Personality and the ability for conscious thought have long been hallmarks of our species. We often define ourselves by the choices we make, but to what extent is personality the result of conscious thought? This National Geographic Special Issue, Your Personality Explained, looks at the impressively adaptable and incredibly sensitive human brain and explores how your brain develops your personality over time and in response to the world around us. Even identical twins may develop in drastically different ways, begging the question: How do we become who we are?