Even if we ourselves are not personally scandalized by the notion of other animals as close relatives, even if our age has accommodated to the idea, the passionate resistance of so many of us, in so many epochs and cultures, and by so many distinguished scholars, must say something important about us. What can we learn about ourselves from an apparent error so widespread, propagated by so many leading philosophers and scientists, both ancient and modern, with such assurance and self-satisfaction? One of several possible answers: A sharp distinction between humans and "animals" is essential if we are to bend them to our will, make them work for us, wear them, eat them--without any disquieting tinges of guilt or regret. With untroubled consciences, we can render whole species extinct--for our perceived short-term benefit, or even through simple carelessness. Their loss is of little import: Those beings, we tell ourselves, are not like us. An unbridgeable gap gas thus a practical role to play beyond the mere stroking of human egos. Darwin's formulation of this answer was: "Animals whom we have made our slaves, we do not like to consider our equals.
Carl Sagan, Shadows of Forgotten Ancestors
animals, speciesism