Is intelligence genetic?

Educational toys, brainy baby videos and flash cards — do these things help to develop intelligence? Or are the genes that you inherited from your parents the determining factor? The search for an 'intelligence gene' has intrigued scientists for decades.

Now, an international team of scientists have added weight to the argument that intelligence does have a genetic basis, but that it comes from multiple genes working together.

The team, led by Professor Ian Deary of the University of Edinburgh, compared the DNA of more than 3,500 people aged between 18 and 90. They were examining the patterns of half a million single nucleotide polymorphisms (SNPs), which are single base changes within a gene sequence. The study participants also took tests to assess both problem solving abilities (fluid intelligence) and long term memory skills (crystallised intelligence).

Data analysis was carried out using a novel genetic statistics procedure, called GCTA, developed by Professor Peter Visscher and his colleagues in Brisbane, Australia. They found that people who had high scores on the intelligence tests shared similar SNP patterns. Fifty-one percent of the variation in fluid intelligence and 40 percent of the variation in crystallised intelligence could be attributed to the trends in SNP patterns.

'It has been getting clearer and clearer that any genetic contribution to traits on which people differ — like height and weight — comes about from large numbers of gene differences, each with very small effects', said Professor Deary. He writes that this study 'is the first to show biologically and unequivocally that human intelligence is highly  polygenic and that purely genetic (SNP) information can be used to predict intelligence'.

This is the first time a genome wide association study (GWAS) has been used to analyse the genetic contribution to intelligence — previous work has focused on related individuals, and particularly twins. This removes any bias imposed by environmental factors, which in the past has resulted in contentious data interpretation.

Critics of the paper suggest that the results may not be representative of a larger area or different ethnicities due to the sample population being from one particular region. In an interview with the Los Angeles Times, Professor Deary said: 'We did not have exactly the same intelligence tests for each sample, which may have resulted in the underestimation of the effects of some genes'.

The next step is to carry out larger, more diverse GWAS analyses and use them to identify whether there are any specific genes involved.

The study is published in Molecular Psychiatry.