the theory that every person possesses some degree of three primary temperamental components that relate to three basic body builds (somatotypes), measured on a 7-point scale. The three body types—ectomorph, endomorph, and mesomorph—are correlated with the three components of temperament: cerebrotonia, viscerotonia, and somatotonia. Constitution provides a substructure, but nutrition and early experiences also influence the physique and temperament, respectively. [William H. Sheldon (1899–1970), U.S. psychologist]
a group of theories that describe aging as resulting from genetic encoding within an individual’s DNA whereby one is born with a predetermined tendency toward a developmental timetable. Also called planned obsolescence theory. Compare variable rate theory.