korean article introducing this study is "[Under caterpillar attack, 'It's dangerous!' ... Plants create pain signals and transmit them from leaf to leaf](https://biz.chosun.com/site/data/html_dir/2018/09/20/2018092000159.html)." Of course, the original study says nothing at all about pain. ### A plant that "sees" and copies the shape of nearby leaves One plant species () can mimic the leaf shapes of other nearby plants. Hypotheses had been proposed that it responds to volatile chemicals from the host plant, or that occurs from the host, but a <2022> study showed that it also mimics the leaf shapes of fake plants made of , thereby rejecting the previous hypotheses. That study proposed, as an alternative, the hypothesis that the plant uses [ocelli](https://wiki.g15e.com/pages/Ocellus.txt) to "see" and mimic the leaf shapes of nearby plants. (See also: [plant vision](https://wiki.g15e.com/pages/Plant%20vision.txt)) It has long been known that plants respond to light (), but it is surprising that this may have developed with enough sophistication to mimic the leaf shapes of nearby plants. Even so, the mere fact that such a sophisticated evolutionary adaptation exists does not allow us to conclude that plants have conscious visual experiences. ## Can we be sure that plants cannot feel pain? But it is also dangerous to assert that plants absolutely have no , that there is no possibility whatsoever that plants feel pain, and that every response plants show is merely the result of mechanical mechanisms. The <17th-century> philosopher is famous for having carried out cruel animal experiments while claiming that only humans possess souls and that all animals other than humans are nothing more than complex machines. It is even said that he nailed down the limbs of living dogs and dissected them. Of course, unlike animals, plants do not have a , nor do they have the that animals possess. But if we think of cases of various evolutionary adaptations that arose independently in species of different evolutionary lineages—such as bird wings and insect wings ()—there is no necessity that evolution must always use the same solution to solve an adaptive problem. Therefore, one cannot simply conclude that plants must be unable to feel pain just because they lack a or nociceptors. This is all the more so when we consider that even in animals there are many cases where nociceptive signals and the experience of nociception do not correspond one-to-one (see: [somatosensory amplification](https://wiki.g15e.com/pages/Somatic%20amplification.txt)). The blunt assertion that plants cannot move also has an excessively animal-centered aspect. Some plants, such as mimosa or the Venus flytrap, can move quickly; some, such as , even fire pollen sacs at insects (!); and even most plants that appear motionless to us, when recorded on video and played back quickly, can be seen actively exploring their surroundings and behaving so as to secure advantageous positions. Many species of plants also actively exchange signals with nearby plants through microorganisms near their roots. There is also a [study](https://royalsocietypublishing.org/doi/10.1098/rsos.211926) showing that fungi (not plants, but still) exchange complex electrical signals between cells and engage in a kind of communication. We should be careful not to overemphasize the point that plants are unlikely to feel pain and then fall into a way of thinking that seems to deny the very life-like characteristics of plants themselves. Perhaps we too may be committing toward plants the very same error that Descartes committed toward animals in the past. Therefore, a somewhat more cautious approach is needed. There is a need for more systematic research into the conscious experiences of plants. ## Studies on plant consciousness ### The difficulties of consciousness research Pain is a subjective conscious experience. Humans cannot objectively know what sort of conscious experience another being has. In , this is called the . Humans cannot know not only whether plants feel pain, but also whether other humans feel pain. We merely infer from outwardly visible behaviors that the other party is likely feeling pain. Whether another being has conscious experiences identical or similar to mine is one of those subjects that science can never settle. Because of these limitations, the best we can do in trying to determine whether plants feel pain is "inference by analogy" and "inference to the best explanation." Inference by analogy takes the form: "I have such-and-such observable features and I feel pain. The other party also has such-and-such observable features like mine, so they probably feel pain too." The more of these "such-and-such features" are shared between me and the other, the more valid the inference becomes. Inference to the best explanation takes the form: "The other party behaves in such-and-such ways under such-and-such circumstances. Among the various hypotheses that can explain this phenomenon, the best hypothesis is that the other party feels pain." Other things being equal, a hypothesis with greater economy (the hypothesis that can describe the phenomenon best with the simplest explanation) is a good hypothesis. This is commonly called . If we take inference by analogy and inference to the best explanation into account, then with respect to the various traits that might be regarded as related to pain or conscious experience, we need to examine what similarities or differences there are between humans, or organisms evolutionarily close to humans, and plants. If similar phenomena are observed across many features, that strengthens the view that plants also feel pain. Conversely, if similar phenomena are observed in almost none of those features, then we should regard the possibility that plants feel pain as low. ### Empirical research: comparing plants and chickens There is a study comparing traits related to across a total of 18 species, including , some , and various . It examines a total of 53 traits across eight categories: responses to noxious stimuli, motivational trade-offs, learning-related indicators, cognitive sophistication, responses to drugs, navigation skills, behaviors related to affective states, and anatomical/evolutionary traits. (See: [sentience in invertebrates](https://wiki.g15e.com/en/pages/Invertebrate%20sentience.txt)) For reference, this study distinguishes between "nociception in the broad sense" and "nociception in the strict sense." In the case of plants, regarding the possibility that they experience nociception in the broad sense, the judgment is "lean yes," while regarding the possibility that they experience nociception in the strict sense, the judgment is "likely no." The reason broad-sense nociception is "lean yes" is that plants too can show various responses depending on external stimuli (). Some researchers ( and others) interpret this as meaning that plants can feel, but most researchers are negative toward this view. Because of epistemological constraints (), we may never know a firm answer even in the future, but according to the study above, the possibility that plants have a conscious experience of pain is extremely low. That study, of course, also has limitations. According to it, for almost all traits related to conscious experience, plants either show no response or nothing is known; but this seems largely due to the lack of relevant research. For example, there are still no scholars researching things like whether plants "engage in play behavior" or "pass the mirror test." ### Pseudoscientific claims If you go to a bookstore, you sometimes see books making claims like, "When we played classical music to plants, they grew better," or "When we spoke kindly to water, the properties of the water changed." Some books are even advertised as if they had tremendous scientific backing. But in reality there is little scientific basis for them. Of course, as discussed earlier, plants are living things too, so they respond in various ways to external stimuli. But a response to an external stimulus does not mean a conscious experience of pain. ## If plants feel pain, does that eliminate the reason to avoid meat? As we have seen, the possibility that plants feel pain is very low. But what if plants do feel pain? If both plants and animals feel pain, does that mean there is no longer any reason, on ethical grounds, to refrain from eating meat? No. That is because, compared with animals eating plants and then humans eating those animals, humans eating plants directly can greatly reduce plant consumption, and therefore plant suffering. If you believe that plants feel pain and are sincerely concerned about that pain, you should still reduce meat consumption (for a comparison of the energy efficiency of vegetarian and meat-based diets, see [the efficiency of plant-based diets](https://wiki.g15e.com/en/pages/Efficiency%20of%20plant-based%20diet.txt)). Vegetarianism is even good for health. On this, see [Colin Campbell](https://wiki.g15e.com/pages/Colin%20Campbell.txt)'s book [What Shall We Eat?](https://wiki.g15e.com/pages/The%20China%20study%20(book.txt)).