To say that a being deserves moral consideration is to say that there is a moral claim that this being has on those who can recognize such claims. A morally considerable being is a being who can be wronged in the morally relevant sense. It is generally thought that all and only human beings make such claims, however, when we ask why it is thought that all and only humans are the types of beings that can be wronged, answers are not particularly easy to come by. Humans are members of the species Homo sapiens. But species membership does not explain why there is a moral claim made by those that belong to this species and not other species. That humans are members of the species Homo sapiens is certainly a distinguishing feature of humans -- humans share a genetic make-up and a distinctive physiology, but this is unimportant from the moral point of view. Species membership is a morally irrelevant characteristic, a bit of luck which is no more morally interesting than being born male or female, Malaysian or French. Thus species membership itself cannot support the view that members of one species, namely ours, deserve moral consideration that is not owed to members of other species. Of course, one might respond that it is not membership in a biological category that matters morally, it is our humanity that grounds the moral claims we make. Humans are morally considerable because of the distinctively human capacities we possess, capacities that only we humans have.
But which capacities mark out all and only humans as the kinds of beings that can be wronged? A number of candidate capacities have been proposed—developing family ties, solving social problems, expressing emotions, starting wars, having sex for pleasure, using language, or thinking abstractly, are just a few. As it turns out, none of these activities is uncontroversially unique to human. Both scholarly and popular work on animal behavior suggests that many of the activities that are thought to be distinct to humans occurs in non-humans. For example, many species of non-humans develop long lasting kinship ties—orangutan mothers stay with their young for eight to ten years and while they eventually part company, they continue to maintain their relationships. Less solitary animals, such as chimpanzees, baboons, wolves, and elephants maintain extended family units built upon complex individual relationships, for long periods of time. Meerkats in the Kalahari desert are known to sacrifice their own safety by staying with sick or injured family members so that the fatally ill will not die alone. All animals living in socially complex groups must solve various problems that inevitably arise in such groups. Canids and primates are particularly adept at it, yet even chickens and horses are known to recognize large numbers of individuals in their social hierarchies and to maneuver within them. One of the ways that non-human animals negotiate their social environments is by being particularly attentive to the emotional states of others around them. When a conspecific is angry, it is a good idea to get out of his way. Animals that develop life-long bonds are known to suffer terribly from the death of their partners. Some are even said to die of sorrow. Darwin reported this in The Descent of Man: "So intense is the grief of female monkeys for the loss of their young, that it invariably caused the death of certain kinds." Jane Goodall's report of the death of the healthy 8 year old chimpanzee Flint just three weeks after the death of his mother Flo also suggests that sorrow can have a devastating effect on non-human animals. (see Goodall 2000, p. 140-141 in Bekoff 2000). Coyotes, elephants and killer whales are also among the species for which profound effects of grief have been reported (Bekoff 2000) and many dog owners can provide similar accounts. While the lives of many, perhaps most, non-humans in the wild are consumed with struggle for survival, aggression and battle, there are some non-humans whose lives are characterized by expressions of joy, playfulness, and a great deal of sex. Recent studies in cognitive ethology have suggested that some non-humans engage in manipulative and deceptive activity, can construct "cognitive maps" for navigation, and some non-humans appear to understand symbolic representation and are able to use language. It appears then that most of the capacities that are thought to distinguish humans as morally considerable beings, have been observed, often in less elaborate form, in the non-human world. Because human behavior and cognition share deep roots with the behavior and cognition of other animals, approaches that try to find sharp behavioral or cognitive boundaries between humans and other animals remain controversial. For this reason, attempts to establish human uniqueness by identifying certain capacities, like those discussed in this paragraph and perhaps others, are not the most promising when it comes to thinking hard about the moral status of animals.
Nonetheless, there is something important that is thought to distinguish humans from non-humans that is not reducible to the observation of behavior best explained by possessing a certain capacity, namely our "personhood." The notion of personhood identifies a category of morally considerable beings that is thought to be coextensive with humanity. Historically, Kant is the most noted defender of personhood as the quality that makes a being valuable and thus morally considerable. In the Groundwork, Kant writes:
...every rational being, exists as an end in himself and not merely as a means to be arbitrarily used by this or that will...Beings whose existence depends not on our will but on nature have, nevertheless, if they are not rational beings, only a relative value as means and are therefore called things. On the other hand, rational beings are called persons inasmuch as their nature already marks them out as ends in themselves. (Kant, 1785, 428)
And in the Lectures on Anthropology:
The fact that the human being can have the representation "I" raises him infinitely above all the other beings on earth. By this he is a person....that is, a being altogether different in rank and dignity from things, such as irrational animals, with which one may deal and dispose at one's discretion. (Kant, LA, 7, 127)
More recent work in a Kantian vein develops this idea. Christine Korsgaard, for example, argues that humans "uniquely" face a problem, the problem of normativity. This problem emerges because of the reflective structure of human consciousness. We can, and often do, think about our desires and ask ourselves "Are these desires reasons for action? Do these impulses represent the kind of things I want to act according to?" Our reflective capacities allow us and require us to step back from our mere impulses in order to determine when and whether to act on them. In stepping back we gain a certain distance from which we can answer these questions and solve the problem of normativity. We decide whether to treat our desires as reasons for action based on our conceptions of ourselves, on our "practical identities." When we determine whether we should take a particular desire as a reason to act we are engaging in a further level of reflection, a level that requires an endorseable description of ourselves. This endorseable description of ourselves, this practical identity, is a necessary moral identity because without it we cannot view our lives as worth living or our actions as worth doing. Korsgaard suggests that humans face the problem of normativity in a way that non-humans apparently do not:
A lower animal's attention is fixed on the world. Its perceptions are its beliefs and its desires are its will. It is engaged in conscious activities, but it is not conscious of them. That is, they are not the objects of its attention. But we human animals turn our attention on to our perceptions and desires themselves, on to our own mental activities, and we are conscious ofthem. That is why we can think about them…
And this sets us a problem that no other animal has. It is the problem of the normative.... The reflective mind cannot settle for perception and desire, not just as such. It needs a reason. (Korsgaard, 1996, 93)
Here, Korsgaard understands "reason" as "a kind of reflective success" and given that non-humans are unable to reflect in a way that could be "successful," it would appear that they do not act on reasons, at least reasons of this kind. This failure to have reasons to act provides a basis upon which moral consideration can be denied. Since non-humans do not act on reasons they do not have a practical identity from which they reflect and for which they act. So humans can be distinguished from non-humans because humans, we might say, are sources of normativity and non-humans are not.
Yet Kant's view of personhood and Korsgaard's sophisticated personhood account cannot distinguish all and only humans as morally considerable. Personhood is not, in fact, coextensive with humanity when understood as a general description of the group to which human beings belong. And the serious part of this problem is not that there may be some extra-terrestrials or deities who have rational capacities (It seems likely that Kant recognized this when he wrote "man, and in general every rational being"). The serious problem is that many humans are not persons. Some members of humanity—i.e. infants, children, people with advanced forms of autism or Alzheimer's disease or other cognitive disorders—do not have the rational, self-reflective capacities associated with personhood. This problem, unfortunately known in the literature as the problem of "marginal humans," poses serious difficulties for "personhood" as the criterion of moral considerability. Many beings who's positive moral value we have deeply held intuitions about, and who we treat as morally considerable, will be excluded from consideration by this account.
There are three ways to respond to this counter-intuitive conclusion. One, which can be derived from one interpretation of Kant, is to suggest that non-persons are morally considerable indirectly. Though Kant believed that animals were mere things it appears he did not genuinely believe we could dispose of them any way we wanted. In the Lectures on Ethics he makes it clear that we have indirect duties to animals, duties that are not toward them, but in regard to them insofar as our treatment of them can affect our duties to persons.
If a man shoots his dog because the animal is no longer capable of service, he does not fail in his duty to the dog, for the dog cannot judge, but his act is inhuman and damages in himself that humanity which it is his duty to show towards mankind. If he is not to stifle his human feelings, he must practice kindness towards animals, for he who is cruel to animals becomes hard also in his dealings with men. (Kant, LE, 240)
And one could argue the same would be true of those human beings who are not persons. We disrespect our humanity when we act in inhuman ways towards non-persons, whatever their species.
But this is unsatisfying—it fails to capture the independent wrong that is being done to the non-person. When someone rapes a woman in a coma, or whips a severely brain damaged child, or sets a cat on fire, they are not simply disrespecting humanity or themselves as representatives of it, they are wronging these non-persons. So, a second way to avoid the counter-intuitive conclusion is to argue that such non-persons stand in the proper relations to "rational nature" such that they should be thought of as morally considerable. Allen Wood (1998) argues in this way and suggests that all beings that potentially have a rational nature, or who virtually have it, or who have had it, or who have part of it, or who have the necessary conditions of it, what he calls "the infrastructure of rational nature", should be directly morally considerable. Insofar as a being stands in this relation to rational nature, they are the kinds of beings that can be wronged.
This response is not unlike that of noted animal rights proponent, Tom Regan, who argues that what is important for moral consideration are not the differences between humans and non-humans but the similarities. Regan argues that because persons share with certain non-persons (which includes those humans and non-humans who have a certain level of organized cognitive function) the ability to be experiencing subject of a life and to have an individual welfare that matters to them regardless of what others might think, both deserve moral consideration. Regan argues that subjects of a life
want and prefer things, believe and feel things, recall and expect things. And all these dimensions of our life, including our pleasure and pain, our enjoyment and suffering, our satisfaction and frustration, our continued existence or our untimely death—all make a difference to the quality of our life as lived, as experienced, by us as individuals. As the same is true of … animals … they too must be viewed as the experiencing subjects of a life, with inherent value of their own. (Regan, 1985)
A third response is simply to reject rational nature as the touchstone of moral considerability. This is the kind of direct argument that utilitarians have traditionally made. They argue that the truly morally important feature of beings is unappreciated when we focus on personhood or the rational, self-reflective nature of humans, or the relation a being stands in to such nature, or being the subject of a life. What is really important, utilitarians maintain, is the promotion of happiness, or pleasure, or the satisfaction of interests, and the avoidance of pain, or suffering, or frustration of interests. Bentham, one of the more forceful defenders of this "sentientist" view of moral considerability, famously wrote:
Other animals, which, on account of their interests having been neglected by the insensibility of the ancient jurists, stand degraded into the class of things. [original emphasis] ... The day has been, I grieve it to say in many places it is not yet past, in which the greater part of the species, under the denomination of slaves, have been treated ... upon the same footing as ... animals are still. The day may come, when the rest of the animal creation may acquire those rights which never could have been withholden from them but by the hand of tyranny. The French have already discovered that the blackness of skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may come one day to be recognized, that the number of legs, the villosity of the skin, or the termination of the os sacrum, are reasons equally insufficient for abandoning a sensitive being to the same fate. What else is it that should trace the insuperable line? Is it the faculty of reason, or perhaps, the faculty for discourse?...the question is not, Can they reason? nor, Can they talk? but, Can they suffer? (Bentham 1781)
Contemporary utilitarians, such as Peter Singer (1990, 1993), suggest that there is no morally justifiable way to exclude from moral consideration non-humans or non-persons who can clearly suffer. Any being that has an interest in not suffering deserves to have that interest taken into account. And a non-human who acts to avoid pain can be thought to have just such an interest. Even contemporary Kantians have acknowledged the moral force of the experience of pain. Korsgaard, for example, writes "it is a pain to be in pain. And that is not a trivial fact" (1996, 154).
When you pity a suffering animal, it is because you are perceiving a reason. An animal's cries express pain, and they mean that there is a reason, a reason to change its conditions. And you can no more hear the cries of an animal as mere noise than you can the words of a person. Another animal can obligate you in exactly the same way another person can. …So of course we have obligations to animals. (Korsgaard, 1996, 153)
When we encounter an animal in pain we recognize their claim on us, and thus beings who can suffer are morally considerable.