HEALTH
Intelligence is sexy, sperm study suggests
December 12, 2008
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There are few better ways of upsetting a certain sort of politically correct person than to suggest that the variation in intelligence among individuals is under genetic control.
That, however, is one implication of a paper by Rosalind Arden of King's College, London, and her colleagues that is about to be published in Intelligence.
And there are two more implications: that brainy people are intrinsically healthier than those less intellectually endowed and that intelligence is sexy.
The most surprising thing of all, though, is that these results have emerged from an unrelated study of the quality of men's sperm.
Arden is one of a group of researchers looking into the connections among intelligence, genetics and health. General intelligence (the extent to which measurable aspects of intelligence, such as linguistic facility or spatial awareness, are correlated in a given individual) is measured by psychologists using a value called Spearman's g.
Recently, it has been discovered that an individual's g value is correlated with many aspects of his health, up to and including his life- span.
One possible explanation is that intelligent people make better choices about how to conduct their lives. Alternatively (or in addition), it may be that intelligence is one manifestation of an underlying, genetically based healthiness.
Geoffrey Miller of the University of New Mexico, who is one of Arden's co-authors (and, as it happens, her husband), is among the evolutionary biologists who take this view, believing intelligence is such a reliable indicator of underlying genetic fitness that it has been chosen by members of the opposite sex over the millennia.
In the ensuing race to show off and get a mate, it has been exaggerated in the way that a peacock's tail is. Miller and his followers believe this process of sexual selection is the reason people have become so brainy.
Arden sought to test this idea in a way that excluded intelligent choice and got directly at any physiological correlations between intelligence and health. She chose sperm quality because it is both easily measured and about as far from intelligent choice as it is possible to imagine.
The relevant data had already been collected from former American soldiers enrolled in what was known as the Vietnam Experience Study. In 1985, almost 4,500 of these veterans volunteered for extensive medical and mental examinations. Some of them gave semen samples that were analyzed for the number of sperm per cubic centimetre, the total number of sperm in the ejaculate and sperm motility.
Arden found 425 cases suitable for testing her hypothesis, namely that their g values would correlate with all three measures of their sperm quality.
They did.
Brainy men, it seems, do have better sperm.
By implication, therefore, they have fitter bodies over all, at least in the Darwinian sense of fitness – the ability to survive, to attract mates and to produce offspring.
That is an important finding.
Up to now, biologists looked at "fitness" as a series of adaptations that are more or less independent of each other. Arden's work adds to the idea of a general fitness factor, f, that is similar in concept to g.
You could say g is one manifestation of f.
Unfortunately for the politically correct, Miller's hypothesis looks stronger by the day.
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