[wordup] Sperm, intelligence and genetic fitness

[Adam Shand]

Source: http://www.economist.com/science/displayStory.cfm?story_id=12719355

Balls and brains
Dec 4th 2008

The quality of a man’s sperm depends on how intelligent he is, and  
vice versa

THERE are few better ways of upsetting a certain sort of politically  
correct person than to suggest that intelligence (or, rather, the  
variation in intelligence between individuals) is under genetic  
control. That, however, is one implication of a paper about to be  
published in Intelligence by Rosalind Arden of King’s College, London,  
and her colleagues. Another is that brainy people are intrinsically  
healthier than those less intellectually endowed. And the third, a  
consequence of the second, is 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.
Ms Arden is one of a group of researchers looking into the connections  
between intelligence, genetics and health. General intelligence (the  
extent to which specific, measurable aspects of intelligence, such as  
linguistic facility, mathematical aptitude and 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 lifespan. One possible explanation for this is  
that intelligent people make better choices about how to conduct their  
lives. They may, for example, be less likely to smoke, more likely to  
eat healthy foods or to exercise, and so on.

Alternatively (or in addition) it may be that intelligence is one  
manifestation of an underlying, genetically based healthiness. That is  
a view held by many evolutionary biologists, and was propounded in its  
modern form by Geoffrey Miller of the University of New Mexico, who is  
one of Ms Arden’s co-authors (and, as it happens, her husband). These  
biologists believe intelligence, as manifested in things like artistic  
and musical ability, 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 arms race to show off and get a  
mate it has been exaggerated in the way that a peacock’s tail is. This  
process of sexual selection, Dr Miller and his followers believe, is  
the reason people have become so brainy.

Hitting the g spot
Ms Arden sought to test this idea in a way that excluded intelligent  
choice and got directly at any correlations between intelligence and  
health that operate at the physiological level. She chose sperm  
quality because it is both easily measured and about as far from  
intelligent choice as it is possible to imagine—and because the  
relevant data had already been collected.

Her retrospective “volunteers” were former American soldiers enrolled  
in what was known as the Vietnam Experience Study. In 1985 almost  
4,500 veterans of that war volunteered for extensive medical and  
mental examinations. Some of them gave semen samples that were  
analysed for sperm concentration (ie, number of sperm per cubic  
centimetre), sperm count (ie, total number of sperm in the ejaculate)  
and sperm motility.

Ms Arden found 425 cases where samples had been collected and analysed  
from unvasectomised men who had managed to avoid spilling their seed  
during the collection process and had answered all the necessary  
questions for her to test her hypothesis, namely that their g values  
would correlate with all three measures of their sperm quality.

They did. Moreover, neither age nor any obvious confounding variable  
that might have been a consequence of intelligent decisions about  
health (obesity, smoking, drinking and drug use) had any effect on the  
result. 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, namely the ability to survive, to  
attract mates and to produce offspring. That is an important finding.  
Hitherto, biologists have tended to disaggregate the idea of fitness  
into a series of adaptations that are more or less independent of each  
other. This work adds to the idea of a general fitness factor, f, that  
is similar in concept to g—and of which g is one manifestation. To him  
that hath, in other words, shall be given. Unfortunately for the  
politically correct, Dr Miller’s hypothesis looks stronger by the day.