Australasian Science Magazine

The first large-scale study of ancient DNA from early American people has confirmed the devastating impact of European colonisation on the Indigenous American populations of the time.

Published in Science Advances (http://tinyurl.com/za9vzu9), the study reveals a striking absence of pre-Columbian genetic lineages in modern Indigenous Americans, and thus points to the extinction of these lineages with the arrival of the Spaniards.

The research team reconstructed maternal genetic lineages of Indigenous American populations by sequencing mitochondrial genomes extracted from bone and teeth samples taken from 92 pre-Columbian human mummies and skeletons aged between 500 and 8600 years old.

“Surprisingly, none of the genetic lineages we found in almost 100 ancient humans were present, or showed evidence of descendants, in today’s Indigenous populations,” says joint lead author Dr Bastien Llamas of the Australian Centre for Ancient DNA at The University of Adelaide. “This separation appears to have been established as early as 9000 years ago and was completely unexpected, so we examined many demographic scenarios to try and explain the pattern.

“The only scenario that fit our observations was that shortly after the initial colonisation, populations were established that subsequently stayed geographically isolated from one another, and that a major portion of these populations later became extinct following European contact. This closely matches the historical reports of a major demographic collapse immediately after the Spaniards arrived in the late 1400s.”

The ancient genetic signals also provide a more precise timing of the first people entering the Americas via the Bering Land Bridge that connected Asia and the north-western tip of North America during the last Ice Age.

“Our genetic reconstruction confirms that the first Americans entered around 16,000 years ago via the Pacific coast, skirting around the massive ice sheets that blocked an inland corridor route which only opened much later,” says co-author Prof Alan Cooper. “They spread southward remarkably swiftly, reaching southern Chile by 14,600 years ago.”

“Genetic diversity in these early people from Asia was limited by the small founding populations which were isolated on the Beringian land bridge for around 2400 to 9000 years,” explains joint lead author Dr Lars Fehren-Schmitz of the University of California at Santa Cruz. “It was at the peak of the last Ice Age, when cold deserts and ice sheets blocked human movement, and limited resources would have constrained population size. This long isolation of a small group of people brewed the unique genetic diversity observed in the early Americans.”