Comparative Psychology: Implications for Ethics, PA Dreves
nervous system, COMPARATIVE PSYCHOLOGY, experience, organisms, nervous systems, mammals, invertebrates, psychological distress, vertebrates, ability, neurons, cerebral cortex, suffering, emotion, organism, optic lobes, octopus brain, memory formation, intelligence, Digital image, complexity, C. elegans, invertebrates and vertebrates, limbic system, East Tennessee State University, Roth & Dicke, systems, nociceptors, complex functions, optic lobe, central nervous system, the nervous system, Octopus vulgaris, Fish Brain, octopi, self-awareness, conscious experience, visual ability, mouse brain, experience pain
Comparative Psychology: Implications for Ethics Parker A. Dreves East Tennessee State University
Comparative Psychology: Implications for Ethics Comparative psychology is primarily concerned with studying the nervous system
s and behaviors of non-human organisms. Traditionally, comparative psychologists have studied the nervous systems of these organisms in order to draw inferences about the structure, development, or functioning of the human nervous system. However, the study of comparative psychology can also be undertaken for other reasons such as informing our methods of domestication or the ethical treatment of animals
. The aim of this review will be to first examine a variety of nervous systems. Organisms will be discussed with respect to the structure, complexity, and function of their nervous system. The purpose of this will be to roughly delineate the varying levels of awareness found in animals. Following this examination of various nervous systems, this review will then move on to a discussion section. This section will address questions pertaining to pain and suffering in animals and, ultimately, how comparative neuroscience can inform our sense of ethics toward these organisms. Through the extensive history of this planet, the process of natural selection
has given rise to many diverse forms of life - many of which developed nervous systems. Nervous systems arose as an adaptive mechanism which endowed organisms with the ability to perceive, navigate, and manipulate their environments. The complexity of the nervous system varies widely from organism to organism. To make the study of nervous systems manageable, it is necessary to first divide organisms with nervous systems into two categories: invertebrates and vertebrates. Invertebrates are organisms which lack a backbone. Some common types of invertebrates include annelids, mollusks, crustaceans, arachnids, and insects. Invertebrates are by far the most abundant forms of life, accounting for 97% of life on earth (Buchsbaum, Buchsbaum, Pearse, & Pearse, 2013). Given this, it is apparent that even within the category of invertebrates there is still a great degree of variation in the structure and complexity of nervous systems. As such, this paper will examine the nervous systems of a few selected organisms that can be seen as roughly representing the varying degrees of complexity within invertebrates.
It is logical to first begin by examining one of the simplest nervous systems. Among invertebrates, nematodes are commonly recognized as being the most primitive. Nematodes are roundworms and are found in almost every environment on Earth. Among nematodes, C. elegans is by far the most thoroughly researched. C. elegans has an extremely simple nervous system, made up of 302 neurons (White, Southgate, Thompson, & Brenner, 1986). Despite the relatively low number of neurons, C. elegans has a nervous system which forms about 7,500 synapses (White et al., 1986). In addition to having 302 neurons, this organism possesses 56 glial cells (Oikonomou & Shaham, 2011). The organization of the neurons in this organism is quite simplistic. First, it is important to note that the majority of the neurons in C. elegans are located in the head, grouped into ganglia. In addition to the neuron clusters in the head, C. elegans has a neuron tract that runs along the entire belly of the organism, creating the ventral cord. At the end of the ventral cord, near the tail, there is another smaller ganglia.
This is an image of the entire nervous system of the nematode C. elegans. All 302 neurons! Image Citation: Hutter, H. Neurons of C. elegans. digital image
. Simon Frasier University. N.p., n.d. Web. . Of the 302 neurons that C. elegans possesses, about one fourth of these are sensory neurons. These sensory neurons are distributed based on function. For example, chemosensory neurons are clustered near the front of the ganglia in the head, and extend their dendrites to chemoreceptors in the nose. Other specialized neurons responsible for detecting tactile sensation and temperature are distributed along the
ventral cord. The remaining neurons in C. elegans are bundled into the head ganglion or are attached to muscles and organs, allowing for vital life functions and movement (White et al., 1986). It follows from the relative simplicity of the nervous system of C. elegans that the function and behavior of this organism is also relatively simple. C. elegans behaves in a very systematic way. Typically, C. elegans will move forward until it finds food. It displays an avoidance response (negative taxis) to some chemicals and it displays attraction (positive taxis) to chemicals signaling potential food sources (Dusenbery, 1974). If touched, C. elegans will move away from the source of the stimuli (Chalfie & Sulston, 1981). Furthermore, some researchers have suggested that C. elegans has nociceptors, and is thus capable of detecting damage to its body (Tobin & Bargmann, 2004). However, C. elegans certainly does not have the cognitive capacity to emotionally process this pain, as it possesses (unsurprisingly) no neuroanatomical basis for the experience of emotion. More interesting, however, is that even C. elegans has been shown to be capable of simple learning. Indeed, researchers have demonstrated both habituation and sensitization in C. elegans (Ardiel & Rankin, 2010). In this way, it seems that the nervous systems of even the simplest organisms can be programmed by the environment to some degree. However, although capable of habituation and sensitization, C. elegans is certainly not able to experience emotions, make predictions, form cognitive maps, or form any of the more complex associations seen in other organisms. By most accounts, this organism is not conscious. Insects In general, insects contain between about 100,000 and 1,000,000 neurons, forming as many as 10^9 synapses (Menzel & Giurfa, 2001). Insect nervous systems fit a fairly stable pattern. Most insects have a large cluster of neurons in the head, known as the head ganglion. This head ganglion can be divided into three parts: the protocerebrum, the deutocerebrum, and the tritocerebrum (Chapman, 1998). Insects are interesting, however, in that their nervous system is not as centralized as it is in vertebrates. Insects have
ganglia spread throughout the thorax and abdomen which control specific body segments. For example, where a human's leg is still controlled by the central brain, an insect's leg would be controlled by its own local ganglion. However, insects have a nerve cluster in the center in their body which allows these separate groups of ganglia to communicate. These ganglia spread throughout the body are connected to the head ganglion by a nerve that runs the length of the insect.
One of the three main sections of the head ganglion is the protocerebrum. This portion of the head ganglion is directly connected to photoreceptors in the insect's eyes and receives visual inputs. The deutocerebrum is connected to the antennae, which contains both mechanoreceptors and chemoreceptors. Finally, the tritocerebrum is responsible for controlling the insect's mouth parts during feeding. Importantly, the tritocerebrum also connects the head ganglion to the other ganglia spread throughout the body, allowing the insect to coordinate movement between body segments (Chapman, 1998). The size and function of the various ganglia can vary from insect to insect. For example, the fruit fly has a larger protocerebrum than most insects to accommodate large amount of information received from its compound eyes.
Note how the ganglia of insects are dispersed throughout the entire organism. Although it has a brain, this is only responsible for processing visual information, chemical information, and controlling the mouth. Contrast this with the nervous system of humans, which is highly centralized. The fact that the legs and digestive tract of insects are controlled by their own sets of ganglia explains why insects can still move around for days after being beheaded! Image Citation: Snodgrass, RE 1935. Principles of Insect Morphology. MacGraw-Hill Book Co., New York, figs 247.
Together, the head ganglion and the thoracic ganglia constitute the central nervous system of insects. However, there is also a collection of neurons which control functions such as digestion and hormone regulation. In insects, this is known as the stomodaeal nervous system (Burgess & Rempel, 1966). The stomodaeal nervous system extends from the tritocerebrum and contains a frontal ganglion, a hypocerebral ganglion, and gastric nerves. It is important to understand how the structure of the nervous system relates to behavior. Insects are adept at navigating their environment, finding food, and avoiding predators. Although movement is not localized as in the brains of humans, information can be relayed from the tritocerebrum to the segmental ganglia. Insects have indeed displayed a limited ability to learn. For example, fruit flies have been conditioned to avoid scents that they have associated with noxious chemicals (Mery & Kawecki, 2002). Furthermore, it has been proposed that some insects have a limited ability to form cognitive maps. Honey bees, for example, are able to find their way back to food sources. This has led some researchers to hypothesize that honey bees can determine their location relative to landmarks and even plan routes for reaching destinations (Gould, 1986). However, although capable of simple associations and spatial learning, it is unlikely that insects can make predictions, feel emotions, selfreflect, or contemplate to any degree. In addition, most insects do not have nociceptors, meaning that they have no capacity to feel pain (Eisemann et al., 1984). Cephalopods Among invertebrates, cephalopods are often noted as having the most complex nervous systems (and thus the most intelligent). To illustrate the complexity of the cephalopod nervous system, this paper will examine octopi (although cephalopods also includes squids and cuttlefish). The common octopus, Octopus vulgaris, has about 500,000,000 neurons (Young, 1963). Although about two thirds of these neurons are dispersed throughout the eight arms of the octopus, the rest of the neurons are clustered in the head. Notably, the octopus has developed a mass of about 50,000,000 organized neurons which constitute
a brain. Although the structure of the octopus brain likely looks foreign to us, it is indeed capable of many complex functions. The nervous system of Octopus vulgaris is divided into three main parts. Two of these parts, the optic lobes and the nervous system governing the tentacles, are located outside of the brain cavity. The optic lobes contain about 150,000,000 neurons (Young, 1962), which provides Octopus vulgaris the ability to process visual information exceptionally well. The nervous system of the tentacles contains about 300,000,000 neurons. This provides the octopus with a greatly developed sense of touch. In addition to receiving tactile sensory information, the tentacles also contain chemoreceptors, allowing the octopus to smell. Although the majority of the octopus's neurons lie in the periphery, this organism also has a substantially developed central brain, containing about 50,000,000 neurons. Among other functions, this central brain is responsible for the octopus's ability to form memories, remain balanced, and employ Executive functioning. The largest lobe of the brain of Octopus vulgaris is the vertical lobe. This lobe has been demonstrated to be used in memory formation (Boycott & Young, 1955). Because of the size of this lobe, octopi have relatively complex memories and learn quickly. Interestingly, some lobes of the octopus' brain contain gyri which is typically only seen in vertebrates. This is an adaptation which increases the surface area of the brain of Octopus vulgaris. Octopus brains are especially interesting because, although they are extremely intelligent, their brains evolved much differently than in vertebrates.
On the left is a mouse brain. On the right is an octopus brain. Notice how they are structured in completely different ways, although both display some level of intelligence. This goes to show that there is more than one way to develop intelligence. Image Citation: Shigeno, Suichi. Mouse Brain Compared to Octopus Brain. Digital image.ScienceMag. N.p., n.d. Web. .
Notice the relative size of the optic lobes in the octopus. This explains the acute visual ability that octopi display. The vertical lobe (in the middle) is responsible for memory formation. Image Citation: Octopus Nervous System. Digital image. Colorado.edu. N.p., n.d. Web. . As a result of its complex nervous system, Octopus vulgaris is capable of rather sophisticated behavior. Perhaps the most remarkable aspect is that Octopus vulgaris can learn through observation alone. This was exemplified in an experiment by Fiorito and Scotto (1992) in which an octopus was able to learn how to open a jar by merely observing another octopus complete the task. Octopi have also been known to make use of tools, which is certainly a complex behavior. An article by Finn, Norman, and Tregenza (2009) noted that octopi will gather coconut shells discarded by humans and use these to furnish "armor" for themselves. Octopi have also been observed arranging their living environments. This takes the form of carefully placing rocks or other bits of debris in specific locations around their dens. Octopi are notorious for being able to escape their tanks, due to their ability to learn how to use latches and handles. This has led some researchers to believe that octopi have some concept of what they want and that they can employ the necessary foresight and planning to make it so. Octopi are certainly the most intelligent invertebrates and likely possess cognitive ability at least on par with your household cat or dog, if not more so.
The discussion of nematodes, insects, and cephalopods by no means exhausts the discussion of invertebrate nervous systems, though it does display the widely varying levels of complexity and awareness among these organisms. The following section of this essay will proceed on to a discussion of vertebrate nervous systems. Vertebrates have much less variation in the structure of their nervous systems than do invertebrates. All vertebrate nervous systems fit a fairly consistent structure. As is noted by the name, all vertebrates have a spinal cord. Extending from the spinal cord are neurons which relay information from the peripheral sensory systems to the central nervous system. The central nervous system is comprised of the spine and the brain. All vertebrates have their brain located at the top of the spinal cord. Within the brain, all vertebrates have three brain regions. These include the hindbrain, midbrain, and forebrain, but the size and function of these regions varies among vertebrates. Since the basic structure of the nervous system is similar in all vertebrates, the main differences discussed will not be regarding the layout of the nervous system, but rather regarding the specific brain structures that each class of organisms possesses. Fish Fish are arguably the most primitive of the vertebrates. As such, the largest portion of the fish brain is the hindbrain. This portion of the brain contains the pons and medulla oblongata. These structures govern non-conscious processes such as heart rate and respiration. Fish also have a fairly well developed cerebellum, which allows them to maintain orientation while swimming. Fish have a small midbrain which contains their optic lobe. The forebrain in fish is primarily devoted to olfactory perception, though fish do have a very small cerebrum. The cerebrum of fish contains the pallium. Through experimentation, it has been determined that the pallium is used both in emotional responses and in memory formation (Nieuwenhuys & Meek, 1990). This is especially interesting, as it suggests that fish may indeed experience some type of emotion.
Due to their relatively simple brains, it is often thought that fish operate via reflexive behaviors. Even so, fish are capable of associative learning. For example, it has been observed that goldfish could remember the color of a tube that dispensed food for up to a year (Brown, Laland, & Krause, 2006). Other types of fish can learn to avoid locations where they have been previously attacked. The fact that fish can avoid certain locations of course suggests that fish can form some type of cognitive map and can identify locations. This ability to form memories like this is certainly a function of the pallium. In a study conducted by Portavella, Torres, and Salas (2004), it was found that lesions to the medial telencephalic pallia removed avoidance behavior that the fish had previously learned. In this way, it was deduced that the pallium is crucial for the retention of memories in fish. Indeed, although their brain structures seem relatively undeveloped, fish are still capable of many forms of learning. This should come as no surprise though, considering that even C. elegans was capable of extremely simplistic conditioning. Finally, fish have been demonstrated to have nociceptors and are thus capable of experiencing some form of pain (Sneddon, Braithwaite, & Gentle, 2003). This depicts the organization of brain structures in fish. The pallium is part of the telencephalon, which is located in this image by what is labeled as "cerebral hemisphere". Image Citation: Truong, Melissa, Scott Lawrence, and David Graham. Fish Brain. Digital image. MarineBio.mbhs.edu. N.p., n.d. Web. .
The nervous systems of birds, although varied, are generally more complex than those of fish. Birds, like fish and all other vertebrates, have a hindbrain that is responsible for vital functions. However, the cerebellum in birds is much larger. This is a result of having to coordinate the complex muscle activity used in flight. Birds also have a much larger midbrain to accommodate the more complex sensory information from their well-developed eyes. Finally, birds differ from fish in the size of their forebrain. This is a result of having a much larger cerebrum. Often, the size of the cerebrum is equated with intelligence. Indeed, birds display much more complex behavior as compared to fish. Some of Skinners most notable experiments were performed on pigeons, which could be easily conditioned. This research was applied through training homing pigeons which were trained to deliver messages. This indicates that birds are capable of being not only conditioned but also forming very detailed cognitive maps. In addition to this, many birds have the ability to use language by using songs to convey meaning to other birds. Once a song in learned, a bird will retain the song for its entire life. Although some may think that this ability is merely the result of conditioning, this is not the case. Birds, like humans, have a critical period for learning their vocalizations. In fact, there are many parallels between human language and bird songs. Both humans and birds have specialized forebrain regions used in language production and comprehension (Doupe & Kuhl, 1999). Birds are dynamic organisms with a great capacity to learn and communicate. This is surely a result of their highly developed hypothalamus and cerebrum. Birds have also been demonstrated as having emotions. Evidence for this comes primarily from behavioral tests, though there is reason to suspect that they have emotion based purely off of neuroanatomy. A test by Cabanac and Aizawa (2000) examined physiological measures of stress in roosters. Results of this test revealed that roosters had increased hypertension and body temperature when placed in stressful situations. Further support for emotion in birds comes from the presence of a limbic
system. In birds, the pallial-limbic system is comprised of the association pallium, the striatum, and the hypothalamus (Izawa, Nishizawa, & Watanabe). Although this organization is slightly different from that of mammals, it nevertheless allows for birds to feel emotion.
Contrasted with the diagram of the fish brain above, it becomes apparent that birds have a much more developed brain. Specifically, the cerebrum is much larger, allowing for more complex learning. Image Citation: A Bird's Brain. Digital image. Birdsaretheword s. N.p., n.d. Web. .
Among vertebrates, mammals are often regarded as having the most developed brains. Although the hindbrain is relatively the same in mammals as in fish and birds, the midbrain and forebrain have many new structures. First, all mammals have a limbic system containing the hippocampus an amygdala. These structures give mammals the ability to experience emotions and aids in forming detailed memories. Perhaps the most notable addition in mammals is the increased surface area of the cerebrum, giving rise to the cerebral cortex. Although this varies in size among mammals, this addition allows for complex computations of information. The cerebral cortex allows the use of logic, planning, language, introspection, and the generation of novel ideas (Roth & Dicke, 2005). Although humans -possessing 23 billion neurons in the cerebral cortex alone- certainly lead the pack in this respect, all mammals possess a cerebral cortex to some degree.
The size of the cerebral cortex of mammals is often associated with intelligence (Roth & Dicke, 2005). As there is a great deal of variation in the size of the cerebral cortex within mammals, the following table summarizes the number of neurons in the cerebral cortex for some well-known animals. Note that this is not the number of neurons in the whole organism, or even in the whole brain, but specifically in the cerebral cortex. Mouse: 4,000,000 (Roth & Dicke, 2005) Rat: 21,000,000 (Korbo et al., 1990) Dog: 160,000,000 (Roth & Dicke, 2005) Cat: 300,000,000 (Roth & Dicke, 2005) Horse: 1,200,000,000 (Hofman & Falk, 2012) Dolphin: 5,800,000,000 (Hofman & Falk, 2012) Chimpanzee: 6,200,000,000 (Roth & Dicke, 2005) Elephant: 11,000,000,000 (Hofman & Falk, 2012) Human: 23,000,000,000 (Herculano-Houzel, 2009)
The total number of neurons in the entire organism is of course much greater than the number of neurons in just the cerebral cortex. Humans, for example, have 23,000,000,000 neurons in the cerebral cortex alone, but 86,000,000,000 neurons in the entire organism (10^14 10^15 synapses). Image Citation: Cerebral Cortex of Animals. Digital image. CNX Biology, n.d. Web. . The size of the cerebral cortex is certainly reflected in the complexity of the organism's behavior. Mice, falling at the low end, seem to possess very little ability to plan and make complex judgments. Although capable of memorizing mazes and even using observational learning, mice cannot use tools, plan ahead, or use language. As the number of neurons in the cerebral cortex increases, behavior becomes more complex. For example, the last four animals on the list (Dolphins, Chimpanzees, Elephants, and Humans) have all been observed using tools. Tool use is often considered to be a mark of higher intelligence, as it requires analyzing the environment and putting certain aspects of it to use for a certain end. Other tests of intelligence include tests of problems solving (such as accessing an out-of-reach food source using tools), memory, attention, image discrimination, communication, and more. Each group of mammals will perform differently on such tests, suggesting a correlation between size of the cerebral cortex and intelligence.
Another interesting test is a test for self-awareness, known as the mirror test (Gallup, Anderson, & Shillito, 2002). In such test, an animal is presented with a mirror. If the animal is able to recognize the image in the mirror as itself, it is considered to possess self-awareness. As with tool use, the animals who are capable of this are ones that have relatively large cerebral cortices. Most primates are able to pass the mirror test, as well as dolphins, whales, and elephants. Based on both behavior and neuroanatomy, it can be concluded that mammals are capable of feeling pain as well as the emotional processing associated with it. Although this may vary in degree, there are enough similarities to conclude that all mammals can suffer to some extent. Mammals all have developed limbic systems which aid in memory and learning. It can be said that mammals all experience consciousness to some degree. Discussion: The essay thus far has examined the variety of nervous systems in both invertebrates and vertebrates. In general, invertebrate nervous systems are less centralized than vertebrate nervous systems. Most invertebrates have body segments that are controlled by clusters of ganglia, rather than an executive brain. Vertebrates, on the other hand, all have centralized nervous systems composed of the brain and spinal column. Within vertebrates, the cerebral cortex is most often associated with intelligence. However, it should also be noted that the cerebral cortex is not necessary for intelligence. This can be seen in the case of octopi who, despite having a radically different brain structure than vertebrates, are still regarded as extremely intelligent creatures. Ultimately, the study of nervous systems should allow us to understand what these organisms experience and what they are capable of. The final portion of this essay will discuss the implications of this information. The varying degrees and types of consciousness have been debated by many philosophers and scientists. Questions they have posed have included: Do non-human animals experience consciousness? Do non-human animals have the
capacity to feel pain? How is this related to suffering? Finally, how should we shape our system of ethics to include (or exclude) certain forms of life? It is my belief that all of these questions can be answered through the detailed study of nervous systems. Although we may lack some of the information necessary to answer these at this time, it is nevertheless possible. Keeping in mind the previous discussion of nervous systems, the remainder of this essay will examine these questions.
1) Do non-human animals experience consciousness? The short answer is both yes and no. The answer is "no" in the sense that non-human animals likely do not experience a consciousness that is anything like our own. However, the answer is "yes" in that non-human animals certainly possess some awareness of the world around them and have the ability to navigate it effectively. Due to the wide variety in nervous system structures, it is likely that consciousness comes in degrees. It is not just a matter of having consciousness or not having consciousness, but is also a matter of the degree to which the organism possesses consciousness. We could likely all agree that C. elegans, with its 302 neurons, does not have a conscious experience (or at least not a remarkable one). The functioning of this organism can be thought of as relatively "robotic" without any real thinking taking place. The behavior of this nematode is no more conscious than a reflex arc in a human. However, as we increase in the complexity of the nervous system, the question of consciousness becomes more difficult to answer. As we have seen, even insects have quite intricate and complex nervous systems. Again, however, I am hesitant to claim that consciousness is present. Although insects can learn and navigate, it could be argued that none of this is consciously accessible to the insect. In this way, all learning in insects would be implicit. Without a centralized brain, it is difficult to see how memories could be directly accessible to the insect. However, this does not rule out that insects are conscious to a lesser degree than humans. Indeed, some scientists have argued that insects do possess a rudimentary form of consciousness.
Insects, particularly the Honey Bee, have been subjected to rigorous behavioral tests. Evidence from these tests suggests that Honey Bees can form short and long-term memories, form cognitive maps, and even relay these maps to other bees through a series of dance-like behaviors. Although it is unknown if insects such as these experience consciousness, they nevertheless have many cognitive tools at their disposal which allow them to navigate the environment and learn. Some insect biologists have conceded that although insects do not ponder or "think" per say, they are certainly present in the moment and experience the environment around them. Whether or not this ability constitutes consciousness is still up for debate. The more complex invertebrates, such as octopi, are often regarded as being conscious. This is based on both behavior and neuroanatomy. These organisms display a remarkable ability to navigate, manipulate, and make decisions regarding their environment. Octopi can also form both short and longterm memories, and generate novel ideas. This is a very important aspect of octopus intelligence. The ability to be presented with a new situation and come up with a novel response reflects some degree of original thinking or pondering. It reflects not only the ability to form mental representations, but also the ability to manipulate these mental representations. This aspect of consciousness is likely what sets humans and octopi apart from insects. Mammalian consciousness most likely resembles what we, as humans, would recognize as consciousness. This is of course no surprise, as we are mammals ourselves. Based on the neuroanatomy and behavior of other mammals, it can be concluded that they experience many of the same things we do. That is to say that they experience the immediate environments, form memories, feel emotions, and can respond to stimuli in learned or innate ways. Although other mammals lack the logical processing that humans possess, it can be argued that they have some conscious experience. Indeed, consciousness should not just be seen as either present or not present, but should also be examined in terms of the degree that it is present. Consciousness comes in many varying degrees and types. Different aspects of consciousness could include the ability to experience the immediate environment, form mental representations of objects and places, respond to stimuli in some way that is
either learned or innate, have a sense of self, experience emotion, and the ability to create novel ideas. Ultimately, the structure and complexity of the nervous system will determine if an organism is capable of all or just a few of these abilities, which can tell us about their conscious experience.
2a) Do non-human animals feel pain? Pain is commonly defined as the ability to detect damage to one's body and to react aversively to this stimulus. Of key importance to the debate of pain is the presence of nociceptors. Nociceptors are a type of sensory neuron which respond specifically to potentially damaging stimuli. Organisms which lack nociceptors are typically not considered as being able to experience pain. Organisms with nociceptors are typically regarded as having the capacity to feel pain. All vertebrates possess nociceptors. This includes fish, birds, reptiles, amphibians, and mammals. As a result, all of these organisms are capable of detecting pain. In addition, most invertebrates possess nociceptors, with the large exception of insects. Most insects do not have nociceptors and thus do not feel pain. However, there are a few exceptions even here. For example, the fruit fly has been found to possess nociceptors. Other invertebrates such as octopi, crustaceans, and nematodes do possess nociceptors.
2b) Do non-human animals suffer? It is important to note here that the ability to feel pain and the ability to suffer are separate, although related. The ability to feel pain does not guarantee the ability to suffer. Suffering differs from merely detecting pain in that suffering entails some amount of psychological distress, typically characterized by an emotional response. Take the classic example of placing your hand on a hot stove. Although you certainly display a pain reaction -quickly moving your hand away from a potentially damaging stimulus- there is no resulting psychological distress. Although nociceptors detected tissue damage and triggered a reflex response, it did not necessarily entail suffering at the emotional level. On the other hand, consider finding one day that your entire body is paralyzed. Although you can feel no pain whatsoever, you likely would
experience immense psychological distress, and are thus suffering. These examples depict the ways in which pain and suffering are distinct from one another. Although it is often the case that physical pain entails psychological suffering. The rest of this section will examine what psychological capacities are necessary for suffering to be experienced. There are a few differing theories on what is necessary for suffering. Some would claim that a sense of self is necessary for suffering to be experienced. As proponents of this idea would hold, an organism cannot suffer unless it is aware enough of itself to comprehend what is happening to it. However, this view that self-awareness is necessary for suffering would endow only a very select few organisms with this ability. At it currently stands, we only have evidence that primates, dolphins, elephants, and (interestingly) magpies possess self-awareness. The test currently used to test for selfawareness is the mirror test, in which an animal is tested to see if it will recognize itself in a mirror. This test has been criticized for a few reasons, however. As such, it is difficult to say whether or not we can actually determine self-awareness in other animals. Assuming, however, that our current tests of selfawareness are accurate and that suffering is only possible in self-aware beings, only a small handful of animals would actually be able to suffer. On the other hand, many have argued that possessing self-awareness is setting the bar too high in terms of the ability to suffer. Others argue that all that is needed to suffer is the ability to experience emotion. Proponents of this point to cases of abused animals (which have not passed the self-awareness test) who display, as they would tell it, very apparent signs of psychological distress and disturbed emotions. For example, neglected or abused animals will display symptoms of depression (i.e. not eating, withdrawing from any activity). Other proponents of this note the altered behavior and decreased life span of animals in captivity as evidence of psychological distress. Although these are all behavioral inferences, there is a neurological basis for taking these observations seriously. As noted earlier, all mammals possess the brain structures responsible for producing emotion. Indeed, it is likely no coincidence that mammals, more so than any other group of organisms, display the behaviors associated with psychological suffering. In addition to mammals being capable of suffering
some evidence has pointed toward birds having emotion as well (although governed by different brain structures). In any case, the presence of emotions seems to be closely linked with the ability to suffer psychologically. If this is the indeed the case, then any animal which possesses the structures necessary for producing emotion (the limbic system or an analogous system) can also suffer. This would almost certainly include mammals and birds. Suffering in fish and amphibians is still being debated. Insects (and most other invertebrates) are generally not considered as having the capacity to suffer psychological distress.
3) How should our understanding of nervous systems inform our sense of ethics regarding the treatment of non-human organisms? As noted by the previous discussion, examining an organism's nervous system and behavior can inform us as to the extent to which it can experience suffering. Strictly speaking, our consideration of ethics should extend to those organisms which we have good reason to believe are capable of suffering. This ethical framework is a form of consequentialism, which states that some states of being, actions, or things better or worse than others. Consequentialist theories, unlike other ethical frameworks, can be easily extended to non-human organisms. The idea would be to identify suffering as a state of being that is to be avoided. The aim would be to then identify organisms which are capable of experiencing suffering and to treat them in such a way as to minimize this experience. With this in mind, it seems that we can exclude most invertebrates from ethical consideration. This is because the vast majority of invertebrates do not have the nervous system structures necessary for either nociception, the emotional processing of pain, or both. Insects, for example, have been thoroughly demonstrated to lack any pain responses such as limping or nursing. Since crustaceans have nervous systems organized in very similar ways as insects, and even very similar numbers of neurons, the same can likely be concluded for them. Furthermore, invertebrates do not have the neural capacities for experiencing emotion. If emotion is indeed necessary for suffering, then organisms that lack emotional capacities would therefore not be able to suffer.
As far as invertebrate ethics is concerned, the one exception to this may be highly intelligent cephalopods, such as octopi. Even so, the evidence is still mixed as to whether octopi can suffer. Although octopi will react to noxious stimuli and can learn to avoid such stimuli, it is still unknown whether or not they have the cognitive experience of suffering. As it currently stands, there is not an agreement on whether or not cephalopods can suffer. For the time being, however, it seems better to air on the side of extending our ethical concerns to cephalopods as well. Indeed, legislation protecting cephalopods has been passed in many countries. For example, the European Union now extends the same regulations to cephalopod research as it does to research on mammals. Other that the European Union, however, Canada is the only other country which regulates the treatment of cephalopods. The United States Animal Welfare Act does not currently include cephalopods. Ethical consideration becomes more important in vertebrates. All vertebrates have the ability to feel pain and experience some emotion, although it may vary in type and degree. As noted earlier, even fish have a brain structure called the pallium which has been hypothesized to play a role in emotional responses. If fish can indeed experience emotions, then they may well be capable of suffering. Although this notion may go against commonly held conceptions of what fish can and cannot experience, it may indeed be the case. Fish likely experience pain and emotions in a very different way than humans do, but there is reason to believe that fish can experience some form of suffering. If this is supported by future research, then fish too should be included in ethical considerations. Finally, there is a general consensus that both birds and mammals warrant ethical consideration. There is behavioral evidence as well as anatomical basis for believing that both of these classes of vertebrates can indeed suffer psychological distress. As such, we should adjust our behavior towards these organisms in order to reduce the amount of suffering. Of course, there are many instances in which animal suffering is necessary to reach certain human ends. The two domains in which ethicists generally have complaints are in our treatment of livestock and in our treatment of laboratory animals. Although it is not likely that either of these practices will be ended, we should be careful to pursue these endeavors as humanely as possible. In the realm of livestock,
we can ensure that animals are allowed to live in a way that is not psychologically damaging before their death. This notion is what has been behind the movement for "free-range" livestock. Although these animals will still be used for food, they are not subjected to unnecessary cruelty and confinement during their lives. Indeed, many European countries as well as Canada have implemented regulations on the conditions animals can be raised in. These laws prevent the mutilation of animals, prevent the isolation of animals, and ensure that developmental, physiological and ethological needs of animals are met. Although the United States Animal Welfare Act protects animals used in biomedical research, testing, teaching and exhibition, it grants no protection to animals raised for food. This is a spurious distinction and it is my feeling that the Animal Welfare Act should be extended to all animals, regardless of their intended purpose. Although some groups have raised concerns about the ethical treatment of animals in laboratories, I would like to point out that these concerns are negligible. This is for three reasons. First, animals used in research are already protected by the Animal Welfare Act. Second, the number of animals used in research is negligible in comparison to the number of animals slaughtered each year for consumption. Finally, animal research is often done in the name of a much nobler purpose than becoming a Big Mac. Animal research allows advances in medicine, psychology, genetics, and many other fields. Much of the research conducted on animals will be used to better the lives of both humans and animals. Because of this, we should recognize that some amount of animal suffering for research is acceptable. It can be viewed as a sort of "ethical tradeoff", sacrificing the well-being of a few animals for the long term promotion of well-being in both humans and animals.
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