Wednesday, February 12, 2014

The DNA of the Anzick Baby

Rumors have been flying around North American archaeology for months that study of the bones from the c. 12,800-year-old "Anzick baby" had produced a readable DNA sequence. Now the results have finally been made public:
Sequencing DNA from the 12,600-year-old skeleton of an infant found in central Montana, scientists have confirmed that early Native Americans descended from ancient Asians, not from Western Europeans, according to a study published in Nature today (February 12). This work, led by ancient DNA expert Eske Willerslev of the University of Copenhagen and his colleagues, marked the first ancient North American genome to have been fully sequenced.

The male infant, “Anzick-1,” who was thought to have been between 12 to 18 months old when he died, was excavated in 1968 from a burial site. His skeleton is the oldest known specimen unearthed in North America belonging to the Clovis people, who populated the continent between 13,000 and 12,600 years ago. The boy was buried alongside 125 ancient artifacts including, antler tools. . . .
The results suggest that the Clovis population was genetically "basal" for American Indians, that is, the child was part of a small group of men who fathered all Native Americans other than a few late arrivals.
Anzick-1’s genome also suggests that modern Native Americans are direct descendants of the Clovis population. The ancient genome is similar to those of peoples from both North and South America, suggesting that a single founding population migrated into the Americas close to the time of the last Ice Age.

“So there is a continuity of contemporary Native American populations with this Clovis individual dating back 12,600 years ago,” said Brian Kemp, a molecular anthropologist at the Washington State University, who was not involved in the study.

Comparisons of the ancient boy’s genome with genomic data from native North, Central, and South Americans further revealed that some native North American populations may have diverged early in the history of the first American people. Additional North American genomes will be needed to trace the evolution of the people that gave rise to the modern populations of the Americas.

The researchers also showed that Anzick-1’s maternally inherited mitochondrial DNA is part of the D4a3a haplotype, a founding American lineage that is now only found in about 1.5 percent of modern Native Americans. The rare D4h3a haplotype was also identified in a 10,300-year-old specimen uncovered in Alaska in 2007.
This result is another powerful piece of evidence for the "Clovis first" theory, which holds that most Native Americans descend from the Clovis people, who in turn descend from a single band of Asians who crossed into North America around 13,500 years ago. Yes, there are lots of archaeological sites in North America with radiocarbon dates older than Clovis, and other hints of human presence going back 35,000 years. But if there were such people, they somehow remained quite obscure for thousands of years and then died out, leaving no detectable genetic signature in modern American Indians. All of which is possible under a variety of scenarios, just not very likely.

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