SCIENTISTS, LIKE MOST MORTALS, grow attached to which ever theory works. For geneticists, it's a model that one researcher calls OGOD. It stands for "one gene, one disorder," and it means that a single gene causes, and is enough by itself to cause, a disease. Huntington's and cystic fibrosis are two single-gene diseases for which researchers have identified the culprit DNA; there are scores of others. But lately, the eries of"OGOD" from biology labs have not been whoops of victory in nabbing yet another disease gene. They have instead been cries of dismay as some researchers apply the OGOD model to traits and behaviors as complex as "novelty seeking" and schizophrenia. "Looking for single genes for complex behaviors reminds me of the old story of losing your wallet in a dark alley but looking for it under the street lamp because the light is better there," says Robert Plomin, a behavioral geneticist at the Institute of Psychiatry in London. Critics outside the field are even harsher. "Many of these 'results' [in behavioral genetics] disappear when you do the statistics right," psychologist Helena Kraemer of Stanford University told a recent meeting at the Institute of Medicine in Washington. "Fallacious methods are very common."
The latest offering in "the gene for..." sweepstakes is "happy DNA." In the current issue of the journal Nature Genetics, molecular biologist Dean Hamer of the National Cancer Institute reviews studies suggesting that one's baseline level of happiness-the very small range within which one's happiness level fluctuates--is "largely a matter of heredity." Identical twins (who have exactly the same genes) are alike in their happiness level 44 percent of the time, according to studies at the University of Minnesota. Fraternal twins, who are no more genetically similar than other siblings, are alike only 8 percent of the time. "These data show that the broad heritability of well being is 40 to 50%," Hamer writes. Moreover, people's happiness levels seem extraordinarily stable through the years (NEWSWEEK, July 29); they are affected neither by winning a lottery nor by becoming paralyzed. Studies of twins suggest that 80 percent of this stable component of happiness is heritable. "How you feel right now is about equally genetic and circumstantial," says Hamer. "But how you'll feel on average over the next ten years is fully 80% because of your genes." Though no one has identified genes wearing teeny smiles, Hamer suggests that a good place to look would be the DNA involved in the brain's "pleasure chemical," dopamine. This molecule is released in the brain after good food or good sex, for instance. "I don't think there will be a gene for happiness," Hamer says, "but rather many genes, each explaining maybe 1 percent" of someone's happiness level.
Critics argue that nongenetic reasons can explain why identical twins' happiness levels are more closely correlated than those of fraternal twins. Perhaps people who are treated better by society by parents, teachers, store clerks, cops--are, all things being equal, happier than those treated shabbily, suggests Stanford's Kraemer. Perhaps, too, one is treated better if one is attractive, thin or even-tempered. Or if one is not a member of a minority group. All of these traits are partly or completely under genetic control. Then is it not possible, Kraemer asks, that this thing called "happiness" is not itself genetic but is instead a proxy for traits that are? "Although a high heritability is being claimed," she says, "in fact the whole explanation may be environmental."
It would not be the first time that a genetic explanation collapsed. All sorts of complexities can trip up researchers. One of the biggest comes when scientists try, as Hamer does, to calculate "heritability," which is supposed to be a measure of how much of the variation in a trait from one person to the next is explained by genes. (What's not explained by genes is accounted for by people's different "environments," which include everything from obstetrical complications to education, relationships and wealth. …