Chapter fourteen touches on the different types of personality's people have and how they are come to have them. There were case studies done on about 130 identical and fraternal twins showing signs of specific gene related personality traits that a set of twins shared even though separated from birth, such as similar views on divorce, religion and also the inclination to watch TV. There were other differences found due to environmental influences, but the genetic similarities were more prominent.
Other parts of the chapter talk about the different developmental stages people go though starting at birth, which is called the Oral Stage (Freud's Stages of Psychosexual Development). These stages "end" around age twelve at the, Genital Stage, when the genetics and environmental factors begin to show who a person has become. It is explained later in the chapter that different personality traits such as extraversion, neuroticism or "openness" seem to define a person (but can also be strengthened or toned down, depending on the personality) until around the age of thirty. The chapter battles back and forth regarding the different views and theories of the Freudians and Skinnerians on unconsciously processing things and the behaviors one has which then creates a personality.