Somatotype

The three somatotypes—endomorphic, mesomorphic, and ectomorphic—are basic classifications of animal body types according to the prominence of different basic tissues types, roughly: digestive, muscular, and nervous tissues. They form the core of a theory, developed in the 1940s by American psychologist William Sheldon, associating body types with human temperament types. This linkage is fairly simplistic and is seen as outdated in physiological science, but the account of somatotypes is still probably a valid, if limited way to sort basic body types.

á==Somatotype theory== Using anthropometric methods Sheldon studied the photographed bodies of some 4,000 men from front view, side view, and back view. He concluded that the physique of men can be divided into the contribution of three fundamental elements: the somatotypes. He named his somatotypes after the three germ layers of embryonic development: the endoderm, that develops into the digestive tract, the mesoderm, that is to become muscle, heart and blood vessels, and the ectoderm that is to form the nervous system. Sheldon’s “somatotypes” and their (presumed and supposed) associated psychological traits can be summarised as follows:
 * Ectomorphic body type is characterized by long arms and legs and a short upper body and narrow shoulders, and supposedly have a higher proportion of nervous tissue. They also have long and thin muscles. Ectomorphs usually have a very low fat storage; therefore they are usually referred to as slim.


 * Mesomorphic body type is characterized by a high rate of muscle growth and a higher proportion of muscular tissue. They have large bones, solid torso combined with low fat levels. It is also noted that they have wide shoulders with a narrow waist.
 * Endomorphic body type is characterized by an increased amount of fat storage, due to having a larger number of fat cells than the average person, as well as higher proportion of digestive tissue. They have a wide waist and a large bone structure.

In his book, Atlas of Men, Sheldon categorised all possible body types according to a scale ranging from 1 to 7 for each of the 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. Sheldon's research showed that a predisposition towards criminality might be influenced by a somatotype high in endomorphy and intermediate in mesomorphy, and in contrast, a predisposition towards suicidality might be influenced by a somatotype high in ectomorphy; on the other hand, ectomorphs were found to be more common in mental institutions.

Modern assessments
Some of this is useful in general and human biology, if weak behavioral science. Advanced triploblastic animals, such as mammals, or modern humans in particular, do have these three basic ...

Changing somatotypes
The three body type descriptions could be explained as differences in body composition, which can be altered by specific diets and training techniques.

After a period of significant weight loss, a person who was once considered an endomorph may begin to instead resemble an ectomorph. Likewise, an athletic mesomorph may begin to look more like an endomorph as he ages and loses muscle mass.

However, some aspects of the Somatotype cannot be changed, for example, a characteristic of an endomorphic body type is wide shoulders as well as a wide waist. Ectomorphs may have narrower shoulders and slimmer waists. Although, muscle and adipose mass can be changed, the bone structures associated with endomorphs, ectomorphs and mesomorphs means completely changing between two somatotypes is not always possible.

Sheldon's body types in popular culture

 * The Chipmunk characters Alvin (mesomorph), Simon (ectomorph), and Theodore (endomorph) adhere strongly to Sheldon’s types in both mind and body.
 * In "Weird Al" Yankovic's song, "Wanna B Ur Lovr", one of his pickup lines is "I like your skeletal structure, baby, you're an ectomorph no doubt".

Arguments against somatotypes
In July 2006, a study contradicted this stereotype, indicating that obese individuals in the United States were more likely to have been diagnosed with depression, bipolar disorder, and panic disorder/agoraphobia (PMID 16818872). However, the United States is known to have the biggest proportion of obese people in the world – which does not indicate a higher number of endomorphs but rather a higher number of people with eating disorders. A lack of food in other countries can also go hand-in-hand with a lower proportion of obese people. Anyone can become fat – even an ectomorph – and being fat is not the same as 'being endomorphic'; therefore the disorders above merely illuminate disorders that cause, are caused by or can go hand-in-hand with eating disorders.

Defense of Sheldon by supporters
The words endomorphic, mesomorphic and ectomorphic are still sometimes used to describe body types, maybe especially in association with weight training aimed at gaining muscle. In some types of New Age there is an interest in this kind of correlation between physiology and psyche, but the majority of scientists today generally consider these theories from the 1930s and 1940s outdated. Sheldon's theories arose during World War II and some saw in the somatotypes a link to the Nazi ideology of genetic cleansing and racial hygiene. After World War II, interest in studying inborn temperament was quickly rejected as anti-democractic, or worse. Sheldon's 4,000 photographs of nude Yale undergraduates were destroyed. 

Sheldon's ideas were not original but a variation on an old idea, beginning with Aristotle's concept of the "vegetative soul". Harvard psychologist Jerome Kagan has convincingly shown the existence of inborn temperament across diverse cultures, linking cardinal traits to neurochemical activation patterns involving the autonomic nervous system. Antonio Damasio's theory of frontal lobe function, the somatic markers hypothesis, posits goal directed behavior as primarily directed by heavy somatosensory input from the internal milieu. It is not a large leap to consider a role for different patterns of somatosensory input in persons with different body types.