Many genes make you smart

Twin studies have long shown that general intelligence is strongly heritable, which suggests that genes play a substantial role in shaping our smarts.

However, the hunt for a one or a handful of genes that determine intelligence has proven fruitless, and for good reason: there is no ‘gene for intelligence’, but rather many variations that influence someone’s intelligence.

A new study published today in Molecular Psychiatry by researchers in Scotland and Australia surveyed 549,692 individual single nucleotide polymorphisms (SNPs) of 3,511 unrelated adults and found that variations in SNPs account for around half of the variation in intelligence.

They looked at two types of intelligence: crystallised-type intelligence and fluid-type. The former represents acquired knowledge and is often quantified by looking at vocabulary. Fluid-type concerns more unfamiliar and abstract cognition involving on-the-spot thinking.

The study estimates that 40 per cent of the variation in crystallised-type and 51 per cent of variation in fluid-type intelligence is accounted for by variation in SNPs, which are small changes in the nucleotide sequence in DNA.

This finding is similar to that of a 2010 paper in Nature that found another complex phenotypic trait, height, is associated with hundreds of genetic variants, each of which individually make a very small contribution.

However, precisely what the variations in the genome are that influence intelligence and, more poignantly, what they do, is unknown.

Some of the SNPs may be in genes, while others may be in non-protein-coding regions, and some may themselves be causally inefficacious but be linked to other variations that are. As such, the quest to reveal the biological underpinnings of intelligence are still very much in their early days.

“This is the first reported research to examine the intelligence of healthy older adults and, using a comprehensive genetic survey, we were able to show a substantial genetic contribution in our ability to think,” said Dr Neil Pendleton, who led the Manchester team in the Centre for Integrated Genomic Research.

“The study confirms the earlier findings of the research in twins. However, that research could not show which genes were or were not contributing to cognitive ability. Our work demonstrates that the number of individual genes involved in intelligence is large, which is similar to other human traits, such as height.

“We can now use the findings to better understand how these genes interact with each other and the environment, which has an equally significant contribution. With our collaborators, we will take this work forward to find the biological mechanisms that could maintain our intellectual abilities and wellbeing in late life.”