To classify people on the basis of their skin, their intelligence, or some other quality that is perceived as inborn. This urge is quite ancient. According to Greek philosopher Plato, his teacher Socrates proposed that, in the ideal state, people would be raised from birth to believe that their social system reflected an inborn biological order.
Racial theories emerged during the 19th century in the United States as a justification for the enslavement of African Americans. Southern theorists sought a Natural law justification that would defend the institution of black slavery as an outgrowth of the supposed “natural inferiority” of Africans. They drew on the concept of “biological determinism” the idea that social and economic distinctions in society are inherited and inborn rather than learned. Biological determinists sought scientific justification of the differences between human races. People at the bottom of the social level, biological determinists argued, were at the bottom because they were innately inferior. Many famous 19th-century United States statesmen, including Thomas Jefferson and Abraham Lincoln, adhered to this view.