'Intelligence genes' prove elusive

New research aimed at uncovering some of the genetic variation which contributes to human intelligence has revealed that IQ (intelligence Quoteint) is the result of interactions between many different genetic and environmental factors, according to a report published in the journal Genes, Brains and Behaviour last week.

In the hunt for genetic variations that influence IQ, a team of researchers led by Robert Plomin of the Institute of Psychiatry in London used verbal and non-verbal reasoning tests to assess the intelligence of 7000 seven-year-olds. They compared the genetic code of those who scored highly to those who scored lowly in order to identify which, if any, genetic variants were more common in either group.

Despite using such a large sample size, the researchers identified 37 different versions of just six genes that appear to be linked to intelligence. They estimated that together these variants account for just 1 per cent of the total genetic variation related to intelligence, suggesting that hundreds of genes contribute to intelligence, each with only a small effect.

Professor Plomin said: 'If the biggest [genes] only account for 1 per cent of the variance [in intelligence], there's a long way to go. The most striking result is there are no large effects'.

However this does not mean that intelligence has nothing to do with genes. Previous studies on twins and adopted children suggest that 50 per cent of intelligence is down to our genetic makeup and 50 per cent is the result of the environment in which we grew up. Given the evident complexity of the trait, pinpointing those environmental and genetic components which contribute to intelligence will likely be a long and difficult process.

'Intelligence is a function of the way the brain is put together, and at least half of our genome contributes in some way or another to brain function, which means that in order to build a human brain, you need thousands of genes to work together', New York University psychologist Gary Marcus told New Scientist.