Peter Turchin sees human egalitarianism following a complex Z-curve, zigging to greater inequality during the pre-axial period, and then zagging back toward equality in the last few thousand years:
The starting point for approaching this question is what is sometimes called as the ‘U-shaped curve of despotism’ in human evolution. We know that our closest relatives, the chimps and gorillas, live in fairly ‘despotic’ or inegalitarian societies. The chimps, for example, establish linear dominance hierarchies, in which alpha males get better food and greater access to females. We don’t know for sure whether human ancestors also lived in similarly inegalitarian societies, but it seems likely.
In contrast, as was argued by Christopher Boehm in Hierarchy in the Forest: The Evolution of Egalitarian Behavior, human hunter-gatherers, who lived in small-scale societies before agriculture, were fiercely egalitarian. High degree of equality does not simply happen because hunter-gatherers are poor and cannot accumulate much wealth (chimps also cannot accumulate wealth). No, equality requires active maintenance. People living in small-scale societies possess numerous norms and institutions designed to control ‘upstarts’ — those who attempt to set themselves as alpha-males so that they can gain control of an unfair share of resources (including females). The sanctions deployed against upstarts range from gossip and ridicule to ostracism and, ultimately, assassination.
Thus, until c.10,000 years ago, before agriculture was invented, the human evolutionary trend was that of increasing egalitarianism. The adoption of agriculture, however, enabled the rise of large-scale societies organized as states and empires with highly unequal distributions of power, wealth, and social status. In other words, the trend to greater equality reversed itself. What accounts for this U-turn? Why did humans allow inequality to develop?
The answer apparently is that the U-turn was a side effect of the transition from small-scale to large-scale societies. Small-scale societies of hunter-gatherers were integrated by face-to-face sociality. Such a diffuse, non-centralized social organization was well-suited to maintaining egalitarian ethos. However, once the size of cooperating group increases beyond 100–200 people, even gigantic human brains are overwhelmed by the demands of face-to-face sociality (this is the argument made by Robin Dunbar). Shifting from diffuse, uncentralized social organization to hierarchical organization (as chains of command) allowed evolution to break through the upper limit on society size imposed by face-to-face sociality. A member of a hierarchically organized group needs to have face-to-face interactions with only a few individuals: a superior and several subordinates. Such links can connect everybody in a group of arbitrarily large size. The group size grows by adding additional hierarchical levels.
So far so good, but the great downside of hierarchical organization is that it inevitably leads to inequality. Once you allow a leader to order everybody around, he will use the power to feather his nest. This is sometimes known as the iron law of oligarchy.
I have argued elsewhere that conditions of endemic warfare between human groups create enormous selection pressures for larger group size (“God is on the side of big battalions”) and for effective (which means centralized) military organizations. Under such conditions, emergence of centralized military hierarchies becomes virtually inevitable. The result is the rise of increasingly complex centralized societies — chiefdoms, complex chiefdoms, and archaic states.
As Bellah notes, archaic states were characterized by enormous fusion of power in the person of the ruler. Almost invariably the rulers of such states were ‘divinized’, that is, considered to be gods as well as kings. They had literally the power of life and death over their subjects. One frequent characteristic of early centralized societies was the practice of massive human sacrifice. This naked pursuit of power and voracious appetite for consuming resources is reflected in such characterizations of rulers as a land shark who ‘eats’ island (in Hawaii), or a big rat that gobbles people’s millet (in archaic China).
Thus, although highly effective on the battlefield, a centralized military hierarchy has several drawbacks as a general way of organizing societies. A society cannot really be held together by force alone. Worse, great inequities resulting from rapacious military chiefs and their retinues alienate large segments of the population. As a result, early despotic chiefdoms and archaic states were very fragile and frequently did not outlast their founders.
The tension between the human preference for equitable outcomes and the need for centralized hierarchy brought about the “legitimation crisis of the early state” (this idea was borrowed by Bellah from Jürgen Habermas). The tension became particularly acute during the Axial Age (c.800–200 BCE), for reasons discussed in my review of Bellah’s book and other publications. One central argument in Bellah’s book is that the new world religions and philosophies that arose during the Axial Age began the long job of building more equitable societies. A large part of this evolution was imposing limits on the power of rulers and replacing power based on naked force with legitimate authority.