Elaborate ritual killings such as being crushed under a newly built canoe and decapitation after being rolled off a house laid the foundations of class-based structures in modern societies, a new study of Austronesian cultures suggests.

Key points: Evidence of human sacrifice found in 40 out of 93 Austronesian cultures

Evidence of human sacrifice found in 40 out of 93 Austronesian cultures Victims were usually low status, instigators were elites such as priests and chiefs

Victims were usually low status, instigators were elites such as priests and chiefs Study suggests religious rituals played a darker role in the evolution of complex societies 12,000 years ago

The New Zealand-based study, published today in Nature, tracks the evolution of human sacrifice alongside the development of class-based societies across 93 cultures.

Co-author Joseph Watts, a doctoral student at the University of Auckland, said until 12,000 years ago humans mainly lived in egalitarian groups of hunter-gatherers.

However around that time hierarchical societies began to develop with the earliest examples a class-based system with wealth and power centred on a ruling elite.

"Our study shows in these early stages that human sacrifice might have helped to build and sustain the social class systems," he said.

Mr Watts said human sacrifice — the ritual and deliberate killing of an individual to appease a supernatural power — did this in two ways.

First it was used to punish taboo violations, demoralise the underclasses, mark class boundaries, and instil fear of social elites.

Further it minimised the "potential risk of retaliation by eliminating the victim" and allowed those responsible to shift the blame to the supernatural gods in whose name the sacrifice was made.

Geographic and socially diverse cultures studied

The team, which also included researchers from Australia, New Zealand and Germany, analysed 93 cultures from Madagascar in the west, to Rapa Nui in the east, and south to New Zealand — a region covering more than half the world's longitude and one-third of its latitude.

The social structures ranged from small egalitarian, kin-based societies to large, complex chiefdoms based in environments from tiny atolls to island continents.

For each of the cultures they recorded the presence or absence of human sacrifice and the level of social stratification.

They then developed models to determine whether human sacrifice and social hierarchies co-evolved.

Evidence of human sacrifice was found in 40 of the 93 cultures sampled (43 per cent). It was practiced in five of the 20 egalitarian societies (25 per cent), 17 of the 46 moderately stratified societies (37 per cent), and 18 of the 27 highly stratified societies (67 per cent) sampled.

Common occasions for human sacrifice in these societies included breaking of a custom or taboo, the funeral of a chief, and the consecration of a newly built house or boat.

Dark role of religious rituals

Mr Watts and the team found the victims were typically of low social status, such as slaves, and the instigators were of high social status, such as priests and chiefs.

Mr Watts said the method of sacrifice varied significantly.

"They didn't have the same kind of societies as the Aztecs and Mayans with temple structures, but had other elaborate rituals," he said.

These included burning, drowning, strangulation, bludgeoning, burial, being crushed under a newly built canoe, being cut to pieces, as well as being rolled off the roof of a house and then decapitated.

Mr Watts said the modelling showed human sacrifice "substantially increased the chances of high social stratification arising and prevented the loss of social stratification once it had arisen".

This suggested religious rituals played a "darker role" in the evolution of modern, complex societies, his team concluded, whereby "ritualised human sacrifice may have been co-opted by elites as a divinely sanctioned means of social control".

"Unpalatable as it might be, our results suggest that ritual killing helped humans transition from the small egalitarian groups of our ancestors, to the large stratified societies we live in today," the researchers said.