Intelligence could be measured with a swab of saliva, or drop of blood, after scientists showed for the first time that a person’s IQ can be predicted just by studying their DNA.

In the largest ever study looking at the genetic basis for intelligence, researchers at the University of Edinburgh and Harvard University discovered hundreds of new genes linked to brain power.

Previous studies have suggested that between 50 per cent and 75 per cent of intelligence is inherited, and the rest comes through upbringing, friendship groups and education. That figure was calculated by studying identical twins who share the same DNA, therefore any differences in IQ between them must be non-genetic.

But nobody knew which were the ‘smart genes.’

Now by studying the genetic data from more than 240,000 people, scientists have found 538 genes which are linked to intelligence.

Researchers were even able to predict intelligence just based on a person’s DNA, a breakthrough which could potentially help doctors to diagnose impaired cognitive ability, or allow children to be given an tailor-made education based on their innate abilities.