Whether it be to appease the gods for a plentiful harvest, mark important events like the death of a leader or the construction of a house or boat, or promise success in the upcoming war, human sacrifice has played a vital role in the emergence of inherited class systems.

A new study from the University of Auckland's School of Psychology, the Max Planck Institute for the Science of Human History in Germany and Victoria University has found that the priests and rulers who sanctioned such ritual killings had another motive: to control, terrorize and impress lower ranking subjects.

"Religion has traditionally been seen as a key driver of morality and cooperation, but our study finds religious rituals also had a more sinister role in the evolution of modern societies," explained Joseph Watts, lead author of the study.

To learn more about how human sacrifice was facilitated by social stratification - or how unequal or hierarchical ancient cultures were, researchers examined historical data from a total of 93 traditional Austronesian societies. Overall, researchers found 40 out of the 93 cultures included in the study practiced some form of ritualistic human killing.

Austronesians are believed to have originated in Taiwan, before moving across the Indian and Pacific oceans, from Madagascar to Easter Island and as far south as New Zealand. Among the many methods of sacrificial killing used in these cultures were burning, drowning, strangulation, bludgeoning, burial, being cut to pieces, crushed beneath a newly-built canoe or being rolled off the roof of a house and decapitated. Generally, victims were of low status, such as slaves.

"By using human sacrifice to punish taboo violations, demoralize the underclass and instill fear of social elites, power elites were able to maintain and build social control," Watts added.

Each of the 93 cultures studied were classified as one of three main groups: egalitarian, meaning rank and power was not passed down through generations; moderately stratified, meaning societies allowed for inherited status, but without pronounced social classes; and highly stratified, meaning there were strict class differences, social mobility was restricted and stature was mainly inherited.

This, researchers said, revealed 67 percent of the 27 highly stratified cultures were likely to practice human sacrifice, while only 25 percent of the 20 egalitarian societies examined were likely to do so. And of the 46 moderately stratified societies, only 37 percent exhibited practices of human sacrifice.

"Human sacrifice provided a particularly effective means of social control because it provided a supernatural justification for punishment," explained Professor Russell Gray, co-author of the study. "Rulers, such as priests and chiefs, were often believed to be descended from gods and ritual human sacrifice was the ultimate demonstration of their power."

What's more is researchers were able to test whether sacrifice preceded or followed changes in social status.

"What we found was that sacrifice was the driving force, making societies more likely to adopt high social status and less likely to revert to egalitarian social structure," co-author Quentin Atkinson concluded.

Their findings were recently published in the journal Nature.