Stabbed, burned, drowned, strangled, bludgeoned, buried alive. These are only a few of the many ways that humans were ritualistically sacrificed throughout history. These people lost their lives in deference to a higher deity for a range of reasons—to ensure fertile crops, to follow masters to the afterlife, to bring rain.

The victims, however, were often of a lower class, slaves or captives from adjacent communities, and their deaths were frequently drawn out. The perpetrators of the acts were usually the social elite. These facts all hint at a possible darker motivation for human sacrifice: keeping some people at the top of the social ladder and others at the bottom.

This idea, known as the Social Control Hypothesis, was popularized in the late 1990s with the study of human sacrifice in early American cultures. Now a new study, published today in Nature, adds to the evidence that the hypothesis might be correct. Using statistical methods, a team of New Zealand researchers has shown that human sacrifice could have played a crucial role in cementing the layers of social status that gave rise to the eventual formation of many complex societies.

In these early cultures, sacrifice was a tool to terrorize the masses, says the study’s lead author, Joseph Watts, a graduate student at the University of Auckland. “It provided a supernatural justification for punishment,” he explains on his website.

The new study focuses on Austronesian cultures, a group of peoples that share a common root language originating in Taiwan. Throughout history, these people diversified and spread across Southeast Asia and Oceania, as well as to Madagascar. Many practiced human sacrifice, including nearly half of the 93 cultures Watts and his colleagues studied.

The mode and rituals around the ceremonies, however, vastly differed between the people practicing them.

For instance, on Shortland Island, which is near Papua New Guinea, a human sacrifice would be necessary upon the building of a common house. The victim would be placed in a hole and then crushed under the weight of a pole dropped into the pit.

Another group, the Melanau people of northern Borneo, would tie the hands of several slaves to the mausoleum of their recently deceased master. Abandoned there, the slaves would die of exposure and, supposedly, serve their master in the afterlife.

The researchers studied such accounts using historical records primarily from the 19th century. They were careful to only examine periods of time before outsiders introduced major world religions, such as Christianity or Islam, and modernized the communities.

Using linguistic information, the researchers created a phylogenetic tree—a complicated branching map of the type more often used to show the interconnectivity of species through time. But instead of creatures, they mapped out the evolution of Austronesian cultures.

They also ornamented the tree with two key details for each community: the degree of social stratification and whether or not the people practiced human sacrifice. Then came the math.

The researchers applied a statistical method to their tree to suss out patterns and examine the relationship of social stratification and human sacrifice through time. This determined whether cultures that had formed a social elite also practiced human sacrifice and vice versa. The method also helped the researchers to directly sort out cause and effect, determining which came first—social status or human sacrifice.

What the results show is that human sacrifice may have helped bolster differences in social status. If a society practiced human sacrifice, it was unlikely for social stratification to diminish and for people to return to a society in which everyone was a social equal. The model also showed that the practice of human sacrifice may have helped to hasten the development and separation between various layers of social status.

The results add support to the idea that human sacrifice instilled fear and at the same time demonstrated the power of the elite, Watts says. This system could have been an early means to build and maintain power, which was a step to the development of complex societies and more formal political systems.

The model also suggests that human sacrifice was not all that important in making the transition from an egalitarian society to a stratified one. That’s because, Watts says, “if human sacrifice is being used at all to maintain social power, there has to be power to start off with.”

“These effects aren’t overwhelmingly strong, but they are consistent,” says Mark Pagel, an evolutionary biologist at the University of Redding who wasn’t involved in the study. Although the results do support the role of human sacrifice in social stratification, he says, there could be exceptions to the pattern.

Human sacrifice, however, could have been an effective technique for maintaining power in some societies, Pagel says. “Imagine you lived in a society that is highly stratified, and the ‘winners,’ or so-called elite, of that society would, on certain occasions, just grab someone off the street and sacrifice them,” he says. It’s an effective tactic to warn people that the elite are powerful and to get them to toe the line. “It doesn’t mean that sacrifice is just or right, but it does serve to control a society,” he says.

Watts notes that many of the rituals surrounding sacrifices seemed to aim for the utmost gore—with some ceremonies delaying the moment of death for many hours. “It’s not just a matter of killing efficiently. There's more to it than that,” he says. “The terror and spectacle [of the act] was maximized.”

One example of such a ritual in the Ngaju society was described by Hans Schärer in Ngaju Religion: The Conception of God Among a South Borneo People: "It begins towards sunset and lasts until sunrise. All the participants dance around the slave and stab him with sacred spears, daggers, swords and blowpipes… About sunrise he receives the coup de grace and collapses dying in his own blood."

The question still remains whether the results of this study extend beyond the Austronesian people. Motivations for human sacrifice widely varied across cultures, yet many showed similar links to social hierarchy, Watts says.

There was a tomb found in Eastern China, for instance, that scientists determined was the grave of an aristocrat buried with nearly four dozen victims of human sacrifice along with a trove of precious artifacts. And ancient Egyptians, of course, are known to have similarly buried slaves alongside deceased rulers.

However, in Central and South America, “the Maya, Aztec and Inca, and other New World societies celebrated the capture and sacrifice of rulers and other high status individuals,” says John Verano, an anthropologist at Tulane University. Among these peoples, human sacrifice may have served a different purpose.

For many societies, though, “social stratification was probably one of the first steps in social complexity,” Watts says. “In these early stages, human sacrifice was serving a crucial role in building and maintaining social structures.”