then hard disagree about your hard disagree about my hard disagree - most any psych/sociological experiment will show we're fundamentally social/cooperative. in fact it's hard to imagine our species surviving if we were fundamentally self-interested (basic biology couldn't give 2 farts about the individual, it's built on diversifying the gene pool to ensure adaptability and thus survival) - and supposedly we can live in a fairly egalitarian tribe of up to about 75 or so people (maybe even 200+)
it seems like our big social shift was cultivating grain which allowed us to harvest then store it - at that point, the tribe not only needs 'soldiers' to help defend from outside forces, but also 'police' to protect assets from inside