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Unraveling the nature of the beast


Nurture got a poke in the eye from nature last week, with the publication of a wide-ranging study of identical and fraternal twins that showed differences in certain attitudes are partly due to genetic factors.

James Olson and colleagues at the University of Western Ontario surveyed 336 pairs of adult Canadian twins, asking them detailed “attitude questions” ranging from their feelings toward the death penalty to their views on roller coasters. All the sets of twins had been raised together, so had been exposed to similar environmental influences when growing up. Questions followed a format of “My overall attitude to doing crossword puzzles is” and allowed answers from “extremely favorable” to “extremely unfavorable.”

To identify which sorts of attitudes were more influenced by genetic factors, the researchers compared the responses from fraternal twins (141 pairs of same-sex siblings) with those from identical twins (195 pairs).

Twenty-six out of 30 attitude categories indicated some sort of genetic influence, and five categories had a strong genetic factor. Those five? Attitudes toward abortion, reading books, playing organized sports, the death penalty for murder . . . and roller coasters.

Four attitude questions were totally unaffected by genetic factors: attitudes toward separate roles for men and women, easy access to birth control, being assertive . . . and playing bingo.

The results, published in the Journal of Personality and Social Psychology, are likely to send quite a few psychologists into denial. After all, it is a long-cherished belief in psychology that attitudes are learned, not preprogrammed. And while people don’t mind accepting that a gene might influence eye color, suggest that anything we consider human — like intelligence or our attitude to abortion — might also be attributable to our genes, and people get annoyed.

But why? This debate — nature versus nurture — has only really been a debate since the late 1970s. Back in Shakespeare’s day, before we knew what genes were, there was less of a problem in accepting that something in our nature shapes us. “A born devil, on whose nature nurture can never stick,” bemoaned Prospero of the monster Caliban. But in the ’70s and ’80s, the idea that we may be influenced by our genes, let alone that our nature may be determined by them, was fiercely resisted in some quarters.

It’s long past time to lay this old debate to rest. Both the things we grow up with and experience as well as the biological frame that those experiences are built on will affect how we develop. “I doubt the nature/nurture argument will ever disappear,” said Olson, “although the reality is that both components are necessary for all expressions of life.”

Even if, as seems likely, it becomes generally accepted that genes influence human characteristics, it is another problem altogether to explain how they do so. How on earth do genes produce feelings about the death penalty?

No one is suggesting that there is likely to be a single gene for enjoyment on roller coasters, like there is a gene for blue eyes. But the researchers found that physical attributes and certain personality traits — which are themselves known to be highly heritable — were strongly connected with certain attitudes.

Not surprisingly, athletic ability, which is strongly related to genetically inherited traits such as musculature and size, agility and reaction speed, is strongly related to attitudes toward sports.

“A person with inherited physical abilities such as good coordination and strength might be more successful at sports than less athletically inclined individuals, resulting in the more athletic person developing favorable attitudes toward sports,” write the researchers.

Moreover, physical attractiveness, the authors suggest, could lead to deferential treatment and an increased confidence in leadership. Similarly, naturally outgoing, sociable people may gravitate to positions of leadership.

“Presumably, these characteristics predisposed individuals to form particular kinds of attitudes, thereby contributing to the genetic determination of individual differences in those attitudes,” the researchers added.

Despite their findings, the authors stressed that it was the unique experiences of each member of a twin pair that had the strongest effect on attitudes, and concluded with a sensible message, pleading unity: “In the long run, we stand to gain the most understanding from perspectives that integrate biology and experience in accounting for individual differences.”