This is a claim so extraordinary you should at least have linked some obscure paper from a *-Studies department.
Every human has their own hierarchies. Hierarchies of need, of goals and of peers (this is basically each individual's social hierarchy). But when these people form large groups they are somehow able to blank the slate and not make it hierarchical?
All mammals that form groups instinctively form hierarchies and constantly validate their own and other's position in it (any dog owner will know first-hand). Arguably the first multi-celled organism formed a hierarchy and pretty much every animal with a few Neurons has Serotonin receptors, which can be described as a pathway to continuously re-order its hierarchy of needs.
The only way in which anything social isn't hierarchical is if you look at a tiny tiny cross-section. Otherwise any "egalitarian" and "flat" organization just swapped one way to determine a hierarchy for another. As a case in point, the Liberal model of the 19th century was a project to replace an aristocratic hierarchy (based on attributes that were no longer a good fit) with a competence hierarchy. This was often called egalitarian, but practically it was just a more adapted way of forming a hierarchy.
We are so adapted to hierarchies that 6-month olds understand physical dominance and 3-year olds easily form more complex hierarchies based on social support, resources etc.
edit:
Ironically calling other people "rock-dumb" is a way to signal ones own place in the hierarchy.