By studying cooperation -- and struggles -- psychologist Hill Goldsmith studies how genes affect young personalities. ©1997, University of Wisconsin-Madison Office of News and Public Affairs. Photos by Jeff Miller.
If genetics plays a major role in the cognition of older Swedes, what does it do to youngsters in the Why Files'
backyard? Psychologist Hill Goldsmith studies the genetic influence on the personality of twins. Goldsmith doesn't take the typical approach of asking parents to fill out questionnaires. Instead, he puts the little monsters in his laboratory at the University of Wisconsin-Madison and straps electrodes to their brains.
Just kidding. But he does watch them play in the lab, and also presents them with structured activities that allow for easy comparison between kids. These activities are not all burdensome. For example, one that's sure to appeal to any kid -- whether twin, singleton or 45 years old -- is a search-and-destroy soap bubble hunt. "Children like to pop them," Goldsmith says. "They do this naturally. But some do it in an easy-going way, wait for them to come down before popping them. Others play very vigorously, jumping in the air and trying to pop the biggest bubble."
By itself, he says, this single finding may mean nothing. "But if we see the same thing across many activities in many different contexts, you begin to suspect that if development continues along the same pathway, this will develop into an active, energetic personality."
Did you catch that? Goldsmith is not arguing that personality always develops smoothly or predictably. And yet, as many parents know, 
kids' personalities can surface quite early.
And while the Swedish twin study showed a fairly high level of inheritance on intellectual abilities, Goldsmith says he's finding a "moderate level of genetic effects, not extremely strong, on personality. We're not painting a very deterministic picture." And even though the kids are being raised in very similar environments, "Our studies have found environmental variations are very important for differences in personality."
Why wouldn't identical twins who were raised in the same household end up as identical adults? Because, Goldsmith says, "There may be aspects of the environment that the child helps to construct themselves." For example, they might choose different friends or activities, or suffer different accidents.
More cautions on the road to wisdom
Furthermore, when you read about twin studies, you should understand that they do not show that genes cause individuals to behave a certain way. Instead, Goldsmith and other twin researchers actually study how much genes explain the similarity or difference in a group. "When you hear that the heritability of shyness is 60 percent," he stresses, "that means that if you take 100 [or any other large number of] individuals with different levels of shyness, 60 percent of that variation is accounted for by genetic differences."
But that's a difficult distinction to express or understand, and it's probably more boring than crediting our smarts to Great Aunt Jean, who won the national spelling bee with new-fangled words like "penicillin" and "nuclear." Yet twin studies can't prove that, Goldsmith insists. "People think my particular intelligence level is, say, 60 percent due to genes, but that's not accurate. It's the variation, not the absolute amount, that's explained by genetics." Twin studies, he explains, are "unable to untangle the way genes and environment are likely to interact in the life of an individual."
In an entirely separate realm of entanglement, The Why Files is happy to learn that romantic love styles depend little on genetics. That's the word from Niels Waller, a psychologist at the University of California at Davis, who concluded with his colleagues that "individual differences in romantic love style are almost entirely due to environment." In other words, the family we grew up in has more to do with our gooey-eyed behavior than the DNA twisted inside our cells (see "The Importance of Nongenetic..." in the bibliography)
You haven't mentioned how parents cope with a mass of multiples.
