Leon J. Kamin (born December 29, 1927 in Taunton, Massachusetts) is an American psychologist who chaired Princeton University's Department of Psychology in 1968.
Kamin's initial contribution to psychology came from his research and documentation of the "blocking effect" (1969). He demonstrated that an animal is "blocked" from associating a stimulus (say, a bell) with result (say, food), if the stimulus is presented simultaneously with another stimulus that the animal already associates with the result. If the dog already associates the whistle with food, then sounding the whistle and ringing a bell when you give it food will not teach it to associate the bell with food. The blocking effect is one of the hallmark effects in the study of associative learning in humans and animals.
Kamin has long opposed the idea that significant personal traits are largely heritable. He became skeptical of the claims of Cyril Burt regarding the heritability of IQ, and published his findings in a 1974 book The Science and Politics of IQ. He co-authored the controversial book Not in Our Genes (1984) with geneticist Richard Lewontin and neurobiologist Steven Rose. This book, championing the "radical science movement," attacked sociobiology and evolutionary psychology. Kamin is known in some circles for his position that the heritability of IQ could be zero (Mackintosh, 1998) He is honorary professor of psychology at the University of Cape Town in South Africa.