Inequality Through the Ages

Economists are often interested in inequality as a modern phenomenon. They collect evidence on the distribution of wealth between the rich and the poor, both in the present and over the past two or three centuries (largely since the advent of industrial capitalism). This is important for evaluating and monitoring present-day levels of inequality, for learning about the historical causes and consequences of inequality, and for examining the effects of inequality on economic performance, for example in the form of gross domestic product (GDP) growth.

In a seminar at Pompeu Fabra University (UPF) on 24 May, Prof. Peter Turchin (University of Connecticut, Complexity Science Hub Vienna) invited his audience to consider a broader view.  He began by arguing that, since approximately 10 million years ago, human structural equality has followed a zig-zag pattern. In the first stage, the strong hierarchical nature of the groups formed by our ancestral primates is likely to have led to high degrees of structural inequality, which remained the case until more recognisable forms of human society emerged.

Source: Presentation by Prof. Peter Turchin, 24 May 2017

Approximately 200,000 to 100,000 years ago (depending on one’s definition of “human”), a large part of humanity was organised into foraging bands, and by 10,000 years ago, into small farming communities. These societies would have been more egalitarian than the social groups of their ancestral primates, due to their increased requirement for cooperation and relatively flat social structure. However, such egalitarian groups rarely grew beyond a typical size of several hundred or at most a few thousand individuals. One explanation for this is that humans can only maintain face-to-face cooperation with around 100 to 200 individuals, and therefore effective cooperation broke down once egalitarian groups grew too large.

To overcome this threshold, human societies required hierarchy. Specifically, adopting a hierarchical structure means that each individual needs to maintain face-to-face links with only his superior and his subordinates, creating a societal unit that can be scaled up indefinitely. Such hierarchical structures, combined with surplus resources generated by advances in agriculture and private property rights, allowed humans to form chiefdoms and archaic states numbering millions of individuals in the past 10,000 years. Due to their hierarchical nature, these societies were also characterised by higher levels of structural inequality, which is evident from a historical record of slavery, human sacrifice, unequal rights for commoners and elites, deification of rulers, and large wealth disparities.

When we look at modern societies, two important differences with these archaic states stand out. First, in many instances modern nation states are even larger than the societies described above, with tens or even hundreds of millions of members. Second, although present societies do exhibit varying levels of economic inequality, the severe forms of structural inequality described above have largely disappeared. Moreover, the explicit aim of many modern government structures is to benefit the public at large, for example by codifying human rights and democratic ideals. This raises an important question: how do such pro-social norms become dominant in human societies?

Source: Presentation by Prof. Peter Turchin, 24 May 2017

Prof. Turchin emphasises that the ultrasocial behaviour required to sustain societies of many millions comes at a significant evolutionary cost to the individual members of those societies. For example, volunteering for military service involves a large sacrifice of one individual’s chances of survival for the benefit of genetically unrelated individuals. In view of this, he proposes that the rise of ultrasocial norms can only be explained by an evolutionary mechanism operating between societies.

According to Prof. Turchin, the turning point came with the advent of the Axial age approximately 3,000 years ago. In part due to advances in technology — including the use of horses to travel longer distances, and the increased use of composite bows and iron — military competition between societies intensified. In this environment, the largest and most cohesive societies are likely to prevail, for example because mustering a large army is a collective action problem that requires a very high degree of intrasocietal cooperation.

This meant that evolutionary pressures favoured the selection of societies with prosocial cultures, including those with norms and institutions that constrained rulers in order to promote the public good. This period also saw the gradual disappearance of many structural forms of inequality as societies grew, including human sacrifice, the deification of human rulers, and eventually slavery. At the same time, new world religions, whose central messages often emphasised prosocial norms, started to spread.

Two opposing forces were therefore at play. On the one hand, a society expanding in size needs to increase the depth of its hierarchy to accommodate more individuals, which tends to increase structural inequality. On the other hand, competition between societies favours more cohesive and cooperative societies with lower levels of inequality. With the advent of the Axial age, military pressures meant that the latter force began to dominate the former, ultimately yielding the (relatively) prosocial societies much of the world lives in today.

This hypothesis generates predictions that can be tested against alternative theories. For example, opposing theories could hold that inequality only started to decline in the modern age instead of following a zig-zag pattern over millions of years, that mass religion generates inequality through oppression instead of being prosocial, or that military conflict destroys cooperation and decreases social scale instead of promoting ultrasocial norms. With a view to distinguishing between such rival hypotheses, Prof. Turchin is involved in building a global historical database of cultural evolution, Seshat, with the aim of collating data from diverse sources on the sociopolitical organisation of human societies from the earliest times up to the present.

Ultimately, research undertaken in this field is likely to provide important insights for the inequality debate in economics, as well as other economic issues. For example, if they are correct, the arguments summarised above have implications for development theory and the mechanics of how individual nation states become more successful, prosocial societies. They also have implications for the cooperation required between nation states to address global issues such as climate change.


Turchin, P.  (2015) Ultrasociety: How 10,000 Years of War Made Humans the Greatest Cooperators on Earth. Beresta Books.