Jeremy Bentham, an 18th century utilitarian philosopher, famously asked: “The question is not ‘can they reason?’ or ‘can they talk?’ but ‘can they suffer?’” A utilitarian philosopher of our times, Peter Singer, latched into that question to write his book Animal Liberation, and so the modern animal rights movement was born. Basically, Peter Singer and many other animal rights activists claim that animals suffer like humans and therefore they should be treated like humans. Put in a more sophisticated way, Peter Singer argues that the moral imperative of equality dictates “equal consideration of interests”, that is, that the interests of all beings receive the same consideration. Animals have an interest in avoiding pain, therefore egalitarianism demands that we respect that interest. It is argued further that claiming human superiority based on our superior intelligence, our ability to talk or our culture is just stacking the cards in our favor because those are the special attributes of our species. By the same token, an elephant may claim moral superiority based on the fact of having a trunk.

However, the whole argument is based on the claim that animals suffer and, moreover, that they suffer like us. Singer and the other animal rightists just assume that they do. I think this is a faulty assumption that needs to be addressed head-on, but I understand why they take umbrage in it: the whole problem of defining suffering seems intractable at first sight. ‘Suffering’, like ‘happiness’ and ‘consciousness’, belong to a class of concepts that are at the same time abstract and fundamental, so that defining them in terms that are non-circular seems nearly impossible. If you look at dictionary definitions of ‘suffering’ you will find that they refer to pain, unpleasantness or perceptions of threat, which are just synonyms or examples of suffering. This does not represent a problem when the idea of suffering is applied to human beings, because we can get accurate descriptions of their suffering from other people. However, when we want to apply this concept to animals we need a clear idea of what we are talking about, otherwise we risk falling into one of two opposite pitfalls: self-serving callousness -choosing to think that animals do not suffer because this is convenient for us; and anthropomorphizing – thinking an animal suffers just because we would suffer if they did that same thing to us. The latter feels intuitively true because is based on empathy, a very powerful human emotion. However, it is not a rational conclusion.

Just like in the case of happiness and consciousness, the problem of suffering can be studied scientifically. In fact, there are a lot of scientific studies related to suffering because one important thing the public demand from scientists is to find solutions to pain and other forms of distress. Just like in the case of happiness and consciousness, science may not have come up (yet) with a complete description of suffering, but it certainly can tell us a lot of things about it. I think that this information can help us form an educated opinion about whether some particular animal suffers or not.

Most people would agree with the idea that not all living beings suffer. One of the most peculiar things about life is that it seems goal-directed: living beings strive towards keeping themselves alive and making more beings like them. However, this does not imply any form of consciousness or intentionality; it is just something that living beings do automatically because otherwise they wouldn’t be living anymore. It is important to underline this fact because this striving to stay alive can be easily confused with the “interest” that Peter Singer talks about. Yes, life perpetuates itself, but that doesn’t mean that living beings are conscious or that they have interests and plans like we do. To think otherwise would be to accept some magical vitalist concept of life that science rejected long ago. Therefore, we can conclude that plants do not suffer, although they grow, reproduce and even fight their enemies with chemical responses. Likewise, we should accept that animals that lack a nervous system (like sponges) or that have only a rudimentary nervous system (like worms) do not suffer.

What about animals that do have a complex nervous system? Do they suffer? Here we must consider that suffering and pain are often confused, but in fact are not identical. Pain produces suffering, but suffering can be produced by things other than pain, generally speaking by negative emotional states. That pain and suffering are not identical is also shown by the fact that people may experience pain and not suffer from it. For example, the pain experienced when practicing some sports, when eating spicy food and by sexual masochists induces positive feelings instead of suffering. Some drugs called dissociative anesthetics (like ketamine) can selectively turn off the emotional part of pain leaving intact its sensory component: we are still able to feel the pain, but just don’t care about it. Given the complexity of this subject, I chose to divide this discussion into two parts: suffering that comes from physical pain and emotional suffering. I will start with the first.

Pain scientists distinguish between three concepts: nociception, pain and suffering. This distinction is even recognized by the Humane Society of the United States, an animal rights organization. To understand nociception consider the case of a patient who is undergoing surgery under general anesthesia. As the skin and organs of this person are being cut, pain sensory nerves faithfully record the damage and send this information to the spinal cord, which continues to the brain. The normal traffic of noxious signals only stop at the cerebral cortex because the large parts of the brain cortex is turned off by the general anesthetic [1, 2]. This basic processing of noxious information is what we call nociception. Of course, in an awake person nociception leads to pain. The important idea, however, is that the processing of information concerning physiological damage involving millions of neurons and sophisticated neural pathways does not imply the existence of pain. In fact, nowadays pain is considered part sensation part emotion; because fundamental aspects of pain are its negative valence (we dislike it) and its salience (we cannot avoid paying attention to it). Pain requires a fairly complex nervous system capable of turning sensations into emotions. Based on these ideas, I think it is reasonable to infer that animals that lack a nervous system of enough complexity do not feel pain, they just have nociception. Behavior consisting in avoiding a noxious stimulus should not necessarily be taken as an indication of pain. After all, even plants react to noxious stimuli. It is difficult to draw the line between animals that have just nociception and those that experience pain. However, it is clear that many animals do not come even close to having a nervous system complex enough to produce the sensation of pain with its associated negative emotions. Animals like the pond snail (11,000 neurons) or the sea slug (28,000 neurons) just don’t have this capacity. By comparison, we have 100 millions neurons just in our gut (the enteric nervous system) and 86 billion neurons in our brain. Of the invertebrates, the only animal that comes close is the octopus, with 300 million neurons, comparable with the rat’s 200 million neurons. This is why countries like the UK and Canada now give cephalopods (octopi, squids and cuttlefish) the same protections given to vertebrates. Of course, the number of neurons is not the only metric to measure the complexity of a nervous system, but using other metrics like number of synapses or overall capacity to process information will give similar results. A table of the number of neurons in different animal species can be found here.

But what most people are concerned about are the most complex animals, the mammals and the birds, which we eat, have as pets and use in scientific research. What about them? Do they feel pain? Do they suffer?

A lot can be learned about the relationship between pain and suffering in mammals by studying brain areas involved in the processing of pain in the brain. As I indicated above, pain has a sensory aspect and an emotional aspect. The sensory aspect of pain is processed by the somatosensory cortex, an area shaped like a hairband going from the top to the sides of the brain. It contains a detailed map of the body and processes pain and touch, telling us where these sensations originate (nowadays it is recognized that the dorsal posterior insula also contains a map of the body and is responsible for judgements on the localizations and intensity of pain). The somatosensory cortex is connected to the orbitofrontal cortex, located at the front end of the brain and whose function is to plan actions according with the information it receives. But neither the somatosensory nor the orbitofrontal cortex are responsible for the emotional component of pain. This function is assigned to two other areas of the cortex: the insula and the anterior cingulate cortex (ACC). Generally speaking, the function of the insula is to tell us how bad pain feels and to associate that emotion with a host of other emotions like sadness, fear, anger, joy, disgust and pleasure. Emotions can be understood as motivational states of the brain: they predispose us to act in a certain way, organizing everything we feel in a hierarchical way according to what we need to do. Pain is an emotion that motivates us to stop or escape from whatever is hurting us. This urgent motivational aspect of pain is processed by the ACC. So we could say that the insula and the ACC work together to turn pain into suffering by giving it its “I don’t like it” and “I want to stop it” qualities.

Recent discoveries have revealed that during the evolution of primates (monkeys, apes and humans) there was a reconfiguration of the brain pathways that process pain, culminating with the appearance of completely new pain processing areas in the human brain [2, 3]. To convey the importance of these changes, I must quickly summarize the neural pathways that carry pain signals from the body to the cerebral cortex. Noxious signals are carried by specialized fibers in the nerves from any part of the body to the dorsal horn of the spinal cord (see figure below). From there, the signals travel to the parabrachial nucleus in the brain stem, where they branch out to different nuclei of the thalamus and the forebrain [3]. Located in the middle of the brain, the thalamus function as the central relay of all sensory information, with its different parts or nuclei handling visual, auditory, gustatory, tactile and pain information. Different thalamic nuclei send pain signals to the four areas of the cortex described above: the somatosensory cortex, the orbitofrontal cortex, the insula and the ACC. These pain pathways are present in all mammals, but in primates a new additional pathway emerged that directly links the spinal cord with the nucleus of the thalamus connected to the insula, bypassing the parabrachial nucleus. This means that pain sensations are able to directly reach the part of the cortex where feelings are created. In humans, the size of this direct pathway between the thalamus and the insula is much larger anatomically, and much larger and more complex than in monkeys.

But is there another change in the brain that is unique to humans and a small number of other species including elephants and cetaeceans, but not being found in monkeys: a new part of the insula called the anterior insula [4, 5]. A.D. Craig, a scientist who has studied these changes by mapping the brains of monkeys, apes and humans, thinks that the posterior insula serves to create an emotional map of the state of the body in each moment. The anterior insula, on the other hand, serves to model the state of the body as it was in the past or in hypothetical situations in the future: “if this were to happen, that’s what I would feel”. Craig thinks that this gives us self-awareness by modeling feelings that represent the interior state of the body through time. The representation of hypothetical states of the body performed by the anterior insula is probably also responsible for empathy, the ability to feel what another person is feeling by simulating his body state in our own brain. In relation to suffering, we can see how growing relevance of the insula in generating the negative emotions associated with pain progressively increase the depth of suffering. This process culminates with humans; we are not only able to experience the pain of the present but are also aware of ourselves as beings that have suffered in the past and that may suffer in the future. Animals that lack an anterior insula would not be able to experience this type of suffering. The gradual appearance of the anterior insula in apes like bonobos and chimpanzees seems to correlate with the development of empathy and positive social emotions [4, 6].

In summary, we need to take a gradualist approach when considering the presence of pain and suffering in animals. Invertebrates, with the possible exception of cephalopods, do not appear to have a nervous system complex enough to feel pain, let alone suffering. Their behavior can be explained by simple responses to nociceptive signals. Vertebrates, particularly the ones with highly complex nervous systems like mammals and birds, do experience pain and quite probably suffer from it. However, the deep suffering that we experience as humans beings, rooted in our memory and our capacity to imagine the future, does not seem to exist other than in a rudimentary form in other mammals. Although animals have memories, without an anterior insula they cannot use them to construct a vivid representation of their past suffering, like we do. A measure of self-awareness and deep suffering exists in elephants and cetaceans, which also have a highly developed anterior insula and ACC with von Economo neurons.

Jeremy Bentham and Peter Singer failed to understand the true nature of suffering when they came up with the idea of speciesism. Just like we do not give the same moral status to animals and plants, we cannot give the same moral status to all animal species. When deciding how we should treat them we need to take into consideration whether they can feel pain and, if they do, how they suffer from that pain. The suffering of a mouse, a dog, a monkey and a chimpanzee are not equivalent. By the same token, human suffering has to be given a higher ethical consideration than the suffering of other animals. There is a moral imperative to diminish suffering in all sentient beings, but when difficult choices have to be made, human suffering has to come first. If saying this makes me a speciecist, I will wear that label with pride. But I’d rather call myself a humanist, because for me the priority is to decrease human suffering.

Juan Carlos Marvizon, Ph.D.

The author wishes to thank Dr. Bud Craig for his helpful comments

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