Most of us believe that we are entitled to treat members of other species in ways which would be considered wrong if inflicted on members of our own species. We kill them for food, keep them confined, use them in painful experiments. The moral philosopher has to ask what relevant difference justifies this difference in treatment. A look at this question will lead us to re-examine the distinctions which we have assumed make a moral difference. It has been suggested by Peter Singer 1 that our current attitudes are "speciesist," a word intended to make one think of "racist" or "sexist." The idea is that membership in a species is in itself not relevant to moral treatment, and that much of our behavior and attitudes towards nonhuman animals is based simply on this irrelevant fact. There is, however, an important difference between racism or sexism and "speciesism." We do not subject animals to different moral treatment simply because they have fur and feathers, but because they are in fact different from human beings in ways that could be morally relevant.
It is false that women are incapable of being benefited by education, and therefore that claim cannot serve to justify preventing them from attending school. But this is not false of cows and dogs, even chimpanzees. Intelligence is thought to be a morally relevant capacity because of its relation to the capacity for moral responsibility. What is Singer's response He agrees that nonhuman animals lack certain capacities that human animals possess, and that this may justify different treatment. But it does not justify giving less consideration to their needs and interests.
According to Singer, the moral mistake which the racist or sexist makes is not essentially the factual error of thinking that blacks or women are inferior to white men. For even if there were n factual error, even if it were true that blacks and women are less intelligent and responsible than whites and men, this would not justify giving less consideration to their needs and interests. It is important to note that the term "speciesism" is in one way like, and in another way unlike, the terms "racism" and "sexism." What the term "speciesism" has in common with these terms is the reference to focusing on a characteristic which is, in itself, irrelevant to moral treatment. And it is worth reminding us of this.
But Singer's real aim is to bring us to a new understanding of the idea of equality. The question is, on what do claims to equality rest The demand for human equality is a demand that the interests of all human beings be considered equally, unless there is a moral justification for not doing so. But why should the interests of all human beings be considered equally In order to answer this question, we have to give some sense to the phrase, "All men (human beings) are created equal.".