The show began as a sitcom about four geeky, male scientists and their fun-loving, under-educated, socially successful waitress neighbour. Much of the humor revolved around the differences between scientists and the rest of the characters, especially Penny. From season 3 onwards, the show changed greatly into being a show about couples and families. Bernadette Rostenkowski was brought in during season 3 and started a relationship with Howard. The couple later married and had a daughter. Amy Farrah-Fowler was also brought in during season 3 and started a relationship with Sheldon; they later got engaged. Leonard and Penny became a couple and married. The show frequently shuffles between romantic comedy and relationship drama.