Exercise is good for you. A new paper by Andrew Clark shows that children who play sport go on to get better jobs and earn more. This corroborates earlier research by Michael Lechner.

Why? The standard answer is that sport either inculcates or reveals useful non-cognitive skills: teamwork, discipline and so on. Mens sana in corpore sano as they said in the old public schools, and probably still do.

There might, however, be a darker side to sportier people's higher earnings, which Jeremy Celse of the University of Montpellier points out in a recent paper (pdf).

He ran a simple experiment in which pairs of subjects were given small sums of money, with the subjects then told how much their counterpart had received. He found that people who played sport were almost twice as likely as non-sportsmen to say they were unhappy when they learnt that their counterpart had received more. 'Practicing a sport increases significantly the probability for a subject to report a decrease in his satisfaction after being exposed to unflattering social comparisons' he says.

What's more, sporting people were almost twice as likely to cut their partner's gift, even at the expense of making themselves worse off.

This hints at a dark side of sport. It is, generally, a zero-sum game, with winners and losers. Sportsmen transfer this mindset into other aspects of life. They are therefore more likely to feel bad when they compare themselves to others, as they feel like losers. To avoid this feeling, they take measures which might hurt themseleves. This happens even in cases, such as Mr Celse's experiment, where everyone is in fact a winner, in the sense of being better off than they were before.

Herein lies a worry. It could be that sporting people's higher earnings arise not merely from their positive non-cognitive skills, but from these darker impulses. Not only does their desire to avoid feeling like a loser spurs them to work harder, but - worse still - they'll be more prepared to hurt others in order to avoid that feeling. They thus have the sharper elbows necessary to climb greasy poles (is this a mixed metaphor). As Gore Vidal (a quarterback at West Point) said, 'it is not enough to succeed; others must fail.'

It is, I suspect, no accident that a lot of prominent US business people were active sportspeople in their youth.