The Lure of Determinism

Sharon Begley has another wonderful column today in the WSJ. She focuses on the so called "violence gene" as an example of the hopelessly complicated relationship between genetics and real life.

In the late 1980s, a number of men in several generations of a large Dutch family were found to carry a mutation in the MAOA gene that made it inactive. They all had a long rap sheet of rape, attempted murder and arson. MAOA became known as the "violence gene," headlines warned of "a violence in the blood," and there was talk of screening everyone to identify carriers.

The link between MAOA and aggression made biological sense. MAOA breaks down brain chemicals, including serotonin. It comes in two forms, short and long. The short form, which about one-third of people have, can't do the breaking down as efficiently as the long form, disrupting the balance of neurotransmitters in the brain. The result was thought to be higher levels of aggression, as measured by a surge in activity in the brain's fear region -- the amygdala -- at the sight of an angry face. That might explain the hair-trigger tempers in that Dutch family.

In a study of 531 U.S. men, however, the violence gene didn't live up to its billing. When psychologist Stephen Manuck of the University of Pittsburgh analyzed men carrying the short form of the MAOA gene, he told the ICN meeting, only those who held antisocial attitudes, who received little parental affection as kids and whose fathers had low levels of education also had a history of aggression. Presumably, dad's low education is a marker for other traits, perhaps how he treats his kids.

"Men with none of these risk factors for aggression had the same low level of lifetime aggression even if they had the short form of the MAOA gene," says Prof. Manuck. That suggests the gene isn't associated with aggression per se, he says, but instead is tied to putting the brakes on tendencies that already are present for other, often environmental, reasons.

Another gene follows the same pattern. It makes a serotonin receptor in the brain and also comes in two forms. One form, which creates a slightly different version of the serotonin receptor, is associated with antisocial behavior and aggression, but only in men whose fathers never finished high school, Prof. Manuck finds. Again, dad's education is undoubtedly a proxy for something that acts directly on his children.

It should have been clear that the short form of the serotonin-receptor gene is no Jack-the-Ripper DNA. Some two-thirds of Japanese carry the short form, but that population isn't known for violence. That suggests something in Japanese culture or child-rearing practices defuses the gene's supposed effects.

So even though genetic determinism continues to enthrall the public, biology is now documenting the strange dialectic between DNA and experience, genotype and phenotype. Begley ends with a wonderful quote:

"Even for scientists, it's much easier to say this gene is related to this behavior," says Prof. Francis. "People have a hard time understanding that experience and social factors are transduced into biology. ... It's a radical idea."