The boy’s pattern of genetic variations placed him in a population called C1b, a common lineage in Mesoamerica and the Andes that dates all the way back to the earliest Paleoindian settlements, more than 18,000 years ago. But C1b in itself is very diverse — as its members spread throughout Central and South America, smaller groups became isolated from one another and started developing their own particular genetic variations. As a result, C1b contains many genetically distinct subgroups. The Aconcagua boy’s genome didn’t fit into any of them. Instead, he belonged to a population of native South Americans that had never been identified. Salas and his team dubbed this genetic group C1bi, which they say likely arose in the Andes about 14,000 years ago. They detail their findings today in Scientific Reports.
When Salas combed through genetic databases, ancient and modern, he found just four more individuals who appear to belong to C1bi. Three are present-day people from Peru and Bolivia, whereas another sample comes from an individual from the ancient Wari Empire, which flourished from 600 to 1000 C.E. and predated the Inca in Peru. Clearly, C1bi is extremely rare today, but the fact that it has now popped up in two ancient DNA samples suggests that it could have been more common in the past, says Andrés Moreno-Estrada, a population geneticist who studies the Americas at Mexico’s National Laboratory of Genomics for Biodiversity in Irapuato and was not involved in the current work. If you sample just one or two individuals, “what are the chances that you pick the rare guy?” he says. “Most likely, you’re picking the common guy.”