First direct biological evidence found for genetic contribution to intelligence

August 10, 2011

Scientists at The University of Edinburgh, U.K., have found.the first direct biological evidence for a genetic contribution to people’s intelligence.

The team studied two types of intelligence in more than 3,500 people from Scotland, England and Norway. They found that 40 to 50 percent of people’s differences in knowledge and problem solving skills could be traced to their genes. The study examined more than half a million genetic markers on every person’s DNA.

Previous studies on twins and adopted people suggested that there is a substantial genetic contribution to thinking skills. However, the new study is the first to test people’s DNA for genetic variations linked to intelligence.

Technical details of the study

The researchers conducted a genome-wide association study looking at over 500,000 common single nucleotide polymorphisms (SNPs), which are DNA sequence variations that occur when a single  nucleotide (A,T,C,or G) in the genome sequence is altered. They correlated genetic variation of participants’ performance on two types of general intelligence: knowledge and problem-solving skills.

The researchers found that up to half of individual differences in intelligence are due to genetic variants in linkage disequilibrium with SNPs. (Individuals often inherit rather long haplotypes (chunks) of DNA from one parent or the other, and some haplotypes themselves may also be inherited as a group. This is called linkage disequilibrium.)

The researchers found that a large proportion of the heritability estimate of intelligence in adulthood can be traced to genetic variants linked with common SNPs, confirming that at least 40–50% of individual differences in human intelligence are due to genetic variation.

The findings were made possible using a new type of analysis invented by Professor Peter Visscher and colleagues in the Queensland Institute of Medical Research, Brisbane.

Ref.: Ian Dreary, et al., Genetic associations for human intelligence difference, Molecular Psychiatry (in press) [DOI: MP.2011.85]