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DNA from centuries-old Incan mummy provides scientists with clues to genetic diversity

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Archaeologists and geneticists have sequenced the genome of a boy sacrificed 500 years ago during an Incan ritual in the Andes, finding a previously unidentified lineage that hints at genetic diversity before the Spanish landed in the Americas.

Spanish geneticists extracted the DNA of a mummy found in the icy heights of Aconcagua, the world’s tallest mountain outside Asia, near the border of Argentina and Chile. The mummy, of a seven-year-old boy who was sacrificed by the Inca, showed a DNA signature that has virtually disappeared in modern South Americans.

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The researchers ran the mummy’s DNA through a database of genetic code and found only four people with a corresponding trace: three modern people from Peru and Bolivia and one ancient person from the Wari empire , a Peruvian civilization that predated the Inca by several hundred years.

The researchers suggested in a study published in the journal Scientific Reports that the gene pool changed so dramatically due to the consequences of colonization.

“Up to 90% of native South Americans died very quickly,” lead researcher Antonio Salas, of the University of Santiago de Compostela, told Science magazine. “You can imagine that a lot of genetic diversity was lost as well.”

Studying the DNA of ancient people, mummified or not, can help “reconstruct …colonial politics and migration and change”, Lars Fehren-Schmitz, a geneticist and anthropologist at the University of California, Santa Cruz, told the Guardian.

Fehren-Schmitz noted that although diseases likely killed more Native Americans in the 16th century than any other factor – and in doing so removed genes from the population accordingly – the different ways in which Europeans colonized the Americas were also reflected in the gene pools.

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Fehren-Schmitz, who was not involved in the study, noted that the mitochondrial DNA analyzed in the Aconcagua mummy was passed along by the boy’s mother, and thus revealed only some of who he was, genetically.

European DNA appears in relatively high proportions around South America, but is rare in mitochondrial DNA.

“In North America there were mass migrations, with men, women and children,” Fehren-Schmitz said. “In South America, the Spanish brought specialists, soldiers, priests. It was men.”

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He added that the study generally supports other hypotheses about how quickly the original colonizers of the Americas – ancient people who crossed the frozen Bering strait from Asia – managed to spread down through the continents. The lineage subgroup in the Aconcagua mummy’s DNA dates back to more than 18,000 years ago, the researchers found.

“It’s only one individual, but it’s a specific sub-lineage in a restricted geographic area,” Fehren-Schmitz said, referring to the relative isolation of the southern Andes. A relatively rare DNA signature, like that of the Aconcagua boy, could suggest that the genomes of groups of Americans became more unique over long phases of isolation.

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“It’s another brick in the wall,” he said, to the idea that “people came to the Americas quite rapidly and then groups stopped in isolated places, creating their own demographic complexities”.

In 2011 Fehren-Schmitz co-wrote a paper assessing a much larger dataset of ancient and modern genomes, and found that Native Americans suffered a sizable population loss in the 1500s.

The Aconcagua mummy is special for its extraordinary state of preservation, Salas said, which was caused by the high altitude and freezing temperatures of its burial site. The boy was killed in a sacrificial ritual called capochoca, which the Inca performed to make offerings to the gods.

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The children were often young, high-born and “special”, Vanderbilt University archaeologist Tom Dillehay told the Guardian. When climbers discovered it in 1985, the Aconcagua mummy wore two tunics and was flanked by gold, silver and shell statuettes.

Capochoca was performed for important events, either religious or relating to the Inca emperor – who was considered a descendant of the sun. The children were taken up into the mountains to be killed.

Most of the children chosen for capochoca “were not physically traumatized, and were often given some kind of herb or alcoholic drink”, such as the Peruvian corn drink chicha, to put them into a deep sleep or coma, Dillehay said.

Little is known of who the Aconcagua boy was, but he does not appear to have died in peace. Vomit stained his clothes red and archaeologists found achiote , a dye which can act as a hallucinogen, in his intestines. He was strangled and died from a blow to the head .

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The children were taken into the mountains because the Inca considered them “sacred landscapes”, Dillahey said, in part because their “deities were stacked vertically, top to bottom”.

A child entombed on the slopes of Aconcagua, near one of the mountain roads along which the Inca carved their empire, would thus rest as close as the Inca could get to their highest gods.

“They looked up to the heavens in the same way we still do,” Dillehay said. “In a sense, that is.”

guardian.co.uk © Guardian News and Media 2015

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