The Economics of the Pill and Sexuality:

The logic of evolutionary psychology says that women should be choosy about who they have sex with, because pregnancy in the wrong circumstances is extremely costly—but the logic of a woman who has control of reliable contraception is quite different. The preferences that evolution has shaped still exert powerful influence on our instincts, and many women remain extremely choosy and refuse to have sex outside marriage. But others, once armed with the pill, decided they could afford to have a little more fun.

The choosy ones are unlucky: the existence of other women who are a little freer with their favors weakens the bargaining power of the Madonnas, and means that men have less incentive to marry. Some men will not bother at all, feeling that they can get all they want from a playboy lifestyle. Or they may delay marriage until middle age, cutting down on the pool of marriageable men and increasing male bargaining power.

As we have seen, the rational response is for women to go to college, bringing them both better prospects in the job market and better prospects in the marriage market. Meanwhile, the more capable women become of looking after children by themselves, the less men need to bother. It’s a textbook case of free-riding: with highly-educated women in excess supply, men have realized that they can get sex, and even successful offspring, without ever moving too far from the La-Z-Boy chair and the potato chips. Statistics seem to bear this out. There are nowadays four US women graduating from university for every three men, and this is not a particularly American phenomenon: in 15 out of 17 rich countries for which the data are available, more women are graduating than men. The most educated men in the United States were born just after the second world war and graduated in the mid 1960s—male graduation rates dipped after that, and have not yet returned to that peak. The rational choice perspective suggests it is probably not coincidental that this decline set in roughly when women got hold of the contraceptive pill.