Are schizophrenia and manic-depressive disorder biological or the result of a traumatic upbringing? Are some people genetically destined to become schizophrenic? This book, the result of a landmark study, provides compelling evidence that both schizophrenia and manic-depressive disorder are biologically based diseases of the brain, unrelated to psychological influences. E. Fuller Torrey and his colleagues conducted the largest study ever of pairs of identical twins in which one suffered from schizophrenia or manic-depressive disorder and the other did not, and discovered that the former almost always have structural and functional changes in their brains. The researchers concluded that while these diseases have a genetic component, they are most likely triggered by an outside biological force, such as a virus, either in utero or in infancy. The book establishes for the first time that the disease may originate very early in life, even though symptoms don't appear until young adulthood. Moreover, the authors show that - contrary to prevailing wisdom - schizophrenia does not change a person's underlying personality. Weaving poignant psychological portraits of twins through the book, the authors show how these case studies support the research findings. Here is an important contribution to the ongoing debate over the origins of mental illness.