Intelligence genes prove hard to map

Sharon Schmickle
Star Tribune
 

BOSTON -- Couples who have dreamed that genetic research might enable them to produce little Einsteins should put that expectation on hold indefinitely, experts said Sunday at a meeting of the American Association for the Advancement of Science.

Despite widespread predictions that parents would use new genetic tools to select for smarter children, scientists haven't been able to identify genes that would tell whether a child is going to be highly intelligent, said Matthew McGue, a University of Minnesota psychology professor who specializes in IQ studies.

Some genes that play a role in mental retardation have been isolated, he said. But McGue and other experts in behavioral genetics said researchers are finding the genes that influence overall intelligence and behavior to be more elusive and complex than had been expected a few years ago.
 

Dozens of genes work together to influence intelligence, it now appears, much like an orchestra playing a difficult score. Scientists are giving up on earlier hopes for finding one or two prominent soloists, said Jonathan Beckwith, a professor of microbiology and medical genetics at Harvard Medical School.

In terms of identifying all of the significant players, "putting together the full orchestra is way, way off". he said.

Even if that were done, he said, "being able to safely fiddle around with that many genes is unimaginable"

Behavior geneticists should take some of the blame, Beckwith said, for having created simplistic expectations that it would be easy to find a few genes that could explain intelligence and behavior.

The contagious enthusiasm for gene hunting that dominates so much scientific research today obscured some important points in the longstanding nature-nurture arguments about intelligence and behavior, several experts said.

Beyond science circles, the media and policymakers have been too quick to generalize results from preliminary research findings, they said.

About 150 genes and regions on chromosomes have been identified in studies as possibly influencing cognitive ability, McGue said.

"None of these are unequivocal at this point"; he said.

The failure to pinpoint genes doesn't diminish their importance for understanding intelligence, McGue said.

The classic yardstick for genetic effects -- comparative studies of twins reared apart and together -- suggests that genetic factors explain about half of the variation on IQ tests.

But parents need not feel like passive players in the shaping of a child's intelligence because a home environment could even out some of the differences in natural intelligence. Studies of children placed in stimulating and encouraging adoptive homes show that such an environment can help improve IQ, McGue said. And the opposite environment could suppress some natural potential.

Factors outside the home make a difference too. IQs have risen phenomenally over the past half-century, McGue said.

"What we all suspected when we were growing up and arguing with our parents is that we are getting smarter", he said.

It turns out that that is true, at least on a large scale. "The population is getting smarter at a remarkable rate if we are to believe IQ tests"; he said.

Average IQs have risen between 3 and 5 points a decade in several countries, he said.

The reason could be the same reason that people have grown taller during the same time span: improvements in nutrition and health care.

McGue credited an improved education system, too. It wasn't until the 1950s that most adults were able to graduate from high school and share their intellectual gains with their children, he said, and that apparently makes a difference.

McGue also speculated that IQ is influenced by the fact that people increasingly use their brains for work and play in a technologically and intellectually demanding environment.

"Day in and day out being exposed to that intellectual challenge, I think, does actually result in increases in IQ", he said.

Of course, the collective gain could be small comfort for ambitious parents who want their children to stand out intellectually. It leaves them, essentially, in the proverbial Lake Wobegon, where all of the children are above average.

The take-home lesson, McGue said, is that IQ can change.

Meanwhile, researchers haven't given up the search for the genes that are involved. One of the greatest challenges, McGue said, is not merely to identify genes but to learn to see them in the light of their interplay with the environment.

-- Sharon Schmickle is at

 sschmickle@startribune.com .