If we go back to the ancestral environment, what characteristics would men and women have been looking for? Since a woman needed the physical strength to bear and rear the baby, youth and health – for which beauty is a reliable indicator – would top the list of male desires. We can imagine that a father’s role in raising children, primarily, was to provide and protect: perhaps the most able hunters would have been in most demand as long-term partners, or the strongest fighters, or the canniest at making political alliances. All these attributes would have translated into high status. And in modern times, we have a very reliable indicator of high status: wealth.

On the African savannah, then, our rational male forebears wanted young and beautiful partners while our rational ancestors down the maternal line would have preferred high-status males. Have these preferences survived to the present day? Folk wisdom would certainly say so.

In the song Summertime from Gershwin’s opera Porgy and Bess, there’s a reason why Bess soothes the baby with the line “Your daddy’s rich and your mamma’s good lookin’ ” rather than the other way round. And how often do you hear of a 26-year-old Chippendale marrying an 89-year-old heiress?

As ever, economists aren’t satisfied with folk wisdom. And fortunately, there’s a data source to settle all (well, almost all) controversy on the matter: internet-dating success rates.

Economists have been studying internet dating just as assiduously as they study speed-dating, and have found that men attract a lot of replies if their internet dating ads claim a high income. The situation is reversed for women: if a woman claims a high income in an internet dating ad, she will receive fewer replies than if she had claimed a modest income. It is official: rich men are a turn-on and rich women are a turn-off.

Perhaps you don’t think internet-dating responses are really a window on to the soul. You may be right, but there are other sources of evidence. If, as George Gershwin, evolutionary biologists and internet daters suggest, women are particularly interested in netting themselves a rich man, then presumably we should find lots of women in places where there are lots of rich men: that is, in the cities.

Since men aren’t as interested in marrying someone with high earning power, the good marriage prospects in the cities are less of an attraction to men than women. As rents rise, it will be the unskilled men who give up and move to the country before the unskilled women do – or who never bother to move to the cities in the first place.

The economist behind this idea is Lena Edlund, of Columbia University. She explained the implications to me. First, men would always be in shorter supply in cities than in the countryside.

In 44 out of 47 countries studied by Edlund, they are. (In the three exceptions, the sex ratios are equal in the cities and the countryside.) Within the US, you find the same pattern in the big cities. In Washington DC, women outnumber men nine to eight.

In New York, there are 860,000 men between the ages of 20 and 34, but there are 910,000 women. There are more men, though, in rural states: Alaska, Utah and Colorado.

Another implication of Edlund’s theory is that since unskilled men are most likely to stay away from cities, unskilled urban jobs that could easily be done by either sex would tend to be done by women. (Waitressing? Secretarial work? There is nothing inherently, or historically, female about these jobs.) And we would also expect to find that the higher male incomes go, the greater would be the supply of – how to put this? – spare women. That is exactly what Edlund finds in a detailed study of Sweden: areas with high male salaries are areas where a lot of women live, especially young women.

Consciously or not, plenty of women seem to have decided they would rather compete for scarce, wealthy males than move where the males are poorer but more plentiful.

Manhattan’s women may constantly grumble about the lack of marriageable men in the city, but it is their rational choice not to relocate to Alaska.

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