It seems to me that polyandry is intrinsically blank-slatey. A good first approximation of male vs. female reproductive strategy is that males seek to optimize the net quality of their mates, while females seek to optimize the mean quality of their mates. In the former strategy, there is never anything to be lost by adding another mate, while in the latter strategy, there certainly is.
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.
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. :)