http://healthland.time.com/2012/05/29/the-ancient-sexual-revolution-that-may-have-spurred-human-monogamy/

My main takeaway from this article is that apparently (and this is only the researchers' hypothesis) early human ancestors would mate wildly like our monkey friends in the wild - where a handful of alpha males would have their way with any of the females, leaving the child-rearing to the females.

Low-ranked males, who had no hope of physically overcoming the dominant members of their groups, instead began providing extra food to certain females, to curry sexual favor. These females responded by remaining faithful to their breadwinning males. That change in behavior favored the reproductive success of these monogamous couple

Meaning, the females would reward "beta" behavior with faithfulness - this led to more successful child-rearing between the couple rather than just the stranded female. This is exactly what bluepillers want and expect.