In the 1940s, American psychologist, William Herbert Sheldon, developed an interesting theory by associating body types with human temperament types. Sheldon proposed that the human physique can be classified according to the relative contribution of three fundamental elements. He called them somatotypes, after the three germ layers of embryonic development: the endoderm, which develops into the digestive tract; the mesoderm, which develops into muscle, heart, and blood vessels; and the ectoderm, which forms the skin and nervous system .
Ectomorphic type is characterized by long, thin muscles and limbs, and low fat storage—usually referred to as slim. Ectomorphs are not predisposed to store fat or build muscle. The mesomorphic type is characterized by medium bones, solid torso, low fat levels, and wide shoulders, with a narrow waist—usually referred to as muscular. Mesomorphs are predisposed to build muscle, but not store fat. The endomorphic type is characterized by increased fat storage, a wide waist, and large bone structure, usually referred to as fat. Endomorphs are predisposed to store fat.
Sheldon’s method of somatotyping was modified by American anthropologists Barbara Heath and Lindsay Carter, based on several tools for precise quantification of shape and composition of human body. The somatotyping is done with anthropometric and photographic methods. The scores of relative endomorphy, mesomorphy, and ectomorphy are calculated based on standard tables and preset equations.
There is evidence that different physiques carry cultural stereotypes. For example, endomorphs are likely to be perceived as slow, sloppy, and lazy. Mesomorphs, in contrast, are typically popular, and hardworking, whereas ectomorphs are often viewed as intelligent, but fearful.
The body type descriptions could be modulated by body composition. Certain diets, exercises, and training techniques may have a role in modulating body compositions. During starvation, an endomorph may resemble an ectomorph, while an athletic mesomorph may look like an endomorph as a result of loss of muscle, and adipose mass, or simply due to the aging process. However, certain characteristics of the somatotype cannot be changed. For example, the bone structure is a fixed characteristic, except for a few changes due to the reduction in the distance between joints due to aging or physical deformities. Even cultural conditions may lead to a tendency to change temperaments. Because of many such limitations, the constitutional psychology approach was not accepted by the scientific world, and is not in use much today. During Sheldon’s time, Western scientists generally may have been aware about the various Eastern traditional ways in which people are classified for the purpose of treatments. If Sheldon would have visited India, or had studied concept of Prakriti in Ayurveda, perhaps constitutional psychology would have gone on a different route. An eminent physician–scientist from India, R. D. Lele has found a correlation of somatotypes with Prakriti, where he links mesomorphs to Kapha, endomorphs to Pitta, and ectomorphs to Vata types. Sheldon’s classification might serve as a basis for Prakriti assessment.