Complex sentence: Constitutional theories in psychology (e.g., Sheldon, Kretschmer) emphasize the relationship between body structure and temperament ever since Hippocrates thought that body structure goes hand in hand with the temperament and susceptibility to certain diseases.
Split into simpler sentences: Constitutional theories in psychology (e.g., Sheldon, Kretschmer) emphasize the relationship between body structure and temperament. These theories have been around since Hippocrates thought that body structure goes hand in hand with the temperament and susceptibility to certain diseases.