Much of Dr. William Sheldon's professional life was devoted to investigating the range human personality traits or temperament types. Dr. Sheldon was particularly active in which field of study during the 1940s and eventually came to hold that there were three major human personality traits which he called Viscerotonia, Somatotonia, and Cerebrotonia. These personality traits, Sheldon came to believe, bore a direct relationship with each of three human body types ( or Somatypes ) which he called Endomorphy, Mesomorphy and Ectomorphy.