On Hooking Up

The college hook-up culture is endlessly intriguing to me. This article attributes it to "the collapse of advanced planning, lopsided gender ratios on campus, delaying marriage, relaxing values and sheer momentum." The collapse of advance planning makes sense to me--with cell phones everything is immediate and spontaneous--no need to make a dinner date, just call your friends as you're walking into the dining hall. Delaying marriage makes sense to me--we are getting married later at least than we were in recent history, from what I've heard (Mary was 13 or 14, right?). Relaxing values, sure, whatever (at least relaxing social mores). But what's this about momentum? And what are the lopsided gender ratios? I know nothing about this as (not kidding) my esteemed (although not as esteemed as some) undergrad institution accepted students according to a strict 50-50 ratio (the better for marrying you off, my dear).