The Puzzle of Human Ultrasociality: How Did Large-Scale Complex Societies Evolve?
After a long and turbulent history, the study of human cultural evolution is finally becoming comparable to the study of genetic evolution, with human history the counterpart of the biological fossil record. One of the most remarkable products of cultural evolution has been an increase in the scale of human societies by many orders of magnitude. Today, the great majority of humans live in complex societies, which can only exist due to extensive cooperation among large numbers of individuals. Ultrasociality, the ability of humans to cooperate in large groups of genetically unrelated individuals, presents a puzzle to both evolutionary and social theory. Although much theoretical effort has been devoted to understanding the evolution of cooperation in small-scale groups (hunter-gatherers living in societies of hundreds to a few thousand individuals), the same cannot be said about the next phase of human evolution, the rise of complex societies encompassing tens and hundreds of millions of people. Evolutionary biologists, political scientists, anthropologists, and others have proposed a multitude of theories to explain how complex societies evolved. However, scientific study has suffered from two limitations. First, with a few exceptions, theories have relied on verbal reasoning; formal models tend to focus on the evolution of cooperation in small groups, whereas the transition from small- to large-scale societies has been mostly neglected. Second, there has been no systematic effort to compare theoretical predictions to data. Human ultrasociality has evolved repeatedly around the world and across time, reflecting both common selection pressures and the unique contingencies affecting each case. An enormous amount of archaeological and historical information exists but has not been studied from an evolutionary perspective. Thus, explicit models that will yield specific and quantitative predictions are needed as well as databases of the cultural evolution of human ultrasociality. Furthermore, a research program combining explicit models with empirical testing of predictions is not only an academic endeavor. Understanding conditions that either promote or inhibit human ultrasociality is highly relevant for addressing the challenges of large-scale cooperation and conflict in the modern world. Published in the Strungmann Forum Reports Series.