A paper in Nature this week presents analysis of the ancient genome of an infant skeleton from Alaska, some 11,500 years old: “Terminal Pleistocene Alaskan genome reveals first founding population of Native Americans”.
Jennifer Raff has done a very nice write-up for the Guardian of the implications of these new data for models of the initial habitation of the Americas: “What the ancient DNA discovery tells us about Native American ancestry”. Of particular interest is the way that this genome helps to resolve the approximate ages of population divergences as people entered Beringia and later the southern parts of the Americas.
She did not belong to either of the two major Native American genetic groups (Southern and Northern), but was equally related to both of them. One interpretation of this result is that her ancestors must have remained in Alaska after splitting from the ancestors of Native Americans sometime around 20,000 YBP. Her genome, provides new insight into the genetic diversity present in the ancestral Beringian population. One important component of that is that it gives us new estimates of the approximate dates of key events:
36,000 YBP: The ancestors of the ancient Beringians began to separate from East Asians, but gene flow between them continues until about 25,000 YBP
25-20,000 YBP: This population experienced gene flow with the ancient North Eurasian population (to which the Mal’ta boy belonged)
20,000 YBP: The ancestors of the Upward Sun River child diverged from the ancestors of other Native Americans.
17,000-14,600 YBP: The two major clades (genetic groups) of Native Americans differentiate from one another.
While this paper doesn’t yield any tremendous surprises, it does add new details to and confirms the predictions of a hypothesis for the initial peopling of the Americas that has been the focus of much research over the past few years.
I may have more to say about this later. It is of interest that this genome, like other Paleoamerican genomes so far, lacks the evidence of a slight fraction of South or Southeast Asian ancestry that some researchers have claimed to be present in some living populations from South America.