Anyway, I think I've just confused the monogamy issue, read that article on Slimy Monogamy I linked to if you didn't, monogamy is an adaptation to circumstances where your offspring need a little more help.
Insofar as monogamy is the most commonplace strategy, it basically reflects the fact that children have a more difficult time thriving and maximizing their own breeding potential without significant parental involvement - without it, you're Veal.
That's what started the conversation, I did read that article.
I'm saying, monogamy doesn't sensibly fit into the h/g, agrarian societies, it's just there. The nine month gestation and years of direct parental supervision for the big brained child occurred long before sapiens-sapiens and erectus. Monogamy would've had to come into its own long before Homo, based on the physical necessity of the bigger brained biped coming out of the womb way too early. Based on the opinion of that article, which is a fairly popular opinion in human evolutionary theory.
We know that the father-son bond doesn't enter myth until well after agrarian societies are formed. The group is the father, initiates the son into adulthood well into the first agrarian settlements. The myth of father-son bond is what deceives us into believing monogamy existed to raise a child. We can't possibly comprehend the true egalitarian nature of these societies because we were brought up by one or two adults that had sole responsibility for us.
Monogamy exists before, during, and after the transition from group egalitarian sharing of parental duties to the family unit that emerges in post-industrial nations after the Second World War.