Edinburgh Napier University

  Social hierarchy is a pervasive element of modern societies, yet almost absent before the advent of agriculture during the Neolithic transition. Despite evidence supporting hierarchy as a product of evolution, it is hard to explain the mechanisms which drove this evolution. For instance, the evolution of followers appears as a paradox because followers receive fewer resources than leaders. The “iron law of oligarchy” proposes that the key to the Neolithic transition lies in the role of leaders in collective decision-making. First, leaders would emerge in response to an increase in group size because leaders speed up decision-making and facilitate coordination. Then, leaders would use their newly acquired influence to bias opinions and group decisions to impose inequality that benefits themselves. This theory has the benefit of explaining the origin of both beneficial and despotic sides of leaders. Yet, its investigation has been limited because of the lack of a formal description of (i) how individuals change with time and (ii) how individuals take collective decisions. Thus, we propose the evolutionary iron law of oligarchy, which reinterprets the iron law in evolutionary terms. We reduce leaders and followers to their capacity to influence and we claim that describing the evolution of this trait under the environmental changes observed at the Neolithic transition is sufficient to explain the emergence of helpful and despotic leaders. To investigate this claim, we build individual-centred models simulating consensus formation — how individuals take collective decisions —and evolutionary dynamics — how individuals change with time. On one hand, our results show that the evolutionary iron law of oligarchy is a viable scenario, which can unify previous theories explaining either the beneficial or despotic side of leaders. On the other hand, we developed a mechanistic model of the iron law of oligarchy which can apply across a range of scenarios, and which show under which conditions the iron law of oligarchy would apply. Finally, our results demonstrate that the iron law of oligarchy goes beyond political sciences and is underwritten by the laws of Darwinian evolution. Understanding the factors driving the emergence of hierarchy and despotism will open new perspectives to design better forms of governance.