Societies scale up through added hierarchy levels, not mere population growth

Evidence

Human societies did not increase in scale simply by including more and more people. The scaling-up process was accomplished in a special way: increasing hierarchical complexity by adding levels of administrative control. At each step of the process, lower-level units had to cooperate with each other, so that together they could better compete against rival coalitions. — Norenzayan, Ara, Big gods - how religion transformed…, 475