Sex and the single black woman

http://www.economist.com/node/15867956

IMAGINE that the world consists of 20 men and 20 women, all of them heterosexual and in search of a mate. Since the numbers are even, everyone can find a partner. But what happens if you take away one man? You might not think this would make much difference. You would be wrong, argues Tim Harford, a British economist, in a book called “The Logic of Life”. With 20 women pursuing 19 men, one woman faces the prospect of spinsterhood. So she ups her game. Perhaps she dresses more seductively. Perhaps she makes an extra effort to be obliging. Somehow or other, she “steals” a man from one of her fellow women. That newly single woman then ups her game, too, to steal a man from someone else. A chain reaction ensues. Before long, every woman has to try harder, and every man can relax a little.