A major study into the genetics of human intelligence has given scientists their richest insight yet into the biology that underpins our cognitive skills.

The research on 60,000 adults and 20,000 children uncovered 40 new genes that play a role in intelligence, a haul that brings the number of genes known to have a bearing on IQ to 52.

Forming part of the blueprint for the brain, the genes provide instructions for the building of healthy neurons, the paths they take through the 3lb lump of tissue, and the construction of hundreds of trillions of synapses that connect them.

“We want to understand how the brain works and learn what are the biological underpinnings of intelligence,” said Professor Danielle Posthuma, a statistical geneticist at the Free University of Amsterdam, who led the study published in Nature Genetics.



Previous work with twins has shown that genes account for about half of the difference that is seen in IQ scores across the population, with the rest being shaped by factors such as conditions in the womb, nutrition, pollution and a person’s social environment. “Genes do not determine everything for intelligence,” said Posthuma. “There are so many other factors that affect how well someone does on an IQ test.”



It is thought that hundreds, if not thousands, of genes play a role in human intelligence, with most contributing only a minuscule amount to a person’s cognitive prowess. The vast majority have yet to be found, and those that have do not have a huge impact. Taken together, all of the genes identified in the latest study explain only about 5% of the variation in people’s IQs, the scientists found.



Working with an international team of scientists, Posthuma looked for genetic markers linked to intelligence in 13 different groups of people of European descent. Amid the 52 genes they found, 40 were new ones that predominantly switched on in the brain. The same genes were also associated with better educational attainment, a larger head circumference at birth, living longer, and autism.



While scientists have an idea what many of the newfound genes do, Posthuma said the next step was to block their function in mice to see what impact each gene has on brain function. The same could be done with human neurons made from skin cells in the lab, she said. In time, if researchers can build up a detailed picture of the genetics of intelligence, it could help them understand what goes wrong in conditions that lead to mental impairment.



But research on the genetics of IQ has always raised serious questions about how the information might be used. Could human embryos be chosen according to their future brain power? Could scientists make drugs to enhance human intelligence? If so, would only the richest have access to such powerful technology? “There is always the question of designer babies and can we use this knowledge to improve intelligence,” said Posthuma. “These are valid questions, but it’s very far from where we are now. You certainly wouldn’t be able to design a baby based on the current knowledge.”



Such uses are on the horizon. IVF embryos are already screened for genetic faults. With larger studies, scientists expect to find more genes that contribute to intelligence. Eventually, the work may reach a point where the genomes of IVF embryos could be used to rank them according to their intellectual potential, even if the difference is so small as to be insignificant. “You can imagine that as soon as it becomes possible to explain a good deal of the variance in intelligence, people are going to start doing this,” said Stuart Ritchie, a researcher in cognitive ageing at Edinburgh University and author of the book Intelligence: All that Matters.



The prospect of IQ-boosting drugs should not be dismissed either, Ritchie added. The world is home to an ageing population and cognitive function declines in old age, leaving the aged more prone to error and accidents, more vulnerable to scammers. “If we know what genes are involved, and we can develop the treatments, then we might be able to stave of that cognitive ageing to some degree,” he said. “Over time, you could see an inequality growing there.”



Another long-term prospect, perhaps, is using genetic information to tailor teaching for individual students, Posthuma said. “Maybe one day we can say that based on your genetic makeup, it could be easier for you to use this strategy rather than that one to learn this task. But that’s still very far off,” she said. “I don’t think what’s written in our genes determines our lives.”