“There are a small number of debilitating conditions with a strong genetic basis, such as muscular dystrophy or Huntington’s disease. These are rare, affecting about one person in ten thousand or even fewer. They do not pose a significant threat to the survival of the species. If, however, we add up the numbers of people plagued by depression or ADD or the other common psychological problems people in this society struggle with, including alcoholism and anxiety, we will have identified no less than a third of the North American population.

Genetic explanations for these conditions assume that after millions of years of evolution, nature would permit a very large number of disordered genes, handicapping a third of humankind, to pass through the screen of natural selection — a highly unlikely proposition.”