The Puzzle of Human Sacrifice

Harvey Whitehouse in New Scientist:

Today’s small-scale societies tend to favour infrequent but traumatic rituals that promote intense social cohesion – the kind that is necessary if people are to risk life and limb hunting dangerous animals together. An example would be the agonising initiation rites still carried out in the Sepik region of Papua New Guinea, involving extensive scarification of the body to resemble the skin of a crocodile, a locally revered species. …

With the advent of farming, … [and their] larger populations, … new kinds of rituals seem to have provided that shared identity. These were generally painless practices like prayer and meeting in holy places that could be performed frequently and collectively, allowing them to be duplicated across entire states or empires. …

A puzzle, however, is that many of these early civilisations also practised the brutal ritual of human sacrifice. This reached its zenith in the so-called archaic states that existed between about 3000 BC and 1000 BC, and were among the cruellest and most unequal societies ever. In some parts of the globe, human sacrifice persisted until relatively recently. The Inca religion, for example, had much in common with today’s world religions: people paid homage to their gods with frequent and, for the most part, painless ceremonies. But their rulers had divine status, their gods weren’t moralising and their rituals included human sacrifice right up until they were conquered by the Spanish in the 16th century. …

Instead of helping foster cooperation as societies expanded, Big Gods appeared only after a society had passed a threshold in complexity corresponding to a population of around a million people. … something other than Big Gods allowed societies to grow. … that something was the shift in the nature of rituals from traumatic and rare to painless and repetitive. … human sacrifice was used as a form of social control. The elites – chiefs and shamans – did the sacrificing, and the lower orders paid the price, so it maintained social stability by keeping the masses terrorised and subservient. … the practice started to decline when populations exceeded about 100,000. … 

Piecing all this together, here is what we think happened. As societies grew by means of agricultural innovation, the infrequent, traumatic rituals that had kept people together as small foraging bands gave way to frequent, painless ones. These early doctrinal religions helped unite larger, heterogeneous populations just enough to overcome the free-riding problem and ensure compliance with new forms of governance. However, in doing so they rendered them vulnerable to a new problem: power-hungry rulers. These were the despotic god-kings who presided over archaic states. Granted the divine right to command vast populations, they exploited it to raise militias and priesthoods, shoring up their power through practices we nowadays regard as cruel, such as human sacrifice and slavery. But archaic states rarely grew beyond 100,000 people because they, in turn, became internally unstable and therefore less defensible against invasion.

The societies that expanded to a million or more were those that found a new way to build cooperation – Big Gods. They demoted their rulers to the status of mortals, laid the seeds of democracy and the rule of law, and fostered a more egalitarian distribution of rights and obligations. (more)

It makes sense that complex intense rituals can only work for small societies, while larger societies need simpler rituals that everyone can see or do. It also makes sense that moralizing gods help promote cooperation. But I’m not convinced that we understand any of the rest of these patterns. The human sacrifice part seems to me especially puzzling. I can sort of see how it could serve a function, but I don’t see why that function would be especially effective in societies of population 10-100K.