“Smart” genes associated with human intelligence have been identified for the first time. But scientists say they have only scratched the surface, with potentially thousands of genes relating to IQ still to be discovered.
While twin and family studies have long indicated differences in cognitive performance is genetic, the exact genes associated with IQ have remained a mystery.
Results of a large international study of 126,000 people from Australia, Europe and America has identified three genetic variations associated with intelligence.
The team, including Australian researchers, also identified four specific genes that influence cognitive performance. Each gene is associated with a particular pathway in the brain relating to the main cellular mechanism for learning and memory.
Humans have about 20,000 genes in their genome. The four genes identified are likely to be among numerous “smart” genes with scientists confident there are thousands of genes relating to IQ.
Queensland Brain Institute geneticist Beben Benyamin said that, individually, each gene identified would have a minuscule impact on overall intelligence scores. But collectively, all genes that influence intelligence make a difference.
The three genetic variations identified in the study as having an impact on intelligence added up to barely two points on the IQ scale.
On that scale, 100 points is the mean IQ score. If a person had each of the three genetic variations identified, it would give them an advantage of only 1.8 points.
“It probably doesn’t mean anything in terms of day-to-day differences,” Dr Benyamin said. “It tells us that there is no such thing as one big gene affecting intelligence.”
The applications of the study findings have broader implications, including for the study of neurodegenerative conditions such as dementia and Alzheimer’s disease, which reduce cognitive performance.
More broadly, intelligence has a bearing on lifestyle.
“A lot of things are positively correlated with IQ, things like income, job performance and health,” Dr Benyamin said.
Participants in the study had their DNA analysed and compared with their educational outcomes.
The findings were published in the science journal PNAS on Tuesday.