Throughout history shamans, clerics and physicians have tried to pin down what goes awry when a person slips into sadness, insanity or psychosis. Theorists have variously blamed mental illness on an imbalance of bodily fluids, the movement of planets, unconscious mental conflict and unfortunate life experiences. Today many researchers believe that psychiatric disorders arise in large part from a person’s genetic makeup. Genes, after all, are the blueprints for the proteins that create and control the brain.