To a second approximation, humans have an astoundingly high level of parental investment than other species and also engage in alloparenting. This throws a proverbial monkey wrench into the first approximation.
Sure. But the "compromise on mate quality in return for resource commitment" strategy has always been fraught with what one might call coordination problems. The whole institution of marriage is basically a massive social engineering project meant to prevent these problems and align the interests of the partners. But marriage as an institution has grown far weaker: divorce, premarital sex, and children born out of wedlock are now seen as commonplace. And because of the increasing financial independence of women, they are less interested in compr...
http://theviewfromhell.blogspot.com/2012/09/toward-non-stupid-non-blank-slatey.html
The author gives a shout out to Less Wrong as a community with a perpetually skewed gender ratio, which is precisely the conditions under which polyandry appears to thrive.
Discuss. :)