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The end of nature versus nurture

Since John Locke wrote of ‘tabla rasa’ in his essay of 1690 and more recently Francis Galton of ‘Hereditary Genius’ in 1869, scientists, philosophers and social commentators have argued long and hard on the issue of Nature vs Nurture. It has been a polemic and inevitably a politicised argument. Through twin studies, behavioural genetics and other approaches, scientists have variously argued the proportion of our ‘genius’ which is due to either pedigree or poverty - or their interaction. Now for the first time, a milestone scientific study confirms unequivocally - based on measured genetic data – that a large proportion of intelligence is inherited. Moreover, the data show inherited intelligence is the result of small contributions by lots of genes rather than a big effect of just one or two genes. In other words, a substantial proportion of individual differences in human intelligence is due to genetic variation. The study made the discovery after analysing half a million genetic markers in a large sample of 3,500 older people in Scotland and England. The data were checked against a separate group of older people in Norway. And it was led by scientists from the University of Edinburgh funded by Age UK, using a new type of analysis, invented by Professor Peter Visscher and colleagues in Brisbane. It is called the Disconnected Mind.

These unique data reveal that the proportion of intelligence that is down to genes is 40% for crystallised intelligence and 51% for fluid intelligence. Crystallised intelligence refers to learning, knowledge and skills that are accumulated over a lifetime. This type of intelligence tends to increase with age. Fluid intelligence is the ability to reason quickly, think abstractly and deal with complex information around us. It tends to decline with age.

The significance of these findings is hard to appreciate. In the past, the view existed that it might never be possible to separate out, in a quantitative sense, the various proportions of nature and nurture. And not only that, those scientists who searched for ‘intelligence genes’ had been unable to find them or had their methodology or findings derided on the grounds of racism or other prejudice. The study too is not without its criticisms but it represents a watershed development in our understanding of one of the most intractable issues in science. It has generated huge interest in the world’s scientific press and for good reason. Not only does it represent a paradigm of excellence in the quality of its science but it also opens the way for a clearer, less equivocal understanding of the role of those modifiable factors in the environment which influence how we maintain good cognitive function as we age.

Age UK is proud to have supported this study. Good science is never quick. Findings take years, even decades to emerge and even longer to influence thinking, the view of society and policy change in critically important areas. The decline of our mental function as we age is one of these areas, feared by millions and affecting increasing numbers in our ageing society. As a result of this study, we are one step closer to real solutions which will enable present and future generations to age healthily and well.

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