Every year, more women than men become college-educated. The disparity is already prevalent across North America and Europe, and the trend is beginning to spread across the world more widely. At the University of Texas at Austin where I teach, the sex ratio is 54 percent women to 46 percent men. This imbalance may not seem large at first blush. But when you do the math it translates into a hefty 17 percent more women than men in the local mating pool. Speculations about reasons range widely. They include the gradual removal of gender discrimination barriers and women’s higher levels of conscientiousness (relative to men’s) that translate into better grades and superior college app qualifications. Whatever the causes turn out to be, the disparity is creating a dramatic and unintended mating crisis among educated women.

We must look deeply into our mating psychology to understand the far-reaching consequences of the sex ratio imbalance. Women and men both have evolved multiple mating strategies; some of each gender pursue casual hook-ups, some committed partnerships. Some alternate at different times of their lives, and some do both simultaneously. And although a few social scientists deny the data, research overwhelmingly shows that men harbor, on average, a greater desire for sexual partner variety. Men experience more frequent sexual thoughts per day, have more sexual fantasies involving multiple partners, and more readily sign up for online dating sites for the sole goal of casual sex. So, a surplus of women among educated groups caters precisely to this dimension of men’s sexual desires because the rarer gender is always better positioned to get what they want on the mating market. In places like large cities in China, with their surplus of men, women can better fulfill their desires while many men remain frustrated and mateless. Context matters. For every surplus of women in places like Manhattan, there exist pockets where men outnumber women, such as schools of engineering or the software companies of Silicon Valley. But when there are not enough men to go around, women predictably intensify their sexual competition. The rise of the hookup cultures on college campuses and online dating sites like Tinder, Adult Friend Finder, and Ashley Madison is no coincidence.

Gender differences in sexual psychology are only part of the problem. Additional elements of the mating mind exacerbate it. A key cause stems from the qualities women seek in committed mateships. Most women are unwilling to settle for men who are less educated, less intelligent, and less professionally successful than they are. The flip side is that men are less exacting on precisely these dimensions, choosing to prioritize, for better or worse, other evolved criteria such as youth and appearance. So the initial sex ratio imbalance among educated groups gets worse for high achieving women. They end up being forced to compete for the limited pool of educated men not just with their more numerous educated rivals, but also with less educated women whom men find desirable on other dimensions.

The depletion of educated men worsens when we add the impacts of age and divorce to the mating matrix. As men age, they desire women who are increasingly younger than they are. Intelligent, educated women may go for a less accomplished partner for a casual fling, but for a committed partner they typically want mates their own age or a few years older, and at least as educated and career-driven. Since education takes time, the sex ratio imbalance gets especially skewed among the highly educated—those who seek advanced degrees to become doctors, lawyers, or professors, or who climb the corporate ladder post-MBA. And because men are more likely than women to remarry following divorce and to marry women increasingly younger than they are—three years at first marriage, five at second, eight at third—the gender-biased mating ratio skews more sharply with increasing age.