In ‘enormous success,’ scientists tie 52 genes to human intelligence
In a significant advance in the study of mental ability, a team of European and American scientists announced Monday that they had identified 52 genes linked to early 80,000 people.
These genes do not determine intelligence, however. Their combinedinfluence is minuscule, the researchers said, suggesting that thousands more are likely to be involved and still a wait discovery. Just as important, intelligence is profound ly shaped by the environment.
Still, the findings could make it possible to begin new the biological basis of reasoning and problem-solving, experts said. They could even help researchers determine which interventions would be most children struggling to learn.
“This represent san enormous success ,” said Paige Hard en, 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 overall, 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. N eur os ci en tis ts 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 thatsomething to do with how efficiently a brain can send signals from one region to another.
Danielle Post hum a, a geneticist at Vrije University Amsterdam and senior author of the new paper, first became interested in the study of intelligence in the 1990 s. “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?”
Post hum a 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.
In 2014, Post hum a was part of a large-scale study of more than 150,000 people that revealed 108 genes linked to schizophrenia. But she and her colleagues had less luck with intelligence, which has proved a hard nut to crack for a few reasons.
Standard intelligence tests can take along time to complete, making it hard to gather results on huge numbers of people. Scientists can try combining smaller studies, but they often have to merge different tests together, potentially mas king the effects of genes.
As a result, the first generation of genome-wide associationintelligence failed to find any genes. Later studies managed to turn up promising results, but when researchers turned to other groups of people, the effect of the genes again disappeared.
But in the past couple years, larger studies relying on new statistical methodsfinally have produced compelling evidence that particular genes really are involved in shaping human intelligence.
“There’ s a huge amount of real innovation going on ,” said Stuart J. Ritchie, a geneticist at the Universityof Edinburgh who was not involved in the new study.
Post hum a and other experts decidedto merge data from 13 earlier studies, forming a vast database of genetic markers and intelligence test scores. After so many years of frustration, Post hum a was pessimistic it would work.
“I thought ,‘ Of course we’ re not going to find anything ,’” she said.
She was wrong. To her surprise, 52 genes emerged with firm links to intelligence. A dozen had turned up in earlier studies, but 40 were entirely new.
But all of these genes together account for just a small percentage of the variation in intelligence test scores, the researchers found; each variant raises or lowers IQ by only a small fraction of a point.
“It means there’ s along way to go, and there are going to be a lot of other genes that are going to be important ,” Post hum a said.
Christopher F. Ch a br is, a co-author of the new study at Ge is in ger Health System in Danville, Pennsylvania, was optimistic that many of those missing genes would come to light, thanks to even larger studies involving hundreds of thousands, perhaps millions, of people.
“It’ s just like astronomy getting better with bigger telescopes ,” he said.
In the new study, Post hum a and her colleagues limited their research to people of European descent because that raised the odds of finding common genetic variants linked to intelligence.
But other gene studies have shown that variants in one populationcan fail to predict what people are like in other populations. Different variants turnout to be important in different groups, and this may well be the case with intelligence.
“If you try to predict height using the genes we’ ve identified in European sin Africans, you’ d predict all Africans are 5 inches shorter than Europeans, which isn’ t true ,” Post hum a said.
Studies like the one published today don’ t mean that intelligence is fixed by our genes, experts noted.“If we understand the biology of something, that doesn’ t mean we’ re putting it down to determinism ,” Ritchie said.
As an analogy, he noted that nearsightedness is strongly influenced by genes. But we can change the environment—in the form of eye glasses—to improve people’ s eyesight.
Hard en predicted that an emerging understanding of the genetics of intelligence would make it possible to find better ways to help children develop intellectual ly. Knowing people’ s genetic variations would help scientists measure how effective different strategiesare.