It's not that there are no differences between human and non-human animals, any more than there are no differences between black people and white people, freeborn citizens and slaves, men and women, Jews and gentiles, gays or heterosexuals. The question is rather: are they morally relevant differences? This matters because morally catastrophic consequences can ensue when we latch on to a real but morally irrelevant difference between sentient beings.

If a curiously selective plague came along and killed all people of intermediate height, 'tall' and 'short' would come to have just as precise a meaning as 'bird' or 'mammal'. The same is true of human ethics and law. Our legal and moral systems are deeply species-bound. The director of a zoo is legally entitled to 'put down' a chimpanzee that is surplus to requirements, while any suggestion that he might 'put down' a redundant keeper or ticket-seller would be greeted with howls of incredulous outrage. The chimpanzee is the property of the zoo. Humans are nowadays not supposed to be anybody's property, yet the rationale for discriminating against chimpanzees in this way is seldom spelled out, and I doubt if there is a defensible rationale at all. Such is the breathtaking speciesism of our attitudes, the abortion of a single human zygote can arouse more moral solicitude and righteous indignation than the vivisection of any number of intelligent adult chimpanzees! [T]he only reason we can be comfortable with such a double standard is that the intermediates between humans and chimps are all dead.

Since Darwin, scientists have agreed that there is no ‘magical’ essential difference between human and other animals, biologically-speaking. Why then do we make an almost total distinction morally? If all organisms are on one physical continuum, then we should also be on the same moral continuum. … The only arguments in favour of painful experiments on animals are: 1) that the advancement of knowledge justifies all evils – well does it? 2) that possible benefits for our own species justify mistreatment of other species – this may be a fairly strong argument when it applies to experiments where the chances of suffering are minimal and the probability of aiding applied medicine is great, but even so it is still just ‘speciesism’, and as such it is a selfish emotional argument rather than a reasoned one.

When it comes to respecting someone, it is completely irrelevant whether that being can speak, whether she can think in the same way we do, or whether we have some kind of special relation with her. Because that isn't what determines whether she can be harmed or benefited by our actions. The relevant point is whether she can feel suffering or/and joy. Furthermore, if that was the case, many humans should be discriminated against too. Because there are many humans who can't talk or can't think as other humans do, and many have no one who cares for them. So if the arguments that are used to discriminate against animals were accepted, we should also discriminate against humans. These are some general arguments that are seldom used. I don't understand why not. Because debating these points, debating these issues is what will eventually lead society to a change. Of course there are other arguments involved and there are many other ways to question speciesism. My main point is we should be focused on challenging it.

Man is the "ethical animal" — ethical in potentiality even if, unfortunately, not in actuality. His capacity for ethical judgment — like freedom, reason and the other unique characteristics of the human being — is based upon his consciousness of himself.

In what terms should we think of these beings, nonhuman yet possessing so very many human-like characteristics? How should we treat them? Surely we should treat them with the same consideration and kindness as we show to other humans; and as we recognize human rights, so too should we recognize the rights of the great apes? Yes.

I conceive two species of inequality among men; one which I call natural, or physical inequality, because it is established by nature, and consists in the difference of age, health, bodily strength, and the qualities of the mind, or of the soul; the other which may be termed moral, or political inequality, because it depends on a kind of convention, and is established, or at least authorized, by the common consent of mankind. This species of inequality consists in the different privileges, which some men enjoy, to the prejudice of others, such as that of being richer, more honoured, more powerful, and even that of exacting obedience from them.

Animal liberationists do not separate out the human animal, so there is no rational basis for saying that a human being has special rights. A rat is a pig is a dog is a boy. They are all mammals

Animals no doubt have different interests from humans, and may experience different pleasures and pains, but the principle of equal consideration for similar interests still holds, and pleasures and pains of similar intensity and duration should be given equal weight, whether they are experienced by humans or by animals.

What exactly is the minority moral position for which members of a gathering such as this are likely to be propagandists? It will certainly differ slightly from person to person. There is, however, one rather minimal principle to which I trust that all here would assent, namely that the suffering or frustration of an animal of another species is an evil of the same general sort as is the suffering or frustration of a human being, and that we humans have the same general sort of moral obligation to refrain from causing, and to try actively to prevent, such evil when it concerns animals as when it concerns human beings.

Mother, recently I have discovered the one way in which human beings differ completely from other animals. Man has, I know, language, knowledge, principles, and social order, but don't all the other animals have them too, granted the difference of degree? Perhaps the animals even have religions. Man boasts of being the lord of all creation, but it would seem as if essentially he does not differ in the least from other animals. But, Mother, there was one way I thought of. Perhaps you won't understand. It's a faculty absolutely unique to man - having secrets. Can you see what I mean?

What right have humans to impose our values on members of another race or species? The charge is seductive but misplaced. There is no anthropomorphism here, no imposition of human values on alien minds. Human and nonhuman animals are alike in an ethically critical respect. The pleasure-pain axis is universal to sentient life. No sentient being wants to be harmed – to be asphyxiated, dismembered, or eaten alive. The wishes of a terrified toddler or a fleeing zebra to flourish unmolested are not open to doubt even in the absence of the verbal capacity to say so.

Or, si l’on compare la diversité prodigieuse d’éducations et de genres de vie qui règne dans les différents ordres de l’état civil, avec la simplicité et l’uniformité de la vie animale et sauvage, où tous se nourrissent des mêmes aliments, vivent de la même manière, et font exactement les mêmes choses, on comprendra combien la différence d’homme à homme doit être moindre dans l’état de nature que dans celui de société, et combien l’inégalité naturelle doit augmenter dans l’espèce humaine par l’inégalité d’institution.

It is commonly believed that animal ethics entails respect for natural processes, because nonhuman animals are able to live relatively easy and happy lives in the wild. However, this assumption is wrong. Due to the most widespread reproductive strategy in nature, r-selection, the overwhelming majority of nonhuman animals die shortly after they come into existence. They starve or are eaten alive, which means their suffering vastly outweighs their happiness. Hence, concern for nonhuman animals entails that we should try to intervene in nature to reduce the enormous amount of harm they suffer. Even if this conclusion may seem extremely counter-intuitive at first, it can only be rejected from a speciesist viewpoint.