An excerp from Practical Ethics 1993 Peter Singer The argument for extending the principle of equality beyond our own species is simple, so simple that it amounts to no more than a clear understanding of the nature of the principle of equal consideration of interests.... [T]his principle implies that our concern for others ought not to depend on what they are like, or what abilities they posses (although precisely what this concern requires us to do may vary according to the characteristics of those affected by what we do). It is on this basis that we are able to say that the fact that some people are not members of our race does not entitle us to exploit them, and similarly the fact that some people are less intelligent than others does not mean that their interests may be disregarded. But the principle also implies that the fact that beings are not members of our species does not entitle us to exploit them, and similarly the fact that other animals are less intelligent thanwe are does not mean that their interests may be disregarded. ... Many philosophers have advocated equal consideration of interests, in some form or other, as a basic moral principle. Few recognized that the principle has applications beyond our own species. One of the few who did was Jeremy Bentham, the founding father of modern utilitarianism. In a forwardlooking passage, written at a time when black slaves in the British dominions were still being treated much as we now treat nonhuman animals, Bentham wrote: 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 the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may one day come to be recognised that the number of the 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 of discourse? But a full-grown horse or dog is beyond comparison a more rational, as well as a more conversable, animal than an infant of a day, or a week, or even a month, old. But suppose they were otherwise, what would it avail? The question is not, Can they reason? nor Can they talk? but, Can they suffer?' In this passage Bentham points to the capacity for suffering as the vital characteristic that entitles a being to equal consideration. The capacity for suffering-or more strictly, for suffering and/or enjoyment or happiness-is not just another characteristic like the capacity for language, or for higher mathematics. Bentham is not saying that those who try to mark `the insuperable line' that determines whether the interests of a being should be considered happen to have selected the wrong characteristic. The capacity for suffering and enjoying things is a prerequisite for having interests at all, a condition that must be satisfied before we can speak of interests in any meaningful way. It would be nonsense to say that it was not in the interests of a stone to be kicked along the road by a schoolboy. A stone does not have interests because it cannot suffer. Nothing that we can do to it could possibly make any difference to its welfare. A mouse, on the other hand, does have an interest in not being tormented, because it will suffer if it is.If a being suffers, there can be no moral justification for refusing to take that suffering into consideration. No matter what the nature of the being, the principle of equality requires that its suffering be counted equally with the like suffering-in so far as rough comparisons can be made-of any other being. If a being is not capable of suffering, or of experiencing enjoyment or happiness, there is nothing to be taken into account. This is why the limit of sentience (using the term as a convenient, if not strictly accurate, shorthand for the capacity to suffer or experience enjoyment or happiness) is the only defensible boundary of concern for the interests of others. To mark this boundary by some characteristic like intelligence or rationality would be to mark it in an arbitrary way. Why not choose some other characteristic, like skin colour? Racists violate the principle of equality by giving greater weight to the interests of members of their own race when there is a clash between their interests and the interests of those of another race. White racists do not accept that pain is as bad when it is felt by blacks as when it is felt by whites. Similarly those I would call 'speciesists' give greater weight to the interests of members of their own species when there is a clash between their interests and the interests of those of other species. Human speciesists do not accept that pain is as bad when it is felt by pigs or mice as when it is felt by humans. That, then, is really the whole of the argument for extending the principle of equality to nonhuman animals; but there may be some doubts about what this equality amounts to in practice. In particular, the last sentence of the previous paragraph may prompt some people to reply: `Surely pain felt by a mouse just is not as bad as pain felt by a human. Humans have much greater awareness of what is happening to them, and this makes their suffering worse. You can't equate the suffering of, say, a person dying slowly from cancer, and a laboratory mouse undergoing the same fate.' I fully accept that in the case described the human cancer victim normally suffers more than the nonhuman cancer victim. This in no way undermines the extension of equal consideration of interests to nonhumans. It means, rather, that we must take care when we compare the interests of different species. In some situations a member of one species will suffer more than a member of another species. In this case we should still apply the principle of equal consideration of interests but the result of so doing is, of course, to give priority to relieving the greater suffering. The Bentham quote is from J. Bentham, Introduction to the Principles of Morals and Legislation (1789; New York: Hafner, 1948),