Around the same time, Ronald Kessler and his colleagues published a study in the prestigious Archives of General Psychiatry in which they concluded that "about half of Americans will meet the criteria for a DSM-IV disorder [Fourth Edition of the American Psychiatric Association s Diagnostic and Statistical Manual of Mental Disorders] sometime in their life, with first onset usually in childhood or early adolescence." Critics, of course, could explain this finding on the basis of the DSM s tendency to label a wide range of subjective states and deviant behavior as "mental disorders." The authors of the DSM-IV seem to be saying to us (with apologies to comedian George Carlin), "You are all diseased."

But suppose that Kessler, et al., despite whatever flaws their study may have contained, did show that a sizable portion of Americans will experience some level of chronic or acute psychological dysfunction or distress during their lifetimes. Having established this, the question remains open whether the causes are mainly biological, or whether they reflect the impact of a wide range of psychologically harmful environmental influences that people experience in American society.

An important pillar of the biological argument is genetic theory, which holds that most people diagnosed with psychiatric disorders are genetically predisposed to manifest these disorders. However, if 50% of Americans will develop a genetically-based mental disorder, according to genetic theory a sizable percentage of the 50% who do not develop a mental disorder nevertheless carry pathological genes. Thus, according to the logic of the American Psychiatric Association s Diagnostic and Statistical Manual of Mental Disorders, and currently ascendant theories of genetic causation, a sizable majority of Americans carry pathological genes predisposing them to mental disorders.

Or, perhaps not. In this book, I assess the surprisingly shaky foundations of genetic theories in psychiatry in the context of the current crisis in psychiatric molecular genetic research. It was expected that genes for the major psychiatric disorders would have been found by now. However, they have not been found. Indeed, a prominent genetic researcher could write in the July, 2005 edition of the American Journal of Psychiatry as follows: "The strong, clear, and direct causal relationship implied by the concept of a gene for does not exist for psychiatric disorders. Although we may wish it to be true, we do not have and are not likely to ever discover genes for psychiatric illness." It remains to be seen whether statements such as this will lead to the abandonment of gene searches for psychiatric disorders in the near future.

A belief in the hereditary basis of mental disorders is a very old one. In this book I will show that, following a critical reading of the scientific literature, this age-old belief has little evidence in its favor.