Somatotype and Constitutional Psychology

Somatotype is a theory proposed in the 1940s by the American psychologist William Herbert Sheldon to categorize the human physique by the relative contribution of three elements he named somatotypes, ectomorphic, mesomorphic and endomorphic, terms he borrowed from the three germ layers of embryonic development: the endoderm that becomes the digestive tract, the mesoderm that becomes muscle, heart and blood vessels, and the ectoderm that forms the skin and nervous system. Constitutional psychology, a related theory Sheldon developed in the same decade, attempted to link his somatotype classifications to human temperament types, building on ideas that trace back to Francis Galton and eugenics; Sheldon and Earnest Hooton led a school of thought, popular in anthropology at the time, that held the size and shape of a person's body could indicate their intelligence, moral worth and future achievement. In his 1954 book Atlas of Men, Sheldon rated every possible body type on a scale of 1 to 7 across the three somatotypes and claimed an individual's mental characteristics could be predicted from that rating; extending a pseudoscientific line of thought in criminology descended from Cesare Lombroso's theory of phrenology, Sheldon contended that criminals tended to be mesomorphic. The system remains in limited use today within physical education and cosmetology, and later researchers, including Sheldon's own original research assistant Barbara Heath and later Lindsay Carter and Rob Rempel, developed variations on his original categories.