Speciesism is the assigning of different value to beings according to their species membership. The term was coined by psychologist Richard D. Ryder in 1973 to denote a prejudice against non-humans.
"I use the word 'speciesism'," he wrote in 1975, "to describe the widespread discrimination that is practised by man against other species ... Speciesism is discrimination, and like all discrimination it overlooks or underestimates the similarities between the discriminator and those discriminated against."
As Peter Singer, the populariser of the term speciesism, says, speciesism follows logically from a utilitarian conception of equality:
"It is an implication of this principle of equality that our concern for others ought not to depend on what they are like, or what abilities they possess - 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 the case against racism and the case against sexism must both ultimately rest; and it is in accordance with this principle that speciesism is also to be condemned. If possessing a higher degree of intelligence does not entitle one human being to use another for its own ends, how can it entitle human beings to exploit nonhuman beings?"
This essential point is captured by Bentham's famous passage:
“Other animals, which, on account of their interests having been neglected by the insensibility of the ancient jurists, stand degraded into the class of things. ... The day has been, I grieve it to say in many places it is not yet past, in which the greater part of the species, under the denomination of slaves, have been treated ... upon the same footing as ... animals are still. 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 skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may come one day to be recognized, that the number of 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 for discourse?...the question is not, Can they reason? nor, Can they talk? but, Can they suffer? Why should the law refuse its protection to any sensitive being?... The time will come when humanity will extend its mantle over everything which breathes”
Richard Dawkins briefly reviewed arguments that treat humans as better than other animals and presented family trees of apes to support his claim that humans are African great apes. He argued that there is no biological justification for treating humans differently from other great apes: "There is no natural category that includes chimpanzees, gorillas and orangutans but excludes humans." 
- ↑ Ryder, Richard. "All beings that feel pain deserve human rights", The Guardian, August 6, 2005.
- ↑ Singer, Peter  Animal Rights and Human Obligations, New Jersey, 1989, pp. 148-162
- ↑ Bentham, Jeremy. Principles of Morals and Legislation Summary, full text of Introduction to the Principles of Morals and Legislation, second edition, 1823, chapter 17, footnote.
- ↑ Dawkins, Richard "Gaps in the Mind," in Paola Cavalieri & Peter Singer (eds.), The Great Ape Project. New York: St. Martin's Griffin, 1993, pp. 81-87