Down \ˈdau̇n\ (audio pronunciation) John Langdon Haydon (1828–1896),
British physician. Down published in 1866 a treatise on the degeneration of race as a result of marriages of consanguinity. He classified individuals exhibiting mental retardation according to the supposed physiognomic features of various races including the American Indian, Caucasian, Ethiopian, and Mongolian. His classification was invalid, but one kind of moderate to severe mental retardation came to be known as mongolism, although it is now called Down syndrome or Down's syndrome.