The influence of genes on exceptional mental ability:
A new "mega-analysis" of 11,000 twin pairs, aged between 6 and 71, has helped to plug that gap. The results suggest that genes exert a significant influence on exceptional cognitive ability, similar in magnitude to their influence on the normal range of intelligence. The findings challenge versions of the "discontinuity hypothesis" – the idea that the relative contribution of nature and nurture changes for exceptional ability.
Claire Haworth and colleagues, of the newly-established Genetics of High Cognitive Abilities (GHCA) consortium, combined data from six studies, involving twins from four countries – the UK, Netherlands, Australia and United States. Combining so much data altogether allowed them to restrict their analyses to participants in the top 15 per cent for intelligence performance, whilst still maintaining enough power for statistical tests.
By comparing intelligence differences between pairs of identical twins (who share all their genes) and non-identical twins (who share half their genes like normal siblings), the study showed that genetic differences explained approximately half the variation found in high intelligence, whilst shared environmental factors - those experienced by both twins in a pair, such as education and parenting style - explained just 28 per cent of the variation. The remaining influence is down to unique environmental influences (experienced by one twin but not the other) and other unknown factors.
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