The enduring characteristics of an individual's behavior, attitude, and feelings in everyday social situations make up personality. There are many influences on anindividual's personality, including culture, genetic makeup, and early family life. Studieshave shown that people with certain personality characteristics are more suitable forspecific occupations or special activities. Personality studies can also reveal therelationship between specific types of personalities and the incidence of disease, divorce,and stress-related problems. There are many different theories concerning the nature and development ofpersonality and the causes of personality changes. The ancient Greek physicianHippocrates believed that people behave differently because they have a predominance ofone type of bodily fluid, or humor. According to this theory, people with calm or passivepersonalities have one dominant humor, while impulsive and temperamental people have adifferent dominant humor. In the 20th century, other classification schemes wereadvanced. The German psychiatrist Ernst Kretschmer thought that personality wasdetermined by the person's body type--such as plump, lean, or athletic. He suggested thatshort persons were more likely to be social, friendly, and lively. Both of these theoriesremain unproven. Major advances have been made through behavioral genetics, the fieldconcerned with the relative influence of genetic and environmental factors on individualbehavior. One approach is to study the personalities of identical (monozygotic) twins whohave been separated since birth. Such individuals have the same genetic makeup but differin the environments in which they are reared. In a related method of study, thepersonalities of individuals who are adopted from birth are compared to the personalitiesof their adoptive and biological parents. These individuals have genetic material differentfrom that of their adoptive parents. Similarities and differences...
