W. Harold Grant concluded that personality types develop based on the dominant characteristics of intuition, sensing, feeling and thinking. Grant believes that up until the age of six, all areas are equal for the most part, but that during the ages of six through 12, a dominant function begins to emerge. If a person primarily relies on intuition to absorb information and prefers to do this independently, then he develops an introverted, intuitive personality type.
Operant conditioning occurs when a particular behavior is reinforced. If parents regularly encourage young children to be outgoing individuals, then that behavior trait will be reinforced and those children will most likely grow up to be extroverts who enjoy socialization. Alternatively, if parents discourage children from going out a lot and exposing them to social situations, those children will most likely develop introverted personalities.
Carl Jung believed that everyone is genetically predisposed to become either an introverted or extroverted personality type. When parents try to restrain a naturally extroverted child from socializing, that child may appear introverted later on. In adults, this may create an internal conflict unless they are able to express their true personality type.
National personality types originated in anthropology with the work of Ruth Benedict in the 1920s. Benedict thought that personality types were developed through socialization, particularly in childhood, including the development of beliefs, values and expectations. According to Benedict, culture played a greater part than genetics in determining personality characteristics, therefore, women are typically nurturing toward children and men are more aggressive due to cultural influences and how they were raised.