Senator Joe Biden did himself no favours when he “praised” his fellow presidential hopeful, Barack Obama, as “the first mainstream African-American who is articulate and bright and clean and a nice-looking guy”. It did not take long for the implication to sink in: does Senator Biden think that previous black candidates such as Jesse Jackson and Al Sharpton are inarticulate, dim, dirty or ugly?

Senator Biden has been charging around apologising to everybody, but what nobody really wants to admit is this: one of Senator Obama’s qualities is that he is handsome, and handsome politicians have a habit of getting elected. Economists have found evidence that voters prefer a pretty face in the UK, Australia, Finland, Germany and the US.

Researchers have to be careful when they observe simple correlations between subjective beauty and electoral success. Amy King and Andrew Leigh, who studied Australian elections, wondered whether the findings were driven by ageism or racism: perhaps (mostly white) voters see a black face and believe the face’s owner is both unattractive and unfit to govern. That sounds miserably plausible, but it is not driving the results: restricting analysis only to white politicians, or those in a narrower age band, produces similar estimates of a beauty premium.

It is not just politicians that we prefer to be beautiful. A number of studies, many involving the American economist Daniel Hamermesh, have found that “ugly” people earn less in many walks of life, from advertising to law. The beauty premium seems to apply even in professions where there is no reason to expect that beauty counts.

This is an intriguing pattern. The obvious explanations are either that employers like to be surrounded by pretty staff (and voters like to see pretty politicians on TV), or that we irrationally conflate beauty with useful qualities such as honesty or intelligence.

There is, however, another possibility: perhaps beautiful people are better at their jobs. There is no mystery as to why we want decorative Hollywood stars, but the same logic might apply to sales staff. Even a bureaucrat might be more persuasive if he or she is good looking, and who wouldn’t want persuasive employees instead of charmless ones?

Remember, too, that beautiful people have probably been treated well all their lives. This might affect abilities that have nothing, ostensibly, to do with appearance: if handsome kids get all the attention from teacher, why would they not do better at school?

One intriguing piece of economic research, from Markus Mobius of Harvard and Tanya Rosenblat of Wesleyan University, asked volunteers to guess how good they would be at solving maze puzzles under time pressure. Then the subjects were asked to solve as many as possible. Mobius and Rosenblat found that attractive people were more self-confident, but did not actually do any better. To the extent that we can generalise from this, perhaps the self-confidence of the beautiful helps them fool employers into paying more. Alternatively, perhaps self-confidence is an inherently useful trait in many walks of life, if not while solving little puzzles.

So perhaps there is more to the beauty premium than simple discrimination: beautiful people could well be genuinely more productive. But Professor Hamermesh devised a clever way to demonstrate that whatever lies behind our preference, our choices are based on skin-deep evidence. He showed that when candidates stood for election on more than one occasion, their chances of success rose simply when they used a more flattering photograph.

The electorate was surely the most rational in the world: the membership of the American Economic Association.