Nurture or nature? Biology or environment? Why are some people intelligent, or personable, or creative and others obtuse, or shy, or unimaginative? Although each human being is a unique mixture of positive and negative traits and behaviors, the question remains: What is the neurobiological basis for each individual’s makeup? For example, why does one person suffer from a disorder (e.g., ADHD, autism, mental retardation) and another lives free of maladies?