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.
And yet genetics cannot be the whole story: identical twins, who have virtually the same DNA, do not always develop the same mental disorders. For example, if one identical twin acquires schizophrenia, the other stands just a 50 percent chance of also suffering from the disease. Indeed, abundant data suggest that psychiatric ailments typically result from a complex interplay between the environment and a number of different genes [see “The Character Code,” by Turhan Canli; Scientific American Mind, February/March 2008]. But only recently have scientists begun to grasp how the environment affects the brain to produce psychological changes.