The biologist Jordi Casamitjana discusses the ultimate vegan answer to the vegan sceptic remark “Plants Feel Pain Too”, but looking at it from an unexpected approach

I am excited about this one.

I have already written several articles about the “ultimate vegan answer” to several common remarks vegan wisecracking sceptics, reluctant pre-vegans, and assorted carnists say during conversations — often of a vegan outreach nature — where they question veganism and challenge the beliefs of vegans like myself. I have written about the remarks “Where you get your protein from”, “Canines, though”, “It’s the circle of life”, and “I could never go vegan”. In all these articles I deconstructed what I think they mean with such remarks, I compiled the best responses to them, I collected some facts, and I finally synthesised a more sophisticated reply from all this analysis that could be classed as the “ultimate vegan answer” for being more comprehensive, definitive, and undefeatable. I created those answers to enrich both philosophically and scientifically the knowledge base of vegans defending veganism and to give vegan outreachers more “ammunition” if they want to dig deeper into these subjects. However, in all these cases, although I may have offered new angles or perspectives to look at these issues, I did not really create any new “argument” that most vegans would not have used before or take a controversial approach that not all vegans would agree with. I suspect, though, that this one would be different — and I kind of like that.

I am going to tackle a remark that, on the face of it, should be very straightforward to reply to, and you would expect most vegans would easily know what to say when hearing it as they would be able to guess why the remark was made in the first place. A comment that, more often than not, is difficult to take seriously, but I would argue that is the one we, vegans, probably should take more seriously than any of the other “classics”. An assertion that, although it can always be responded to, there may be situations where it would be better not to put down with an absolute denial. I am talking about the statement “Plants feel pain too”.

As with the case of the “Canines” and “The Circle of Life” articles, I would put on my biologist hat to address this one, because I want to look at it from a slightly different perspective. One which some may outright dismiss if they did not know about my qualifications (I am a zoologist, not a botanist, but my five-year degree included a three-year degree in biology, which had botany and plant physiology as two of its subjects). I want to give it an interesting biological twist that will go beyond defending veganism into something more enriching. Something that, I would say, may even form part of the future evolution of veganism itself. 

Read on and you’ll see what I mean.    

Plants Are Not Sentient Beings

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The most common response vegans give to the remark “plants feel pain too” is to say, “No, they don’t, because they are not sentient beings”. If there is no room to elaborate more, this could be a good enough answer, but it is not one I like to give for several reasons. One reason is that denying sentience to others is something that carnism has indoctrinated us to do, and chicken eaters, pescatarians, and even ostrovegans (those people whom bivalves, such as oysters and mussels, are the only animals they eat) often do when they justify who they consume. I am not comfortable asserting that a group of living beings is not sentient, even if they are unlikely to be, because this is such a common carnist narrative — which is opposite to the vegan narrative that takes a precautionary approach and grants sentience to all animals, even if there has not been scientific research confirming sentients for every species of animal. 

I am quite comfortable asserting that all animals are sentient (including insects and bivalves), but this is not the same as asserting that all non-animals are not. The second main axiom of the philosophy of veganism is THE AXIOM OF ANIMAL SENTIENCE, which says “All members of the Animal Kingdom should be considered sentient beings”. This is what all ethical vegans believe, including for animal species yet to be discovered. However, this is not the same as denying the sentience of others, as this axiom could be believed regardless of whether vegans think plants or fungi may or may not be sentient too.

Another reason I do not use this response is that, as an ethologist, I have often criticised scientists who claim they know what non-human animals feel or do not feel, and who assume that if they do not tell us that they feel pain, then they don’t feel it. I have always said that the correct approach is the opposite, assume sentience first and then try to prove an organism is not sentient, not the other way around. In other words, the remark “X does not feel pain because X is not sentient” is a very carnist thing to say, and I am wondering if, as we, vegans, who often still carry carnist relics with us because this indoctrination is difficult to shake off, could be using this response because it comes from such indoctrination (a kind of blind spot we haven’t noticed yet).

The only way to be sure that we are not letting our carnist past dictate this response from the depth of our mind is to check if, indeed, plants are sentient (because if they are not, many would say that they would not feel pain). Let’s start by looking at what sentience is. In my book “Ethical Vegan”, this is what I write about it:  

“At its most basic meaning, sentience is the ability to experience positive and negative sensations, which requires two things: firstly, senses to perceive the sensations from stimuli coming from the environment, and, secondly, a nervous system to process such sensations and translate them into experiences which allow the animals to react accordingly, depending on whether they are negative or positive (i.e. fleeing from an adverse environment or moving towards a source of food or a mate). All members of the animal kingdom can do that. They all have senses to perceive their environment, they all have nervous systems (central or otherwise) to process perceptions, and they all can react according to the type of experience. We are yet to discover any living being not belonging to the animal kingdom capable of doing all of that (although there may be borderline cases where some plants have some movement when touched, such as the Latin American Mimosa pudica, although we are unable to ascertain if the experience is negative or positive due to the lack of an actual nervous system).”

Ah, Mimosa pudica (the touch-me-not plant), a plant that could be a borderline case of sentience (I wonder how many more are there?). What makes this plant borderline rather than fully sentient? Well, I already mentioned the reason: the lack of a nervous system. You may have senses that give you sensations, but if you cannot process such sensations with a nervous system you cannot transform them into experiences — and without experiences, there is no sentience. We have not found any nervous system in any plant yet. We have found respiratory systems, circulatory systems, skeletal systems, and reproductive systems, but not nervous systems (or an equivalent). This means that it is unlikely that any plant is sentient, as despite we have not discovered all plants yet so far we have discovered many and none have a nervous system that would allow them to be sentient.

However, we have assumed that no sentience means no feeling of pain, but this may be a false assumption. No sentience may indeed mean no negative experience of pain, but what about primitive pseudo-senses that cause something akin to pain sensations that will not lead to a negative experience? Is it possible that evolution has started producing “pain receptors” first, before creating the experience of pain? Evolution “creates” biological traits gradually, not all at once, so I think it is possible. I think it is possible that plants like Mimosa pudica, which quickly close its leaves to protect them when touched (and I can confirm they do that as I saw them doing it when I found them during my trips to the Amazon), have simple “sensorial” organs that perceive very basic information from the environment and, without an actual nervous system, create a “behavioural” response analogous to how animals react when feeling pain. 

In such borderline cases, there may be “pseudo-pain” felt (not actual pain as pain receptors are specific organs all animals possess but plants don’t) that causes a reaction that leads to a movement, but this would not equate to an experience, as an experience can be multimodal (it can be positive, neutral, or negative), so it requires computational power that the neurons of a nervous system provide. There are no neurons in the Mimosas, and when the leaves “feel” the touch, there is only one response (close the leaves up). Animals, on the other hand, stay, move closer, or move far away from environments according to whether their experience is neutral, positive or negative — most plants cannot move that way, they can grow into better spaces, but growing is not the same as moving — and animals responses could be nuanced, moving slower or faster depending on the intensity of the experience (plants cannot un-grow, but animals can always go back to places they left if things change).   

So, if there are indeed borderline cases of non-sentient living organisms that could feel something similar to pseudo-pain, then the over-generalised response “Plants don’t feel pain because they are not sentient beings” may be less correct than the response “Some rare plants may have something equivalent to ‘feeling pseudo-pain’ but these are unlikely to have the negative experience of pain as they are not sentient beings”.

Can Plants Communicate?

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A nervous system can be used for many more things than just processing pain and stimuli to react appropriately to the environment. It can also be used to communicate information between organs in an organism or between organisms. We have said that plants do not have a nervous system so you would not expect that they would be able to communicate, right? Well, several studies have suggested otherwise.

Scientists have discovered that several plants emit volatile organic compounds (VOCs) into the atmosphere upon mechanical damage (like an herbivore animal eating the plant) or insect attacks, and other plants can read such compounds and react accordingly (applying a defence mechanism against the cause of such “alarm calls”). That is communication. 

A recent study found an ingenious way to visualise how that happens. Professor Masatsugu Toyota from Saitama University, Japan, and his team achieved such visualisation in real-time by using fluorescence in the mustard plant Arabidopsis thaliana to study what is known as Calcium signalling. This type of signalling is something that also happens in neurons, and involves calcium molecules stored in organelles inside cells which repetitively release and then reaccumulate Ca2+ ions in response to specific cellular events. In the study, after exposure to VOCs emitted from the insect-damaged plants, the neighbouring plants, which had been genetically modified to create fluorescent protein sensors for intracellular Ca2+, showed fluorescence changes (detectable light) indicating an increase in Ca2+ concentration. In other words, when the insects eat one plant, the plant’s fluorescence increases, and soon after the neighbouring plants that are only in contact with the first one by air also show more fluorescence. The researchers also identified which specific cells exhibited the Ca2+ signals 

This phenomenon of airborne communication among plants through VOCs was first documented in 1983 and has since been observed in more than 30 different plant species. The first ever experiment to prove this was done when ecologists placed hundreds of caterpillars and webworms on the branches of willow and alder trees and found the attacked trees began producing chemicals that made their leaves unappetizing and indigestible to deter insects. However, most interestingly, healthy trees of the same species 40 meters away also put up the same chemical defences to prepare against an insect invasion even if they had no root connections to the damaged trees, suggesting that this type of communication is far more efficient than initially thought. In some cases, it is believed that the VOCs also attract predators of the insects that made the plant release them in the first place, so we are seeing here plants warning other plants but also “calling” some animals for help.

If you think about it, this makes sense. This type of communication would be very adaptative and affect survival and reproduction, so you would expect that evolution had favoured this in all types of organisms, not just animals, and plants have been on this planet longer than most animal species (so enough time for evolution to create this). However, this does not mean that plants have a hidden nervous system we have not discovered yet, only that nervous systems are not the only way evolution has created for biological communication. Plants could “talk” among themselves and not be sentient, because you can pass simple information without the need to experience something negative or positive about it. In fact, it should be easier to evolve communication without sentience, as this would require fewer elements and fewer complex structures, so we should not be surprised we find such communication in plants.

It’s kind of typical human supremacist arrogance to assume that communication can only be done by producing words from concepts cooked in a complex brain. Communication happens in Nature in many other much simpler (and more efficient) ways, and it was happening before any human had evolved into existence (that’s why plants germinate at the same time or some trees lose their leaves in autumn). Therefore, plants can indeed communicate between different parts of their bodies and between individuals, and some can even have “sensations” equivalent to “pseudo-pain”, but they can do all that without being sentient, and without having negative experiences.

If non-sentient living beings may feel “something” and can communicate with others, should we not treat them differently than objects? Yes, I agree. I do not think they should be treated as we treat rocks, cars, or coins. They are indeed living organisms, and that, for me, commands some respect, but they are also ancient natural organisms who evolved on this planet and belong to it, and who often help us to live healthy lives, so we should be grateful to them and be extra respectful. I, personally, do not like to harm any plant, and with this, I mean not killing it, cutting parts of it increasing the chance that it would get infected, or even making it “feel” any “pseudo-pain” (for those plants who may have evolved this). That is why I do not tend to use the reply “They don’t feel pain because they are not sentient beings” as I find it a bit disrespectful to plants, and I find it a bit supremacist (in this case, sentient supremacy). Sentient beings are not the only beings I like to respect.  

Can We Still Be Vegan If Plants Evolve Sentience?

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When vegan sceptics say “Plants feel pain too” you know they don’t believe it. No person stopped eating plants believing they were sentient but continued eating animals believing they were not. They say this remark to try to catch us in a contradiction. They are trying to say that if we care that much about not hurting animals, we should stop eating plants because they “also feel pain like animals.” They are not serious, but they are trying to “kill our arguments” for veganism with a spurious caricatured argument to deflect our attention away from what we were going to say. 

I have witnessed some vegan outreaches trying to catch their bluff with responses along the lines of “If you care that much about the plants you should become vegan because most plants grown in agriculture are grown to feed the animals of animal agriculture.” Although this argument is true and this is a good enough answer, I do not use it because I find it “circumstantial”. I do not find it a very good argument because this is only true now, as in the future, when the population of vegans will grow considerably and bans are enacted to prohibit feeding farm animals crops humans can eat, then this fact may no longer be true.

Instead, I prefer to use their statement as a platform to show “how” vegans care about what they care about. I would say something like, “If science proved that all plants feel pain I would definitively do my best to stop harming them, but so far this possibility has only been suggested for some plants, none of which vegans eat.” This may lead to having a conversation about the Mimosa plant and sentience in general in the line of previous chapters, but I think is more interesting to show how much a vegan like me cares about plants (which would have the effect of neutralizing their argument aiming to expose that we do not care about them).

As I said earlier, I try to respect plants and not “hurt” them, but is this something only I do? No, there many vegans I know that do the same, and, if you are a vegan, minimizing harm to plants is an easier goal to achieve than you may think. How? Well, as our anatomy and evolutionary history tell us, we, humans, are essentially frugivore animals (which means we are biologically adapted to eat fruits) who moved out from the trees into the savannah and began eating more starchy plants such as grains, roots, and tubers (we also ate meat, but that never led to any significant physiological change to our frugivore adaptation, while eating starchy vegetables did — humans can digest them better than our closest relatives the chimps and bonobos). And frugivore animals are animals who plants “like” because they help them to spread their seeds. Plants grow succulent and appealing fruits to attract frugivores, so picking them up and eating them is something that does not hurt the plant (on the contrary). 

In the case of grains, these are seeds and fruits that the grasses also need spreading, so when humans do that instead of wind, and the plant has already dried up and is going to whither anyway, there is no harm done either. Even taking some tubers or roots but leaving others in the plant could be done without killing the plant (although industrialised agriculture may be too careless for that). Contrary to leaf-eating animals such as many insects and ruminants, frugivore species like us would not necessarily be threats to plants and instead the plant may want to have them around (and hence they produce so many appetising colours, tastes and smells). Like oak trees would not “see” squirrels as threats and would give them a home and many more acorns than they need to just reproduce, many plants vegans eat could also “regard” humans as “benign” if they are harvested in a natural and holistic respectful way (not like standard modern mechanised agriculture does, though).    

Like me, many people in the past understood this positive mutualistic relationship with plants, and many vegans manifested it in their veganism. In fact, there is a type of vegan (mostly aspirational than real) that exemplifies this: Ethical Fruitarian. This is a type of fruitarian who tries to minimise the harm done to plants for ethical reasons. In my book Ethical Vegan this is what I say about fruitarians: 

A fruitarian is a vegan who mainly eats fruits and avoids roots, tubers, stems and leaves. In this context, the term ‘fruit’ means any botanical fruit (the seed-bearing structure in flowering plants), therefore including some vegetables which are technically fruits (i.e. courgettes, bell peppers, tomatoes, bean pods, etc.). The term ‘fruitarian’ had already been used from the end of the 19th century as synonymous with what we call today ‘vegan’ (but linked to the Christian belief of returning to the ‘utopian’ past of Eden), and in the US is today often used as synonymous with ‘raw vegan’. Fruitarians have not agreed on the exact definition of fruitarianism. Some fruitarians don’t eat nuts, while some eat nuts as well as seeds. It is reported others will eat only what would fall naturally from a plant, and the plant is harvested without killing it or harming it (although some fruitarians say it is a myth that anyone does this).”

Although I eat a Whole Food Plant Based diet with little processed food, I am not a fruitarian as I am not sure whether eating a 100% fruitarian diet is healthy enough, but I definitively like the idea of “ethical fruitarianism”, and in the future, if a fruitarian diet perhaps supplemented with food produced from precision fermentation with bacteria, algae, and fungi is properly developed and proven healthy by the physicians and scientists who I trust, I may want to give it a go (using this type of fermentation would be within the ethical fruitarianism ethos as the fungi and algae used are unicellular species, like bacteria). 

We know people who tried it. Interestingly enough, a very little-known society named the Fruitarian Society was created in England in 1902 by Dr Josiah Oldfield, well before the Vegan Society was created in 1944, and one of its members, Dugald Semple, became the chairman of the Vegan Society three years after its foundation (which meant that fruitarians kind of merged with the rest of vegans). There have been people who tried fruitarianism since (although not necessarily for ethical reasons). Steve Jobs, founder of Apple Inc., and even Mahatma Gandhi, tried a fruitarian diet for a while, and the nuns of the Order of St Elizabeth of Hungary, founded in South London in 1916, are said to follow a fruitarian diet as well. 

Even if in the past fruitarians may have been more aspirational than practical, and even if you think that there is no way that any plant alive today is close to becoming sentient, plants, like animals, are still evolving, so in the future sentience may end up appearing in other kingdoms other than the Animal Kingdom. If that is the case, don’t worry, as we can still be vegans and have a healthy diet and we can do all that by avoiding the sentient plants. We can do that either because we can avoid consuming borderline possible sentient plants that evolved, we would focus more on eating the parts of the plants they “want” us to eat, we can eat produce from veganic farming which takes extra care about the harvesting methods, or we can avoid plants altogether and choose precision fermentation with micro-organisms). 

Perhaps now it is difficult to do most of this, but in the future, it should be easier, so if ethical fruitarians (as opposed to health fruitarians who are a type of raw vegans) may be just aspirational today, perhaps in the future they may become the norm. As the main axiom of the vegan philosophy is the AXION OF AHIMSA that says “Trying not to harm anyone is the moral baseline”, perhaps in the future this will be extended further beyond sentient beings, and future vegans will make more effort than current vegans in avoiding harming plants and the environment — I am working on that myself, so that’s why I am also an eco-vegan. Even the — likely vegetarian — 19th-century writer H.G. Wells described the Eloi, the human inhabitants of the future in his famous novel The Time Machine, as a fruitarian civilization (and he may have got that one right). 

What is the Ultimate Vegan Answer to the Pain in Plants Statement?

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Caring about others, sentient or not, big or small, simple or complex, organismal or ecosystemic, is a virtue that we should encourage, so if we are having a conversation with someone who tells us “plants feel pain too”, this is a good opportunity to talk about the importance of caring. Therefore, here is the ultimate vegan answer I like to give to this remark:

“If science proved that all plants feel pain, I would definitively do my best to stop harming them, but so far this possibility has only been suggested for some plants, none of which vegans eat.  Some rare plants may have something equivalent to ‘feeling pseudo-pain’, but these are unlikely to have the negative experience of pain as they are not sentient beings. But just in case, we vegans would avoid eating those. 

However, all plants are living beings and many form part of nature, so we want to respect them too as far as it is practicable and possible. This is not that difficult for vegans as we eat mostly fruits, seeds, and grains that, if harvested properly, would not harm the plants. On the contrary, plants have evolved juicy, sweet, and nicely smelling fruits to make frugivore species eat them, and in doing so help to spread their seeds, and as we humans are mostly frugivore species we are well equipped to do that too. 

We vegans care about others, and we will try to avoid harming anyone who can be harmed. In the modern world we live in, we may not always be successful in avoiding such harm, but we try to the best of our abilities, and perhaps this is what sets us apart from non-vegans, who may not even try.

Caring about others, no matter the species is something everyone should do, and doing our best not to harm anyone is the vegan way. If it’s true that plants feel pain, I would care about them. If it is not true, I would also care about them. If I grow them or eat them, I will try not to kill them or harm them, or any sentient being around them.”

Caring about others no matter who they are is good, and this is a great message to convey.

Let’s spread it. 

“Originally from Catalonia, but resident in the UK for several decades, Jordi is a vegan zoologist and author, who has been involved in different aspects of animal protection for many years. In addition to scientific research, he has worked mostly as an undercover investigator, animal welfare consultant, and animal protection campaigner. He has been an ethical vegan since 2002, and in 2020 he secured the legal protection of all ethical vegans in Great Britain from discrimination in a landmark employment tribunal case that was discussed all over the world. He is also the author of the book, ‘Ethical Vegan: a personal and political journey to change the world’.