Do Plants Feel Pain? A Detailed Analysis

Why is it okay to eat plants and not animals? This may seem like a silly question but it’s not. There are hidden complexities and slithers of truth behind the statement that plants feel pain, but more importantly, this question is the fundamental challenge any carnist will have against vegans and it cuts right down to the bones of our philosophy. Why is it okay to eat one form of life but not another?

If we can’t give a sufficient answer, our activism will likely be ignored, brandished as dogmatic, and may do more harm than good.

There are, of course, simple and obvious answers: “pain”, “sentience”, and my personal favourite, “how about you try killing a carrot and try killing a pig and see what happens?!” However, these answers have complexities that need to be explored, and in doing so I discuss the capacity to suffer, individual rights and an abuse of trust.

Do plants feel pain?

Much has been said about the way plants sense the world and many claim that plants can see, hear, communicate and feel pain[1]. In fact, these claims are all partially true. The Arabidopsis plant has at least eleven different types of photoreceptor (compared to our four)[2] helping them to detect and respond to light. Some can respond to the vibrational waves created by a caterpillar chewing and many plants have forms of communication.

However, a plant has no central nervous system, no specific organ to detect these stimuli and no specific organ to process them either. Plants detect a stimulus and react, biologically, chemically or mechanically, absent of any subjective processing of the information. In this way, plants are more analogous to the computer than they are to humans or other animals. However, this doesn’t necessarily preclude plants from feeling pain.

The International Association for the Study of Pain has defined pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”[3] Pain is a complex mental state and it is notoriously difficult to detect whether or not other animals feel pain, let alone plants, and it cannot be determined unambiguously through observation alone.

However, one thing we do know is that pain is NOT just an extreme form of touch. For pain to be felt, the lifeform must have nociceptors (pain receptors) or nociceptor-like receptors. These are receptors are different from ordinary touch receptors. Indeed, there are genetic malfunctions leading to an absence of nociceptors such that those who experience this can never feel pain, only severe pressure.

The standard way of determining if another animal feels pain is through argument-by-analogy based on certain known pre-conditions and observational response to potentially pain-inducing stimuli. Philosopher Gary Varner has reviewed the scientific literature on pain in animals and has produced the following table[4] :

Note: endogenous opioids are opiate-like substances produced in the body. Two examples would be endorphins and endomorphins, both effective painkillers.

One of the key aspects of an animal’s ability to respond in a similar fashion to humans is the ability to make decisions between stimulus avoidance and other motivational requirements[5]. In humans, this can be seen when an individual refuses to drop a plate that is too hot, ensuring they can put it down safely and not ruin their dinner. To weigh up these decisions, an individual requires some level of subjective processing of the environment and their desires, also known as sentience. (The generally accepted definition of sentience is the ability to experience the environment subjectively. This means that not everyone will process it the same way and an individual may not process the same stimulus in exactly the same way each time).

The general purpose of pain is to ensure the organism can avoid damaging stimuli. It is a survival mechanism. Avoidance learning is a key component to the categorisation of pain in animals. Plants do not have the capability to avoid pain and there are good biological reasons for this. All plants of the same species are genetically identical. It does not matter if one plant dies, so long as others of the same species survive. Weirdly plants do react to analgesics[6] but they lack nociceptors (or nociceptor like receptors), they lack a brain, they lack endogenous opioids and they lack a similar response to humans. Plants cannot experience the world subjectively and any anthropomorphising of a plants ability to detect its environment distorts the biological reality of a plant’s functioning. To quote Daniel Chamovitz[7], author of What a Plant Knows, “you can definitely kill a plant, it just doesn’t care” and this is where they differ greatly from animals.

#NameTheTrait: There is no trait that justifies animal abuse

Sentience provides the capacity to suffer from pain, fear and distress, as well as providing the capacity to feel a sense of wellbeing. Every vertebrate has the capacity to feel pain and reacts in similar ways to humans. Plants, however, may be able to detect damaging stimuli but they cannot suffer.
We grant rights to prohibit actions that cause the pain and suffering of other human beings so why do we not extend these rights to animals that are equally capable of suffering? There is no trait in animals, absent or present, that justifies the infliction of pain and suffering that would also justify the infliction of pain and suffering onto a human were that trait also absent or present in that person. This is known colloquially as the #namethetrait argument[8]. We accept that it is not acceptable to harm humans who aren’t as intelligent us, nor is it acceptable to harm humans who aren’t as well developed as us, and so these arguments can’t be applied to animals. If we believe human beings should be free from actions that inflict pain then so should animals.

A counter-argument is that rights require a responsibility of the individual to uphold the rights of others and that animals are incapable of doing so. Therefore, granting animals rights would be to water down the very concept of rights and remove all responsibility even from those capable. However, this argument falls down in two aspects. Firstly, animals can protect the lives of humans and there are many cases of animals saving the lives of humans[9]. Secondly, and more importantly, we do not deny humans their rights even if they are incapable of protecting the rights of others. We don’t deny rights for children, the incapacitate or those with certain mental conditions, in fact, we often fight for their protection even more. Why don’t we act this way towards the voiceless?

Some people try to justify the infliction of pain and suffering based on the very fact that non-human animals are a different species and that only certain species should be protected. Usually, the species granted protection are found within our “in-group”, cats, dogs and other domesticated animals. Using species itself as the trait that determines moral value is known as speciesism and it operates on exactly the same mechanism as racism. “This species is not worthy of moral protection due to its species” is logically analogous to the statement “this race of people is not worthy of moral protection due to their race”. People once tried to justify their racism based on the different traits of individual races but we now recognise that there is no sufficient distinction, in much the same manner as the #namethetrait argument laid out above. The exact same thing can be said for speciesism. If we are against racism, which I hope we are, then we should also be against the discrimination of all forms of sentient life that feel pain and suffer. Ingroup preference should never be a justification for oppression or the infliction of pain.

Plants don’t feel pain, they detect damage. There is no central nervous system and there is no subjective processing of the stimulus. A plant’s response to its environment is purely objective. Action leads to reaction. Input leads to output. Every single time. This is the fundamental difference between sentient life and non-sentient life. Sentient life processes its environment in a different manner depending on its own genetics, experience and mood. Bees have been shown to exhibit different behaviours depending on different potential emotional states[10]. Emotional responses and changes in behaviour have been found all throughout the animal kingdom. The same cannot be said for plants. With plants, there are only biological, mechanical and chemical responses to stimuli. There is no subjective interpretation of the world. There is no individuality.

Individual rights are the cornerstone of Western civilisation

Individual lives matter, and individual rights should be respected. The sanctity of the individual stems all the way back to the early formations of Christianity and has formed the cornerstone of Western civilisation. The sanctity of the individual paved the way for the end of feudalism, brought about the scientific method, and has put the West at the forefront of human rights[11]. The recognition that each individual life is of importance and value is the greatest thing about western culture. But we have a rather big blind spot when it comes to which individuals matter. We’ve rightly reached the conclusion that every individual person matters, so why don’t we recognise that for other animals?

Part of it will be a lack of exposure to the vast array of personalities and intricacies present in animal behaviour but part of it also comes from a denial of their individuality.

Individuality is created by three things: genetics, experience and sentience. The first two are fairly obvious, people with different genetics and different experiences will act, think and feel differently. However, sentience is an incredibly important factor.

Without the ability to process the world subjectively the individual is just a complex mechanical computing entity. A robot, detecting and responding to stimulus in the same way and processing information uniformly and this is what we find with plants. However, the individuality that comes with sentience is found throughout nature and can even be seen in cow behaviour. Like you and I, cows have complex emotions and personalities and they even have best friends[12]. Again, there are no sufficient reasons not to grant animals the right to life, free from oppression. These animals are individuals, with no sufficient differences to humans, it follows that individual rights should be extended to them. To deny this would be to diminish the very notion of rights. If we can arbitrarily pick and choose which life to grant rights, we make a mockery the very notion. We must have a foundational principle determining which life should be protected and the only morally consistent characteristic is that of sentience.

Not only are we diminishing the rights of the individual but we are also disrespecting the trust these animals have put in us. Throughout history we have operated in cooperative manners way with animals. It is believed that dogs domesticated themselves, recognising the benefits of living around other creatures who held stores of food[13]. The more docile species (and individuals) would approach human settlements and be greeted and petted and would receive food. Eventually, we became fond of them and recognised that they could help us in hunting and protection. But the relationship is more than just transactional. When we pet dogs and cuddle up with them, both individuals experience a release of oxytocin[14], the neurochemical responsible for bonding and commonly known as the “love hormone.” These relationships are reciprocal, and the same can be said for cows, chickens and pigs. However, somewhere along the line, we lost this connection and we refused to hold up our end of the deal. We took these animals in and now we disrespect and renege on the implicit arrangement we once had. These animals trust and care for us and now we continue to unnecessarily and unfairly dishonour that trust.

In summary, we arbitrarily and unfairly cause suffering to beings that can and do feel pain. These animals, much like ourselves, deserve liberty and the right to life. They are individuals with individual personalities and experience the word individually with their own shared emotions. These animals are so incredibly similar to ourselves. There are no sufficient differences that justify our treatment of animals. They have the same emotional responses, the same experience of love and joy but also the same experience of fear and distress.

It is time we focused on all the wonderful similarities that we share and come to recognise all animals as deserving of protection.

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