Only 4000 years ago? That is much more recent than I would have expected (I am familiar with humanity’s egalitarian roots prior to agriculture, but most everything I know about after the adoption of agriculture are societies that were either always hierarchical, or became hierarchical over time). How did they manage to escape notice from the more aggressively imperialist societies long enough to build such a city? How did they manage to police themselves in such a way as to avoid forming a dominance hierarchy themselves? They would have to have had some way of reliably identifying domineering individuals and acting against them in order to actually reverse the inequality trend like that. How did they ultimately fall?
Also, do you happen to have a link/citation for the academic paper that this article is referencing? I don’t even see the name mentioned in the article text - only the author and university.
Hierarchy in the Forest by Cristopher Boehm is literally about this. In short, we’ve always had some kind of “hierarchy”, but starting at about 3 million years ago, and becoming ubiquitous at around 300,000 years ago, we “inverted” the hierarchy so that domineering individuals were ostracized, and everybody else was more or less equal. In other words, we found a way to be egalitarian, despite our despotic roots as a species - and we did it for long enough to significantly impact the human genome.
Then the domineering individuals started to figure out how to undo this and form dominance hierarchies again, starting about 40,000 years ago.