The far northeast of Siberia was the gateway to the Americas for ancient humans, and today is home to diverse cultures whose members speak many languages. During the Late Pleistocene period (the ice age that lasted from about 126,000 to 11,700 years ago), this area of Siberia was connected to North America; the land bridge and adjacent areas formed a region known as Beringia. Hunter-gatherer populations seem to have ranged widely1–3 across Siberia and into Beringia, sustained by megafauna such as woolly mammoths, and other animals. Writing in Nature, Sikora et al.4 and Flegontov et al.5 examine the genetic footprints of past peoples in northeastern Siberia and northern North America, to work out their relationships to modern communities. Sikora and colleagues also examine how these peoples were affected by climate change over the past 40,000 years.
Sikora et al. analysed genomic data from 34 people from ancient northeastern Siberia. Two individuals were buried at Yana RHS in Russia — a 31,600-year-old archaeological site that contains the earliest human remains found in the far northeast of Siberia — and the others date from 9,800 to 600 years ago. The Yana individuals provide the only genomic data gathered so far from northeastern Siberia before the Last Glacial Maximum (LGM, about 26,500 to 19,000 years ago), although there is evidence of human occupation in central Siberia as early as 45,000 years ago6.
The limited availability of genomic data from pre-LGM Eurasians has made it challenging for researchers to understand the landscape of human variation at the time. Sikora and colleagues’ analyses support the idea that these populations were wide-ranging, yet structured (there were genetic differences between groups). The authors also suggest that the Yana represent a group that the team calls Ancient North Siberians (ANS), who diverged from Western Eurasians about 38,000 years ago, soon after the latter group split from East Asians.
The land bridge between Eurasia and North America existed from about 34,000 to 11,000 years ago3,7, and it is thought that people migrated onto this bridge sometime between 30,000 and 15,000 years ago. Using palaeoclimate simulations and genetic data, Sikora et al. suggest that at least some ANS moved to southern Beringia during the LGM (Fig. 1), and that these individuals are ancestral both to the first people who inhabited the Americas (sometimes referred to as the First Peoples) and to another group that emerged at about the same time, whom the authors call Ancient Palaeo-Siberians. East Asians contributed 75% of their DNA to the Ancient Palaeo-Siberians, and 63% to the First Peoples, which suggests that there was some geographical separation between the latter two groups. The authors argue that these groups diverged about 24,000 years ago.
After the LGM, major environmental and cultural changes occurred on both sides of the land bridge (as they did elsewhere). In Siberia, archaeological evidence shows that a change in tool technologies occurred, coinciding with a scarcity of mammoth ivory8. This evidence, together with Sikora and colleagues’ genetic data, indicates that population and cultural changes occurred as a result of the expansion of the Ancient Palaeo-Siberian population. The Ancient Palaeo-Siberians were then replaced by, or admixed (produced offspring) with, a group called the Neo-Siberians, between 11,000 and 4,000 years ago.
Also just after the LGM, the First Peoples began their movement southwards9,10. Other groups remained in the north, and it is their subsequent history that is the focus of Flegontov and co-workers’ study. More specifically, the authors examine the relationships between people from several archaeologically defined cultures, including the Palaeo-Eskimos, who spread across the American Arctic from about 5,000 years ago, and the Neo-Eskimos, whose population expanded and might have replaced the Palaeo-Eskimos from about 800 years ago (Fig. 2). The researchers also study how these ancient peoples are related to modern populations who speak Eskimo-Aleut, Na-Dene and other languages.
Flegontov et al. examined about 1.24 million variable nucleotide sites across the genome from 48 ancient individuals and from modern Iñupiat, who live in northern Alaska. Previous research11 has led to debate about whether the Palaeo-Eskimo admixed with other groups. Flegontov and colleagues’ data demonstrate that the Palaeo-Eskimo lineage did indeed contribute to the Neo-Eskimo group, and thus its members are among the ancestors of modern Eskimo-Aleut speakers, as well as of Na-Dene-speaking peoples.
Both of the new papers present analyses and discussions of the Palaeo-Eskimo peoples: Sikora et al. focus on their Siberian ancestors, whereas Flegontov et al. examine their relationship to subsequent populations in North America. Sikora et al. identify Palaeo-Eskimo individuals (including a Saqqaq individual, who lived in Greenland) as being admixtures of the Ancient Palaeo-Siberian and East Asian lineages; Flegontov et al. call this Siberian ancestry the Proto-Palaeo-Eskimo lineage. Both papers also describe evidence of ancient people interacting across the Bering Strait, and of migration back to Siberia. Sikora et al. suggest that Ancient Palaeo-Siberians contributed DNA to modern Na-Dene speakers, but (unlike Flegontov et al.) propose that this came from Siberian ancestors, rather than from Palaeo-Eskimos.
One limitation of the two papers is that, although some of the DNA samples analysed by the two research groups came from the same archaeological sites, it is difficult to tell whether the same individuals were sampled — a problem that can arise in studies of archaeological material. A general code of practice would be useful for this field, to encourage scientists to provide the identifiers used by the original excavators, thus enabling cross-study comparisons and validations. This would help to ensure that the destructive sampling of archaeological remains, which are non-renewable resources, is properly coordinated and minimized. The code of practice could also ensure that descendants of ancient individuals are engaged in discussions about sampling (as exemplified by Flegontov et al., who note that they consulted Alaskan communities in their study).
Both studies reveal not only the complexity of the interactions that occurred within and between Siberian and northern North American populations over time, but also the impact of climate change — specifically, how the ice-age climate drove people to ‘refugia’ (locations where humans could survive) during the LGM, and subsequent population expansions into other regions when the ice receded or the climate improved. However, we have no human genetic data from the roughly 20,000-year period after the initial occupation of the Yana site. This is a huge gap, in archaeological terms. Further studies of Siberian and Beringian populations during this period are now needed to learn more about the genetic and cultural diversity of these groups.
More work is also needed to understand where the refugia were in northeastern Siberia, and what environmental conditions were like in these regions. In particular, what was the population structure in the Beringian refugium, and does this support the Beringian standstill hypothesis — which posits that the First Peoples became isolated during the LGM, before the southward expansion of the ice sheets12?
In the ongoing debate about how many ‘waves’ of migration led to the establishment of human populations in the Americas, the new papers could be interpreted as suggesting that there were just two: the First Peoples and the Palaeo-Eskimo peoples. If so, then how does this tally with the idea that some Amazonian populations seem to share DNA13,14 with people who speak Austronesian languages (who live today in southeast Asia, Oceania and Madagascar)? Did the populations in the Beringian refugium also have this ancestry? Lastly, how did environmental changes, human migrations and cultural and genetic adaptations interplay in northeastern Siberia and the far northern Americas? The two latest studies will help us to get our bearings as we work to understand the ancient humans who lived around the Bering Strait.
Nature 570, 170-172 (2019)