Biological Risk Factors for Challenging Behavior
Scientists are leaning more and more toward the view that a gene specifically "for" a disorder or condition such as antisocial behavior is very unlikely (Rutter, Moffitt, and Caspi, 2006). Dean Hamer, director of the Gene Structure and Regulation Unit at the National Cancer Institute, writes, "Human behaviors, and the brain circuits that produce them, are undoubtedly the product of intricate networks involving hundreds to thousands of genes working in concert with multiple developmental and environmental events" (2002, p. 72).
Because there are so many elements involved and they interact with one another in such complex ways, it is extremely difficult to disentangle the influence of genes from the influence of the environment. To tease out these different strands and estimate their relative power, behavioral geneticists use twin studies, comparing identical twins (who share all their genes) and fraternal twins (who share about half their genes). The genetic influence on a characteristic such as intelligence, temperament, personality, cognitive style, or psychophysiology is greater when the trait is more similar in identical twins than in fraternal twins. Researchers also study adopted children to see if they are more like their biological parents (with whom they share genes) or their adoptive parents (with whom they share the environment). These studies, which are becoming increasingly analytical and sophisticated, show that antisocial behavior is moderately heritable (Moffitt, 2005), especially antisocial behavior that begins early in life (Arseneault et al., 2003; Rhee and Waldman, 2002).
In addition, scientists have discovered that some genes interact with a particular environment to actually produce a disorder (Rutter et al., 2006); some genes are expressed or turned on (or not) because of physical, social, and cultural factors in the environment; and some genes—for example, those that influence difficult temperament, impulsivity, novelty seeking, and lack of empathy—predispose people to be exposed to environmental risks. Genes even help shape the environment. Genes influence how parents bring up their children; genes affect the responses that children evoke from their families and the others around them; and, as children grow older, genes sway their choice of companions and surroundings (Caspi and Silva, 1995; Plomin, Owen, and McGuffin, 1994).
It's important to remember that heredity is not destiny. With the right environmental interventions at the right time, even a trait with a strong genetic foundation (such as antisocial behavior) can be altered.
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