I got an interesting tweet today from Elizabeth McLaughlin, whose 40percentandrising.com website tracks the rise of the female breadwinner:

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McLaughlin was responding to my mini op-ed in The New York Times, which argued that the falling marriage rates among under-30, college-grad women are a byproduct of a shortage of men in the college-educated dating pool (or what I call “the man deficit”). McLaughlin’s response is one I usually hear not from women but from men—i.e. the reason so many successful women are still single is they’ve been spending too much time on careers or on building nest eggs and not enough on dating and on men. In other words, it’s their fault.

Before I attempt to disprove this, let me acknowledge that there are indeed some men who are afraid to date smart women and others who are uncomfortable with wives or girlfriends outearning them. This mindset does seem to be fading—according to Pew Research, 30% of married women were primary breadwinners in 2007 versus 4% in 1960—but I’m not so naive as to believe it no longer exists.

The problem with attributing the declining marriage rates among young, female college grads to a greater focus on careers is two-fold. First, it assumes that millennial women are working harder than women who graduated from college 20 years ago. As someone who graduated from college in the 1990s and who has many 40-something female friends who worked extremely hard to get where they are today (including my wife), let’s just say I’m dubious.

Second, McLaughlin’s argument implies that the high marriage rates and low divorce rates in Silicon Valley—one of the few well-populated areas where college-grad men now outnumber college-grad women—are a fluke. In fact, there’s a ton of scholarly research demonstrating a strong correlation between sex ratios and marriage rates and between sex ratios and divorce rates. Santa Clara County, situated in the heart of Silicon Valley, has 12% more college-educated men than women age 22 to 29, whereas Manhattan has 39% more such women than men. Not coincidentally, 33% of the Santa Clara County women in that cohort are married and only 4% divorced versus 13% married and 7% divorced in Manhattan. Bottom line: The women of Silicon Valley are in a better position to demand commitment from men.