A team of European and American scientists announced that they had identified 52 genes linked to intelligence in nearly 80,000 people. These genes do not determine intelligence, however. Their combined influence is minuscule, the researchers said, suggesting that thousands more are likely to be involved and still await discovery. Just as important, intelligence is profoundly shaped by the environment. Still, the findings could make it possible to begin new experiments into the biological basis of reasoning and problem-solving, experts said. They could even help researchers determine which interventions would be most effective for children struggling to learn.
“This represents an enormous success,” said Paige Harden, a psychologist at the University of Texas, who was not involved in the study.
For over a century, psychologists have studied intelligence by asking people questions. Their exams have evolved into batteries of tests, each probing a different mental ability, such as verbal reasoning or memorization.
In a typical test, the tasks might include imagining an object rotating, picking out a shape to complete a figure, and then pressing a button as fast as possible whenever a particular type of word appears.
Each test-taker may get varying scores for different abilities. But over all, these scores tend to hang together — people who score low on one measure tend to score low on the others, and vice versa. Psychologists sometimes refer to this similarity as general intelligence.
It’s still not clear what in the brain accounts for intelligence. Neuroscientists have compared the brains of people with high and low test scores for clues, and they’ve found a few.
Brain size explains a small part of the variation, for example, although there are plenty of people with small brains who score higher than others with bigger brains.
Other studies hint that intelligence has something to do with how efficiently a brain can send signals from one region to another.
Danielle Posthuma, a geneticist at Vrije University Amsterdam and senior author of the new paper, first became interested in the study of intelligence in the 1990s. “I’ve always been intrigued by how it works,” she said. “Is it a matter of connections in the brain, or neurotransmitters that aren’t sufficient?”
Dr. Posthuma wanted to find the genes that influence intelligence. She started by studying identical twins who share the same DNA. Identical twins tended to have more similar intelligence test scores than fraternal twins, she and her colleagues found.
Hundreds of other studies have come to the same conclusion, showing a clear genetic influence on intelligence. But that doesn’t mean that intelligence is determined by genes alone.
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