An explanation consistent with The Dawn of Everything
Human societies are inherently unequal. Inequality arises at root from biology, since individuals have different levels of social, athletic, etc. ability. Groups who lack meaningful accumulated wealth or property (such as children on the playground, or hunter-gatherer tribes) still have a social pecking order, leaders, etc. which exists whether or not designated by formal titles.
"Primordial democracy" therefore seems like hand-waving romanticism. Neolithic tribesmen lived nasty, brutish, and short lives in which 30-40% of males died by violence, per modern anthropological studies. "Equality" was a function of absolute poverty, in that everyone in your sample owns zero tangible wealth, property, or capital.