The idea that sex ratios alter sexual behavior is well-established. Analysis of demographic data from 117 countries has shown that when men outnumber women, women have the upper hand: Marriage rates rise and fewer children are born outside marriage. An oversupply of women, however, tends to lead to a more sexually permissive culture. The same holds true on college campuses. In the course of researching our book Premarital Sex in America, my co-author and I assessed the effects of campus sex ratios on women's sexual attitudes and behavior. We found that virginity is more common on those campuses where women comprise a smaller share of the student body, suggesting that they have the upper hand. By contrast, on campuses where women outnumber men, they are more negative about campus men, hold more negative views of their relationships, go on fewer dates, are less likely to have a boyfriend, and receive less commitment in exchange for sex.Found at When Boys Fail
How does this "man shortage" affect marriage rates? For now, at least, a college degree is a status marker.
As just about everyone (from Dennis Prager to pickup artists) has figured out by now, women tend to want men of high status, men they look up to — literally, in terms of height, and figuratively, in terms of social standing, income, and education. If women systematically outpace men on these status markers — as they are beginning to — they will have to compete for men they deem suitable at a less-than-even ratio. There’s nothing we can do about this that I can think of, but it will not be good for marriage.