"eugenicists made a mess of traits like intelligence. They were obsessed with splitting people into two categories--healthy and feebleminded--and then they would cast the feebleminded as a "class of vast and dangerous dimensions." Penrose saw intelligence as a far more complex trait. He likened intelligence to height: In every population, most people were close to average height, but some people were taller and shorter than average. Just being short wasn't equivalent to having some kind of a height disease. Likewise, people developed a range of different mental aptitudes."