Free What You Can Change . . . And What You Can't*: The Complete Guide to Successful Self-Improvement by Martin E. Seligman

records of the sons have been scrutinized.
    If neither the natural nor the adopted father had ever been convicted of a crime, 10.5 percent of the sons turned out to be criminals. If the adopted father was a criminal, but the natural father was not, 11.5 percent of the sons were criminals, an insignificant difference. So having a criminal rearing a child does not increase the child’s risk of himself becoming a criminal.
    If the natural father (whom the child had not seen since he was, at most, six months old) was a criminal, but the adopted father was not, 22 percent of the sons were criminals. Crime rate is doubled by having “criminal genes.” If both natural and adopted fathers were criminals, the sons’ crime rate was 36.2 percent—more than triple the rate of the sons of upstanding fathers.
    This means that there is a biological predisposition to commit crime (and to get caught). If it is present and you are reared by a criminal father, you are at very high risk. Merely having a criminal father rear you, without the biological predisposition, does not increase your risk. 22
    So crime, astonishingly, is heritable. Similar adoptive studies strongly confirm the findings of the twin studies: Most of human personality has a strong genetic component.
    The other major finding of the adoption studies is that two children raised in the same family are almost as different from each other as any two random kids—on almost every measure of personality and intelligence—once you take genes into account. There is no similarity between two children adopted into the same family; everyone who has raised two adopted kids knows this, but others who have only ideology to guide them greatly overestimate the importance of the family environment. This revolutionary finding—which suggests that many of our labors in childrearing are simply irrelevant—will be discussed later.
    But for every one of these heritable traits, the degree of heritability is much less than 1.00. Generally, it hovers a bit below .50. This means that our personality is not utterly determined by our genes—far from it—but it also means that much of what we are is contributed to by our genes.
    Conclusion and evaluation . So the final principle of biological psychiatry is firmly in place: A massive body of research in the last ten years has shown that personality is heritable. Add this to the principles that mental illness is physical illness and that drugs change our emotions and mood, and you arrive at a powerful view of human nature.
    Biological psychiatry, as a philosophy of mental illness, must be taken seriously. But I have three caveats—one for each principle.
    First: That mental illness is physical illness has been demonstrated for only one mental illness—general paresis. The claims for schizophrenia, Alzheimer’s, and manic-depression are plausible but unproven—no biochemical causes have yet been located. The claims for depression, anxiety, sexual problems, overweight, and post-traumatic stress disorder are merely part of an ideological agenda, with very modest evidence to back them up.
    Second: The claim that mood and emotion are just brain chemistry and that to change you merely need the right drug must be viewed with skepticism. The basic drug discoveries to date warrant only modest enthusiasm. There are indeed drugs that alter mood for some—but not all—people. All of these drugs are cosmetic, however, and all of them produce unwanted side effects, some of which are awful.
    Third: The claim that personality is inherited has strong evidence behind it. But, at most, personality is only partly genetic. The degree of heritability hovers below .50 for all personality traits (except for IQ, which may be around .75). Even by the most extreme estimates, at least half of personality is not inherited. This means that, at most, half of personality is fixed. 23 The other half of personality comes from what you do and from what happens to you—and this