Back in 1985, near the border between Argentina and Chile, mountaineers stumbled on a frozen body partially buried on Aconcagua, the world’s tallest peak outside of Asia. The boy, 6 or 7 years old, had been wrapped in cloth and buried surrounded by a number of small statues; he is believed to have been sacrificed in a ritual ceremony some five centuries ago by members of the Inca civilization. Recently, when Spanish researchers extracted and analyzed the boy’s DNA, they found he had a rare genetic code that has virtually disappeared from the population of modern South America.

At the time Spanish conquistadores arrived in 1532, the Inca Empire stretched along the South American coast from Ecuador to south-central Chile. According to Spanish chronicles, the Inca religion included the practice of capacocha, in which some of the healthiest and most beautiful young members of the population were chosen to become sacrifices to the gods. In many cases, these children were taken to high mountain peaks, considered to be closer to the realm of the gods. Once there, they were either killed or simply left to die of exposure.

In a new study, published last week in the journal Scientific Reports, a team of researchers explains that capacocha rituals “were performed during or after important events (death of an emperor, the birth of a royal son, a victory in battle or an annual or biennial event in the Inca calendar), or in response to catastrophes (earthquakes, volcanic eruptions and epidemics).” Their study focuses on one of these sacrificed children: a 6- or 7-year-old boy whose frozen, naturally mummified body was found high in the Andes in 1985.

Mummified remains of the boy. (Credit: Scientific Reports/University of Coyo/Gomez-Carballa et al)

After Spanish geneticists extracted mitochondrial DNA (which is passed from mother to child) from a small portion of the boy’s lung, they compared his genetic information with hundreds of thousands of samples held in a genetic database. They found only four matches: one individual of the ancient Wari Empire, dominant in the Andes from A.D. 500 to 1100, before the Inca heyday, and three modern-day people living in Peru and Bolivia. The Inca boy’s DNA identified him as part of a previously unknown offshoot of an ancient Native American lineage, which was one of the first to emerge among the humans who crossed the Bering Strait and spread into North and South America some 18,000 years ago.

Though the boy’s genetic profile is extremely rare today, the researchers say it was likely more common at the time of the Incas. As much as 90 percent of the native South American population perished after the Spanish conquest, mostly from epidemics of influenza and other diseases brought from the Old World; it makes sense that a great deal of genetic diversity would have been lost as well. As lead researcher Antonio Salas, a geneticist at University of Santiago de Compostela, told BBC News: “It is well-known that the effective population size was severely reduced at the arrival of the Spanish conquerors….An important amount of the variability of these populations could have disappeared at the time of this contact.”

The new study is the first to analyze the complete mitochondrial DNA of an Inca mummy. Salas now plans to sequence the boy’s complete nuclear genome, as well as the DNA of microbes found in his gut. According to him, the boy’s mummified body is extremely valuable for research purposes due to its well-preserved condition, as well as its “unique anthropological characteristics.”

In addition to the most recent DNA information, the Inca boy’s body has also yielded gruesome insight into the practice of child sacrifice among the Inca. Archaeologists found that he was strangled and died from a blow to the head. They also found evidence that he consumed achiote, a dye that can act as a hallucinogen, before his death. Similarly, a 2013 study of three other frozen mummies found in Argentina revealed that alcohol and drugs played a role in such child sacrifices. The strikingly well-preserved bodies of a 13-year-old girl and two younger children, a boy and a girl both 4 or 5 years old, were found buried in 1999 in a shrine near the summit of the Llullaillaco volcano. When an international team of researchers analyzed the chemicals found in the children’s hair, they found that all three had consumed alcohol and coca leaves (from which cocaine is extracted) in the months before their deaths.