Does being the oldest or youngest sibling really shape your personality?

Are you a responsible oldest child, an overlooked middle, or a free-wheeling baby? For those who adhere to the theory that birth order influences personality, the answer to that question may hold the key to who you are as a person. At parties, family dinners, and therapy sessions, people can use birth order as a kind of shorthand for personality traits—an only child’s selfishness, perhaps, or a middle child’s struggle for visibility.