The population suffered a ninety percent contraction and it is just possible that one key subgroup was particularly vulnerable as well. Either way that contraction knocked out populations and particularly those settled with a pretty common gene profile. These are also likely the settlements that march up mountains to sacrifice a child.
It also informs just how much DNA can be lost. Actually i would like to understand just how DNA diversity expands as a population expands without any serious intermarriage if at all. I do not think it can but we see ample diversity from small populations to the point of generating apparent races.
Back breeding may well be highly effective at raising up an otherwise dormant gene complex.
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The DNA of a boy sacrificed by the Inca suggests a lost, ancient lineage
Scientists can only find three modern people that match his DNA.
FIONA MACDONALD
16 NOV 2015
http://www.sciencealert.com/the-dna-of-a-boy-sacrificed-by-the-inca-suggests-a-lost-ancient-lineage
Researchers have sequenced the genome of a young boy who was sacrificed as part of an Incan ritual around 500 years ago, and his DNA suggests that the Andes were a lot more genetically diverse before the Spanish arrived in the Americas at the end of the 1400s.
The body of the seven-year-old boy was found in 1985 near the top of Aconcagua – the world’s tallest mountain outside of Asia – and had been naturally mummified by the cold. Now geneticists have found that his genome contained a DNA signature that seems to have pretty much disappeared from modern South Americans, but at one point may have been incredibly common.
The boy was part of an Incan ritual sacrifice known as capacocha, which involves taking children up to the top of the mountain and either killing them or leaving them to die. There are mummified remains of these sacrifices throughout the former Incan territory, but this one, found near the border of Argentina and Chile, was one of the best preserved, which is why the boy was selected to have his DNA sequenced.
An international team of geneticists led by Antonio Salas from the University of Santiago Compostela in Spain was able to isolate and sequence the boy's entire mitochondrial genome – made up of 37 genes passed down solely by the mother – from just one of his lungs.
His genetic variations place him as part of a population called C1b, a common lineage from Mesoamerica and the Andes that dates back around 18,000 years. There are several known subgroups of the C1b population, but the boy's DNA 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," writes Lizzie Wade for Science.
The team combed genetic databases for any traces of this unique DNA code, but could find only four entries that appeared to belong to C1bi – three modern people from Peru and Bolivia, and one individual from the ancient Wari Empire, which existed in its prime between 600 to 1000 CE.
The fact that two ancient individuals have been identified as part of C1bi made the researchers suggest that the now almost-vanished lineage was once far more common. Especially considering the two ancient samples were picked at random.
"What are the chances that you pick the rare guy?" asked Andrés Moreno-Estrada, a population geneticist from Mexico's National Laboratory of Genomics for Biodiversity who wasn't involved in the study. "Most likely, you’re picking the common guy."
Even if that's the case, the lineage certainly isn't common now and Salas suggests that this might be to do with the Spanish bringing new diseases to South America. “Up to 90 percent of native South Americans died very quickly,” he told Science. “You can imagine that a lot of genetic diversity was lost as well.”
It's hard to say exactly how much we can take from this one case, particularly as only the genes passed down by his mother were sequenced, but it certainly paints an interesting picture about the genetic diversity that once existed in South America.
And for all of you wondering about how the little boy died in this sacrifice ritual, it sadly doesn't seem he had a very peaceful end.
"Vomit stained his clothes red and archaeologists found achiote, a dye which can act as a hallucinogen, in his intestines," writes Alan Yuhas for The Guardian. "He was strangled and died from a blow to the head." :(
The research has been published in Scientific Reports.
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