Psychologists using a new genetic technique have found a gene associated with high intelligence. The technique, they say, should help to identify several more of the many genes thought to affect human intelligence and personality. If the work is confirmed by other researchers, it would be the first time that a gene contributing to intelligence had been found.
The new finding is a tender green shoot arising from the ashes of a long-smoldering debate about whether intelligence is determined by people's genes or by the circumstances of their upbringing. Many psychologists now believe there is clear evidence that heredity is important but not all powerful, and that genes account for about 50 percent or more of the variance in I.Q., or intelligence quotient. Variance is a statistical measure of how widely a quality varies in a population.
The gene was pinpointed by studying about 50 students whose SAT scores were equivalent to an I.Q. score of 160 or higher, and by comparing their DNA with children of average I.Q.
The research, published in the current issue of the journal Psychological Science, was conducted by Dr. Robert Plomin, a leading American behavioral geneticist who works at the Institute of Psychiatry in London. His co-authors include Dr. David Lubinski and Dr. Camilla Benbow. Their talent search program, known as the Study of Mathematically Precocious Youth, supplied the test subjects.
Dr. Plomin has sought to move the debate forward by arguing that if genes for intelligence exist it should be possible to track some of them down through the powerful new genetic scanning techniques that have recently become available. Searching through a small part of the human genome, the long arm of chromosome 6, he found that a particular variant of a certain gene was twice as common in his sample of children with ultra-high I.Q.'s than in those with average I.Q.'s The gene has a very small effect, accounting for about 2 percent of the variance, or 4 I.Q. points, Dr. Plomin said.
So slight an effect would be expected in a trait influenced by many genes. There might be 50 or more genes affecting intelligence, experts say, and a person with a high I.Q. would have the favorable versions of only some of these genes. Only half the children with high I.Q.'s in Dr. Plomin's study had the intelligence-promoting form of the gene he detected.
Dr. Nathan Brody, a psychologist at Wesleyan University, said Dr. Plomin's finding was a small step in itself but of ''enormous significance'' if it proved to be the beginning of the detection of other genes that influence intelligence.
''I think his work is an important technical achievement,'' said Dr. John Kihlstrom, a psychologist at the University of California at Berkeley. ''He has married the human genome technology with the study of behavioral genetics.'' Dr. Kihlstrom is the editor of the journal in which Dr. Plomin's study appeared. Dr. Kihlstrom said that Dr. Plomin is a leading figure in the field of behavior genetics and that the new report was ''the first time that a gene has been associated with some specific aspect of cognition and behavior,'' with the exception of the gene governing the behavioral disorder known as Williams syndrome.
Another psychologist who studies the genetics of behavior, Dr. Thomas Bouchard of the University of Minnesota, said the new finding was ''nice ordinary science without extravagant claims'' but would require independent studies before being confirmed.
The genes Dr. Plomin has been seeking are those that affect intelligence in the broadest sense, known to psychologists as general cognitive ability. This is the quality that I.Q. tests seek to measure. Brain experts now believe that general cognitive ability is composed of many overlapping capabilities, like verbal and math skills.
The genetic variation Dr. Plomin found lies in an obscure but extremely powerful gene known as the I.G.F.2 receptor gene. The I.G.F.2, or insulin-like growth factor 2, is a multifaceted hormone about which little is known. Dr. Randy Jirtle, a molecular biologist at Duke University who studies the gene because of its involvement in cancer, said it might influence both the development and everyday metabolism of the brain, although neither role has been proved. At the least, Dr. Jirtle said, Dr. Plomin has hit on a ''plausible candidate'' for a gene that affects intelligence.
Dr. Mony De Leon, a neuroscientist at the New York University School of Medicine, said, ''This is the first step of its kind, but a very small step, toward establishing what the inherited aspects of intelligence may be.''
The variation found by Dr. Plomin and his team lies in a part of the gene's DNA that is trimmed away before the genetic message is translated into a working protein. Thus the variation probably cannot in itself affect intelligence but presumably lies next to some translated region that does.
The finding is a statistical association, not proof of causation, and requires several further steps to make the claim of an intelligence gene indisputable. Besides independent corroboration, biologists would wish to locate the translated part of the variant gene and understand how it affects intelligence.
Genetic variations like those Dr. Plomin is studying may be more common in some ethnic groups and less common in others. To prevent any ethnic effect from confounding the link between genes and intelligence, Dr. Plomin decided to confine his study to a single ethnic group, in this case white Americans.
The finding has no immediate practical importance, since the gene accounts for such a small percentage of intelligence. But Dr. Plomin says he expects to find many more such genes, including at least one on each of the 23 pairs of human chromosomes. Knowledge of these genes, and what they do, could in time help researchers understand the nature of intelligence, as well as learning disabilities and the intellectual decay that occurs in Alzheimer's disease.
But Dr. Kihlstrom said he feared a more immediate reaction. Despite the tiny effect of the gene, he said, ''I confidently predict that within two months there will be genetic centers set up for profit to test parents for this gene.'' He said such centers would be a ''crummy idea.''
Dr. Plomin and his colleagues said they were well aware of the potentials for abuse of their finding, like discriminative genetic screening and assertions that genes determine everything. ''Despite the new problems created by new findings,'' they wrote in their report, ''it would be a mistake, and futile as well, to try to cut off the flow of knowledge and its benefits in order to avoid having to confront new problems.''
