Speciesism is a term found primarily in the literature dealing with animal rights. It is used in a derogatory fashion to designate a bias or prejudice analogous to racism or sexism. In speciesism, the bias is in favor of the fundamental interests of humans as opposed to those of nonhumans. A “speciesist” would be someone who favors and demonstrates partiality toward humans over animals and who believes that humans have special traits that animals lack (reason, language, technological skills, etc.), thereby making them superior and more important beings. In this way, speciesism can be seen to be a product of a strong anthropocentrism that holds humans to be the focus of and purpose for the universe.

The first expression and use of the term speciesism in a formal way came in 1970 when clinical psychologist Richard Ryder of Oxford University used the term in a leaflet that he had privately printed about the abuses of animal experimentation and animal abuse. Ryder reported that the term came to him while he was taking a bath and contemplating the way humans treat animals. Since Darwin had shown that humans too are animals, Ryder thought that speciesism was just like racism and sexism—a form of prejudice based on morally irrelevant physical differences. We can find more extended arguments about speciesism in the writings of animal rights advocates such as Australian ethicist Peter Singer. Singer is known as a “preference utilitarian,” which means that morally correct action produces the most satisfaction of preferences. But, with respect to animals, Singer holds that they, just like humans, have such preferences or interests and that it would be a moral mistake to overlook their interests even though most people do. The mistake of not granting equal moral  consideration to the interests of animals is a form of speciesism according to Singer. An even more egregious form of it would be to give the interests of human beings preference over those of other beings merely because the former interests are those of a human being. Hence, for Singer, it is more appropriate to treat all beings as individuals and not as members of a species.

The issue of animal experimentation in medicine is one that is often pointed to as being biased by speciesism. Animal rights advocates hold that animal experimentation in medicine is morally objectionable and should be discontinued. They argue that just because animal experimentation may lead to advances in medicine and this might be beneficial to humans, such benefit is no good reason to put animals in situations that cause them great pain and suffering as is the case with medical experimentation done on them. The claim that beneficial outcomes for humans is the result of such experimentation and therefore justification enough to continue the practice is nothing more than prejudice in favor of humans because they are humans, that is, a form of speciesism, in the eyes of animal liberationists.