Has History Proved Eysenck Right About Genes and IQ?

Philip Corr, The Conversation, March 10, 2016

Hans J. Eysenck, one of the most famous and infuriating British psychologists of the 20th century, would have been 100 years old this month. While Eysenck pioneered behaviour therapy (paving the way for the acceptance of cognitive behavioural therapy) and argued for the necessity of evidence-based medicine and meta-analysis, in later years his reputation was eroded by his hugely controversial writings on race and IQ and his largely unproductive forays into astrology, and research on smoking.

Eysenck’s thoughts on IQ and genetics were also hugely unpopular. He argued that general intelligence (a broad measure of mental capacity) had a genetic basis, which is associated with a wide variety of life outcomes, including socioeconomic difference. When coupled with the race-IQ controversy, all of this was explosive stuff and Eysenck was regularly criticised for his views and even, on one occasion, physically attacked. In 1973, a female protester punched him in the face at a London School of Economics event.

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In a recent paper, Hagenaars and colleagues reported on a study of over 100,000 people showing that there are shared genetic influences on intelligence, a range of diseases (including coronary artery disease, stroke, Alzheimer’s disease, schizophrenia, autism and depression), as well as body mass index, infant head circumference and brain size.

These findings point to “pleiotropic” effects, that is, when one gene influences two or more seemingly unrelated traits. In this case, cognitive function, physical health and psychiatric disorders.

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Hagenaars and colleagues’ work is important, not so much for trumpeting the relevance and predictive power of cognitive tests, as well as reaction time measures of intelligence (which it does), but for revealing to us a number of significant things. First, mental and physical health are closely related–something that Eysenck believed all of his life. Second, the ability to do various cognitive tests may be a good indicator of general physical, as well as psychological well-being. And third, it should now be possible to determine what is truly caused by social disadvantage (for example, poverty) and what is properly to be attributed to common genetic influence on intelligence, health and wealth.

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Although Eysenck conducted one of the earliest statistical genetic studies on twins, and he worked closely with experts in genetics, he did very little empirical work on the association between genetics and intelligence. His influence came in the form of his ideas and writings–and from his championing of this most unpopular scientific cause.

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