How science is helping us understand human sacrifice

Homo sapiens in nearly every part of the world has practiced human sacrifice at some point over at least five millennia, often killing females in fertility rites or for burial alongside powerful males.

But new research enabled by DNA analysis and other scientific advances has challenged assumptions about the identity of sacrificial victims, at least among the Maya of Central America.

Between 900 and 1,400 years ago, the Maya regularly sacrificed boys—particularly twins or close male relatives—according to a study published in June in the journal Nature.

The findings are based on the ancient DNA of 64 children who had been deposited in an underground cistern at the site of Chichén Itzá, a city built on Mexico’s Yucatán Peninsula.

For the ancient Maya, being sacrificed was considered a privilege, so these boys—most of whom were between the ages of 3 and 6—were likely given up willingly by their families, according to Rodrigo Barquera, an immunogeneticist at the Max Planck Institute for Evolutionary Anthropology in Germany and co-author of the recent study.

A possible explanation for the sacrifices lies in Maya lore. According to the culture’s written traditions, “Hero Twins"—both male—traveled to the underworld to avenge their father, a twin himself, who was killed by the lords of the underworld. Sacrifices of two male children were likely part of a ritual that helped the Maya honor this part of their mythology and belief system.

At the distance of millennia, these and other ritual killings appear barbaric. But to the cultures that carried them out, human sacrifices served myriad purposes, including fulfilling a universal desire to manage the uncontrollable world in which they lived.

“We think of this as such a bizarre practice, something very unusual and unexplainable, but three-quarters of societies did it," according to Peter Turchin, an evolutionary scientist at the Complexity Science Hub, a Vienna-based research organization, who wasn’t involved in the research.

For the most part, ritual killings fell into one of two categories.

The first was what anthropologists called a retainer sacrifice, when servants or consorts, for example, were killed to accompany someone who had died—usually a member of the elite—into the great beyond.

It was particularly prevalent among members of the African Kingdom of Dahomey, which persisted until roughly the beginning of the 20th century; during the Shang Dynasty of China some three millennia ago; and in Egypt between about 3100 and 2900 B.C. King Djer, a pharaoh who ruled during ancient Egypt’s first dynasty, had more than 500 retainer sacrifices surrounding his tomb in Abydos.

The other form was the sacrifice of captives or community members to placate, please or ask favors of gods and ancestors. “You’re supplying the divine world with something valuable in order to get something in return," said Glenn Schwartz, a professor of archaeology at Johns Hopkins University. “It’s often discussed in the literature as a gift-giving enterprise."

The Aztec, who mostly postdated the Maya and were famous for cutting out the hearts of prisoners atop pyramids as an offering to their gods, didn’t even have a word for human sacrifice.

“The word they always used for these ceremonies was debt payment," said Davíd Carrasco, a historian of religions at Harvard University.

Children were believed to be among the best emissaries to the gods because in many cultures they were considered purer than adults, and thus better able to communicate with the spirit world.

The ancient Carthaginians sacrificed their infants and buried the ashes in urns at special seaside burial grounds, perhaps to engender safe voyages across the Mediterranean.

Centuries ago, the Inca drugged and sacrificed their children in a ritual known as capacocha to appease the gods during times of crisis, such as a drought or disease, according to Angelique Corthals, a forensic anthropologist at John Jay College of Criminal Justice in New York.

“The Inca were trying to control that event by offering the most precious thing that they had," she said. Some of these children were brought high atop a dormant volcano in the Andes, where their bodies ended up mummified and exceptionally preserved because of the cold atop the peak.

In one of the largest known examples of child sacrifice, the Chimú killed more than 100 boys and girls in prehispanic Peru some 500 years ago. Hundreds of baby llamas were killed too.

Experts have interpreted the Chimú sacrifice as “a very desperate act to communicate with the gods during a period of extreme climate change," said Brenna Hassett, a biological anthropologist and lecturer at the University of Central Lancashire in the U.K. It followed a time of heavy rainfall and flooding from an El Niño event, concurrent with an invasion threat from the nearby Inca.

But inferring motives, or even distinguishing ritual killings from executions with nothing more than visual examinations of bones or burials is challenging.

The contents of a tomb can offer hints—such as the presence of objects for use in the afterlife called grave goods or the positioning of bodies in relation to one another—but now a new wave of studies is using genetic analysis to shed light on archaeological mysteries.

DNA analysis and other tools enable anthropologists to discern where a person was from, the quality of their diet and health and their sex—something previously impossible for children and a key to the discovery of the Maya boys.

“While you can determine sex from adult bones, the result of hormone changes during puberty, these changes are lacking in children," said Barquera’s co-author, Christina Warinner, a biomolecular archaeologist at Harvard.

Barquera and his group analyzed the petrous bone—a dense part of the skull’s temporal bone that preserves DNA well—from 64 children found in the Maya cistern.

In addition to learning that the children were male, they found identical genomes in the different bones, revealing the pairs of identical twins. The DNA also revealed genetic continuity between these boys and the modern-day Maya living in the area today, underscoring that those being sacrificed had been chosen from within the local community near Chichén Itzá, rather than being outsiders. 

The findings run counter to historical narratives passed down by Spanish officials and priests that Mesoamerican cultures tended to sacrifice enslaved captives.

Radiocarbon dating of the bones showed the boys weren’t all killed at once, hinting, Warinner said, that the sacrifices might have been related to a cyclic ritual ceremony. Isotopic analysis showed that most of the boys shared the same diet, suggesting they were raised together and deliberately prepared for sacrifice, Barquera added.

“It’s such an exciting time to be doing archaeology," said Nawa Sugiyama, an anthropologist from the University of California, Riverside, who wasn’t involved in the Maya work. “The level of detail with which we’re able to reconstruct these rituals has really opened up our ability to be there and relate to these families and communities."