Scientists have estimated for the first time the extent to which genes determine changes in intelligence across the human life course.
The study found that genetic factors may account for about 24 per cent of changes in intelligence between childhood and old age.
The findings also suggest that many of the genes that affect intelligence in childhood also influence intelligence in old age, according to the study published in Nature.
The study, by researchers at the Universities of Edinburgh and Queensland and Aberdeen suggests that the largest influence on changes in intelligence is probably environmental.
Identifying genetic influences on intelligence could help us to understand the relationship between knowledge and problem solving and an individual’s outcomes in life, and especially to understand why some people age better than others in terms of intelligence.
The researchers combined DNA analysis with data from people who took intelligence tests aged 11 and again aged 65 to 79.
The scientists examined more than half a million genetic markers in about 2,000 people to work out how genetically similar they were, even though they were not related.
The new findings were made possible because Scotland has a rich source of cognitive test data. In June 1932 and June 1947 intelligence tests were carried out on almost all children born in Scotland in 1921 and 1936, respectively. For the present study, about 2000 of these people were traced and re-tested in old age.
Until now, we have not had an estimate of how much genetic differences affect how intelligence changes across a lifetime. These new findings were possible because our research teams were able to combine a range of valuable resources. The results partly explain why some people’s brains age better than others. We are careful to suggest that our estimates do not have conventional statistical significance, but they are nevertheless useful because such estimates have been unavailable to date.
Unique data and new genome technologies combined with novel analysis methods allowed us to tackle questions that were not answerable before. The results also strongly suggest how important the environment is helping us to stay sharp as we age. Neither the specific genetic nor environmental factors were identified in this research. Our results provide the warrant for others and ourselves to search for those.
The study was supported by funding from the Age UK (Disconnected Mind project), the UK’s Biotechnology and Biological Sciences Research Council (BBSRC), The Royal Society, The Chief Scientist Office of the Scottish Government, the Wellcome Trust, Alzheimer's Research UK, the Australian Research Council, the National Health and Medical Research Council (Australia), and the Royal Society of Edinburgh.
The study was conducted within The University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology, part of the cross council Lifelong Health and Wellbeing Initiative (G0700704/84698), for which funding from the BBSRC, Engineering and Physical Sciences Research Council (EPSRC), The Economic and Social Research Council (ESRC) and MRC (Medical Research Council) is gratefully acknowledged.