“In fact, some scientists are starting to explore the idea that reward-sensitivity is not only an interesting feature of extroversion; it is what makes an extrovert an extrovert. Extroverts, in other words, are characterized by their tendency to seek rewards, from top dog status to sexual highs to cold cash. They’ve been found to have greater economic, political, and hedonistic ambitions than introverts; even their sociability is a function of reward-sensitivity, according to this view—extroverts socialize because human connection is inherently gratifying.”