Singer, P. 1975. Animal Liberation - A New Ethics for Our Treatment of Animals. Avon Books, New York, NY.

The researcher's central dilemma exists in an especially acute form in psychology: either the animal is not like us, in which case there is no reason for performing the experiment; or else the animal is like us, in which case we ought not to perform an experiment ... which would be considered outrageous if performed on one of us. (p. 47).