The belief that fat people are jolly and skinny people are shy and introverted is very common, even though there are many exceptions. Where did these assumptions come from?
The relation between physique and personality was the work of psychologist and physician, William H. Sheldon. His somatotype theory evolved from knowledge about the embryonic development in the womb. Shortly after conception, the unborn child is merely a hollow ball of cells arranged in three layers — endoderm, mesoderm and ectoderm.
The endoderm — the innermost layer — gradually develops into the stomach, intestines, heart, lungs and etceteras. The middle layer — the mesoderm — becomes muscles and bones. The ectoderm — the outer layer — evolves into the skin, hair, nails and nervous system. If one of these layers has a greater influence on the child's development, it will determine the child's body build — endomorph, mesomorph or ectomorph — and the personality that goes with it. (By the way, "morph" means "form.")
Sheldon developed methods of measuring various body dimensions and rating these dimensions on a 7-point scale. Each person would have a code indicating the ratings on each of the three components. For example, a "4-6-1" person would be average in endomorphy, high in mesomorphy and low in ectomorphy.
To better understand what this code means, we need to examine the extremes in each component. An extreme endomorph (7-1-1) is best typified by Santa Claus — with or without the beard. Since the endoderm dominates, the "gut" is the predominant feature. (He is a "fatty.") The personality characteristics that go along with the endomorph include loving comfort and sociability, with strong needs for food, people and affection. The endomorph is typically relaxed, even-tempered, tolerant and easy-going.
In contrast, the extreme mesomorph (1-7-1) — with a preponderance of bone and muscle — looks like the football lineman or the comic book character, "the Hulk." This type of person is adventuresome, loving risk-taking and vigorous physical activity. He would also tend to be aggressive, dominant, courageous, noisy, and callous toward the feelings of others.
The third type — the extreme ectomorph (1-1-7) — is very tall and thin. In relation to his body volume, he has more skin. (That is why we call this type "skinny.") If you have seen Walt Disney's cartoon version of "Legend of Sleepy Hollow," the Ichabod Crane character is an example of this body shape. Don Knotts from "Three's Company" and "Mayberry RFD" fame is another example of an ectomorph. Their personalities tend to be restrained and inhibited, preferring solitude, avoiding attention, and being self-conscious, aloof and afraid of people.
However, most people are not at these extremes. They exhibit a combination of both the body types and the personality traits. For example, the idealized woman would probably be a 3-42. Although muscular (mesomorphic) tendencies would be evident, she still would have the curves (endomorphic) that many men want a woman to have. In contrast, I am a 5-4-2, what Sheldon laughingly called the "pyknic practical joke." In adolescence and early adulthood, mesomorphic aspects predominate. However, as aging proceeds, the chest drops down to the waistline as endomorphic tendencies accumulate.
Sheldon's theory helps to predict your personality from your body type — if you are at one of the extremes. On the other hand, it is hard to predict your personality traits, if you only have moderate amounts of each body type (4-3-4 or 3-4-3). If you only have some of the personality traits related to each body type, which ones will you have?
The theory also does not tell which factor causes which. Do people become muscular, because they exercise? Or do people engage in physical activity more, because their body type makes them more capable of doing so? Do fat people love food, or has loving food made them fat? Like so many other theories, Sheldon's somatotype theory raises more questions than it answers.
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