Samuel Bowles on group competition and relatedness as important factors in human cooperation

I thought I would go over some more of the details of this paper by Samuel Bowles in Science. I had briefly covered it in a recent post. The paper hasn't gotten as much coverage as I think it deserves so I'll try to spread the meme here.
My understanding of it, in a (long) sentence is that using the Price Equation for the evolution of altruism which takes into account the balance of a within-deme and between deme effect, and some estimates of group competition and within-group relatedness among modern hunter-gatherers, S. Bowles argues that with group competition and group relatedness being high enough (and he provides evidence that it may indeed have been) and with reproductive leveling due to monogamy (thereby reducing the amount of intra-group competition), human large scale cooperation can flourish.

Ok, that was a long sentence. Maybe a shorter way of saying this is that cooperation in humans is largely due to the relatedness of people within groups, along with the fact that conflict between groups was frequent enough and that reproductive leveling (monogamy) offset any possibility that within-group competition would increase too much.

Some questions:

Is it safe to make the assumption that the extent of group warfare we see in today's hunter-gatherers closely approximates what it was for most of our hominin evolution? - not so sure about that. Bowles actually notes that "even very infrequent contests would have been sufficient to spread quite costly forms of altruism. He also thinks that recurrent warfare would explain the frequent catastrophic mortality and very slow growth rates seen in human demographic history.

Is it safe to assume that levels of relatedness among individuals in groups was the same now in hunter-gatherers as it was for most of our hominin evolution? - I'm not very clear on how/where S. Bowles gets his data for relatedness among the hunter-gatherer groups and also why if they are so surprisingly high (just under that for cousins) no one else would have noticed this before.

I have always had a strong intuition that human cooperation is greatly strenthened by relatedness within groups and non-relatedness between groups and by group conflict. I had never thought of the importance of reproductive leveling. Sam Bowles gives these ideas which resemble the arguments of group selection) some empirical and theoretical strength.

These ideas have been passed around before, but it seems that the multilevel-selection approach to understanding human cooperation has gained much more acceptance recently.