Lionel Penrose was a brilliant medical geneticist whose definitive study the Colchester Report (1938) refuted the current view that high grade mental defect followed Mendelian laws of inheritance. As a Quaker, Penrose deeply sympathised with the mentally handicapped and opposed current campaigns in Britain for their sterilisation. He wrote in 1934:

“If, in each generation, it were possible tp prevent all the defectives from breeding, mental deficiency would not be exterminated. The incidence would only be reduced by one-eleventh every thirty years…Generally speaking, it is unwise to be unduly optimistic about the results of eugenic measures in medicine”:

The Influence of Heredity on Disease.