Ah, spring! Love is in the air as brides and grooms anticipate the day on which -- surrounded by friends and family -- they will bow to the economic forces that have brought them together. Love may be the basis of marriage, but it is the market, to a large extent, that brings brides and grooms together and shapes their lives as married couples.

Princeton University alumna Susan Patton caused a stir recently with her open letter urging young female students to lock down an Ivy League man while they have easy access to such high-quality marriage candidates. Whatever you think of this advice in terms of gender politics, one thing is certain: She's got the economics all wrong. It's those Princeton women who hold all the power.

Back when Ms. Patton married in the early 1980s, well-educated women faced a very thin marriage market (that is, a market with few 'buyers' and 'sellers,' as it were). They had to select a husband from a small set of highly sought-after, well-educated men. At that time, men earned significantly more than women. Women's desire to marry up in terms of education made economic sense. In most marriages of the time, husbands earned the high wages, and wives (who earned less regardless of their education) focused their energy on the family.

For women like Ms. Patton, who attended college in the 1970s, the incentive was to find a husband during their years at school, where the marriage market was relatively thick with educated single men -- even if that meant compromising on other qualities they might have wanted in a husband. Later in these women's lives, they knew the market would thin and they would have to set their 'reservation value' -- the minimum set of qualities a man must possess as husband material -- at a lower level.

But over the past four decades, economic factors have changed the marriage market in a way that benefits highly educated women.

Between the ages of 25 and 40, for every 100 men with a college education there are now 132 college-educated women. That may sound like the marriage market for educated women has become even thinner, which it has for women who insist on finding a better-educated husband. But many women now are looking for other qualities.

For example, the gender imbalance has led many educated women to marry much younger men. These men are game because they prefer to have a wife who is older and more economically successful over a wife who is younger and less able to provide financial stability. The women, in turn, get a young, virile spouse.

The educational imbalance has also promoted marriages in which women hold a greater share of the household bargaining power. Among currently married couples with a difference in education levels, according to the Pew Research Center, the wife is much more likely to be better educated than the husband (that is, in 28% of marriages vs. 19% of marriages). So husbands have a greater incentive to share decision-making with their wives. Men who don't are at a much greater risk of divorce: Their wives can support themselves if necessary, and the husbands will lose a good deal of their household income if the breadwinning wife leaves.

This educational divide between men and women is also one of the reasons why female infidelity has increased in recent decades. Researchers at Tilburg University in the Netherlands, led by Joris Lammers, looked at the behavior of more than 1,500 professionals and found that women who are higher up the corporate ladder are more likely to cheat (just as higher-status men are). And since men who are financiallydependent have more to lose if they leave unfaithful wives, female infidelity is less likely to lead to divorce when the woman makes more.

Finally, at a time when women outrank men in education and income, it no longer makes economic sense for a woman to marry up in terms of education. The most economically productive marriages for professional women are ones in which husbands are freer to care for the needs of the family while the women focus on their lucrative careers.

In her letter to Princeton women, Ms. Patton acknowledges that these young women could delay marriage and 'choose to marry a man who has other things to recommend him besides a soaring intellect.' On this point, she is right. In fact, economic theory predicts that this is exactly the decision that many Princeton women will make -- not because they have to but because they can.