Somatotype and constitutional psychology

Somatotype is a taxonomy developed in the 1940s, by American psychologist William Herbert Sheldon, to categorize the human physique according to the relative contribution of three fundamental elements, somatotypes, named after the three germ layers of embryonic development: the endoderm, (develops into the digestive tract), the mesoderm, (becomes muscle, heart and blood vessels), and the ectoderm (forms the skin and nervous system). His initial visual methodology has been discounted as subjective, but later formulaic variations of the methodology, developed by his original research assistant Barbara Heath, and later Lindsay Carter and Rob Rempel are still in academic use.

Constitutional psychology is a now neglected theory, also developed by Sheldon in the 1940s, which attempted to associate his somatotype classifications with human temperament types. The foundation of these ideas originated with Francis Galton and eugenics. Sheldon and Earnest Hooton were seen as leaders of a school of thought, popular in anthropology at the time, which held that the size and shape of a person's body indicated intelligence, moral worth and future achievement.

In his 1954 book, Atlas of Men, Sheldon categorised all possible body types according to a scale ranging from 1 to 7 for each of the three "somatotypes", where the pure "endomorph" is 7–1–1, the pure "mesomorph" 1–7–1 and the pure "ectomorph" scores 1–1–7. From type number, an individual's mental characteristics could supposedly be predicted. Barbara Honeyman Heath, who was Sheldon's main assistant in compiling Atlas of Men, accused him of falsifying the data he used in writing the book.

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