From Wikipedia about Peter Singer:
"
Animal Liberation (originally
published in 1975, second edition 1990, third edition 2002) was a major formative influence on the modern
animal rights movement. Although Singer rejects rights as a moral ideal independent from his utilitarianism based on interests, he accepts rights as derived from utilitarian principles, particularly the principle of minimizing suffering. (Compare his fellow utilitarian
John Stuart Mill, whose defense of the rights of the individual in
On Liberty is introduced with the qualification, "It is proper to state that I forego any advantage which could be derived to my argument from the idea of abstract right as a thing independent of utility"). Singer allows that animal rights are not exactly the same as human rights, writing in
Animal Liberation that "[T]here are obviously important differences between human and other animals, and these differences must give rise to some differences in the rights that each have." So, for example an animal does not have the right to a good education as this is meaningless to them, just as a man does not have the right to an abortion. But he is no more skeptical of animal rights than of the rights of women, beginning
Animal Liberation by defending just such a comparison against
Mary Wollstonecraft's 18th-century critic
Thomas Taylor, who argued that if Wollstonecraft's reasoning in defense of women's rights were correct, then "brutes" would have rights too. Taylor thought he had revealed a
reductio ad absurdum of Wollstonecraft's view; Singer regards it as a sound logical implication. Taylor's
modus tollens is Singer's
modus ponens.
In
Animal Liberation, Singer argues against what he calls
speciesism:
discrimination on the grounds that a being belongs to a certain species. He holds the interests of all beings capable of suffering to be worthy of
equal consideration, and that giving lesser consideration to beings based on their having wings or fur is no more justified than discrimination based on skin color. In particular, he argues that while animals show lower intelligence than the average human, many severely retarded humans show equally diminished mental capacity, and intelligence therefore does not provide a basis for providing nonhuman animals any less consideration than such retarded humans. He concludes that the use of animals for food is unjustifiable because it creates unnecessary suffering, and considers
veganism the most fully justifiable diet. Singer also condemns most
vivisection, though he believes a few animal experiments may be acceptable if the benefit (in terms of improved medical treatment, etc.) outweighs the harm done to the animals used. Due to the subjectivity of the term "benefit", controversy exists about this and other utilitarian views. But he is clear enough that humans of comparable sentience should also be candidates for any animal experimentation that passes the benefit test. So a monkey and a human infant would be equally available for the experiment, from a moral point of view, other things being equal. If performing the experiment on the infant isn't justifiable, then Singer believes that the experiment shouldn't happen at all -- instead, the researchers should pursue their goals using computer simulations or other methods. Acceptable vivisection would be weakly "speciesist" insofar as it passes over human candidates for non-human subjects, but arguably species membership in such cases would be a legitimate tie-breaking consideration."