Post by Admin on Jun 7, 2021 22:38:01 GMT
An Australasian Connection
Recently, we carried out a stringent test of the null hypothesis of a single founding population of Central and South Americans using genome-wide data from diverse Native Americans [36]. We detected a statistically clear signal linking Native Americans in the Amazonian region of Brazil to present-day Australo-Melanesians and Andaman Islanders (‘Australasians’). Specifically, we found that Australasians share significantly more genetic variants with some Amazonian populations—including ones speaking Tupi languages—than they do with other Native Americans. We called this putative ancient Native American lineage “Population Y” after Ypykuéra, which means ‘ancestor’ in the Tupi language family.
To learn more about the Population Y ancestry present in the Americas, we carried out a series of statistical modeling analyses. The genetic patterns could be explained by as little as 2% admixture from an Australasian-related population that penetrated deep inside the Americas without mixing with the main ancestral lineage of present-day Native Americans. Alternatively, the patterns could be more explained by a larger proportion of ancestry (2-85%) from a population that existed in a substructured Northeast Asia, and was similar to the main lineage that gave rise to other Native Americans while retaining more Australasian affinity.
Figure 3.
Holocene migrations to the Americas.
There is a current consensus supporting a Paleoeskimo migration to Greenland ~4,500 years ago, giving rise to both the Saqqaq culture and the Early, Middle and Late Dorset cultures. This Paleoeskimo population was displaced by Neo-Eskimos associated with the Thule culture migrating through the Arctic ~1,000 years ago, although there remains a possibility of some admixture. Two scenarios can plausibly explain the Asian ancestry flow in present-day speakers of Athabaskan (Na-Dene) languages. 1) The Na-Dene have ancestry from a distinct migration to the Americas from that seen in any other ancient samples. 2) The Na-Dene-specific ancestry comes from the same migration as the Paleoeskimos [23]. A proposed model in which the Na-Dene-specific ancestry is from the same migration that contributed to the Inuit [34] has been rejected statistically [23].
We considered the possibility that these genetic patterns relate to the claims based on skeletal morphology that there was an wave of migration related to Australasians that contributed to early Native Americans, followed by later large-scale population replacement by the primary ancestors of present-day Native Americans [37,38]. While this evidence has been contested on morphological grounds—with the most important critique being that the analyses are not statistically compelling [2,39]—the fact that the morphological evidence is strongest in Brazil where Population Y ancestry is prevalent justifies investigation into possible connections. However, new genetic findings reject one set of the arguments based on morphology: that groups such as historic-period Native Americans in the Baja California region of Mexico and the Tierra del Fuego region in the southern tip of South America are related to the hypothesized earlier Native American migration. Genomic DNA from these populations do not have any evidence of affinity to Australasian populations [34].
What is the history behind the Population Y ancestry in Amazonian Native Americans today? Little can be said at present, as we do not have ancient DNA from individuals carrying detectable amounts of this ancestry. The implication that the Siberian populations that gave rise to the ancestors of Native Americans was substructured, however, is not surprising given that the 24,000-18,000 years from the Lake Baikal region of Siberia (the Mal’ta and Afontova Gora sites) were genetically very divergent from present-day East Asians [35,40]. The Population Y results suggest that a population that has not yet been sampled with ancient DNA data—one with more Australasian-related ancestry—may also have been present in the broad geographic area to contribute to the founders of Native American founders. Notably, Andaman Islanders, the population with the single strongest affinity to Amazonians, are not as good match for the non-Marta like ancestry in Central Americans as are Chinese populations [36]. These strands of evidence suggest a minimum three-part ancestry of the Beringian populations that came to populate the Americas (Figure 1). Two of these strands were fully braided together to form the main ancestral lineage of Native Americans by time of the Beringian bottleneck. However, the third strand, with an affinity to Australasians, was not.
It has been suggested that Native American ancestors may have entered the more temperate parts of North American both by an early coastal route and the later ice free corridor [2]. One possibility is that the different sources of deep ancestry that are inferred by these genetic patterns may reflect movements of a substructured Beringian population through these different routes. Alternatively, the patterns could reflect pulses of migration from Beringia occurring at different times (e.g. multiple pulses through the ice free corridor). Restricting study to South America, a related question is the history behind the deeply structured population lineages East and West of the Andes in South America that have been documented based on genomic data [23]. Population Y ancestry may be limited entirely to the eastern populations, raising the possibility that this split was extremely ancient.
Recently, we carried out a stringent test of the null hypothesis of a single founding population of Central and South Americans using genome-wide data from diverse Native Americans [36]. We detected a statistically clear signal linking Native Americans in the Amazonian region of Brazil to present-day Australo-Melanesians and Andaman Islanders (‘Australasians’). Specifically, we found that Australasians share significantly more genetic variants with some Amazonian populations—including ones speaking Tupi languages—than they do with other Native Americans. We called this putative ancient Native American lineage “Population Y” after Ypykuéra, which means ‘ancestor’ in the Tupi language family.
To learn more about the Population Y ancestry present in the Americas, we carried out a series of statistical modeling analyses. The genetic patterns could be explained by as little as 2% admixture from an Australasian-related population that penetrated deep inside the Americas without mixing with the main ancestral lineage of present-day Native Americans. Alternatively, the patterns could be more explained by a larger proportion of ancestry (2-85%) from a population that existed in a substructured Northeast Asia, and was similar to the main lineage that gave rise to other Native Americans while retaining more Australasian affinity.
Figure 3.
Holocene migrations to the Americas.
There is a current consensus supporting a Paleoeskimo migration to Greenland ~4,500 years ago, giving rise to both the Saqqaq culture and the Early, Middle and Late Dorset cultures. This Paleoeskimo population was displaced by Neo-Eskimos associated with the Thule culture migrating through the Arctic ~1,000 years ago, although there remains a possibility of some admixture. Two scenarios can plausibly explain the Asian ancestry flow in present-day speakers of Athabaskan (Na-Dene) languages. 1) The Na-Dene have ancestry from a distinct migration to the Americas from that seen in any other ancient samples. 2) The Na-Dene-specific ancestry comes from the same migration as the Paleoeskimos [23]. A proposed model in which the Na-Dene-specific ancestry is from the same migration that contributed to the Inuit [34] has been rejected statistically [23].
We considered the possibility that these genetic patterns relate to the claims based on skeletal morphology that there was an wave of migration related to Australasians that contributed to early Native Americans, followed by later large-scale population replacement by the primary ancestors of present-day Native Americans [37,38]. While this evidence has been contested on morphological grounds—with the most important critique being that the analyses are not statistically compelling [2,39]—the fact that the morphological evidence is strongest in Brazil where Population Y ancestry is prevalent justifies investigation into possible connections. However, new genetic findings reject one set of the arguments based on morphology: that groups such as historic-period Native Americans in the Baja California region of Mexico and the Tierra del Fuego region in the southern tip of South America are related to the hypothesized earlier Native American migration. Genomic DNA from these populations do not have any evidence of affinity to Australasian populations [34].
What is the history behind the Population Y ancestry in Amazonian Native Americans today? Little can be said at present, as we do not have ancient DNA from individuals carrying detectable amounts of this ancestry. The implication that the Siberian populations that gave rise to the ancestors of Native Americans was substructured, however, is not surprising given that the 24,000-18,000 years from the Lake Baikal region of Siberia (the Mal’ta and Afontova Gora sites) were genetically very divergent from present-day East Asians [35,40]. The Population Y results suggest that a population that has not yet been sampled with ancient DNA data—one with more Australasian-related ancestry—may also have been present in the broad geographic area to contribute to the founders of Native American founders. Notably, Andaman Islanders, the population with the single strongest affinity to Amazonians, are not as good match for the non-Marta like ancestry in Central Americans as are Chinese populations [36]. These strands of evidence suggest a minimum three-part ancestry of the Beringian populations that came to populate the Americas (Figure 1). Two of these strands were fully braided together to form the main ancestral lineage of Native Americans by time of the Beringian bottleneck. However, the third strand, with an affinity to Australasians, was not.
It has been suggested that Native American ancestors may have entered the more temperate parts of North American both by an early coastal route and the later ice free corridor [2]. One possibility is that the different sources of deep ancestry that are inferred by these genetic patterns may reflect movements of a substructured Beringian population through these different routes. Alternatively, the patterns could reflect pulses of migration from Beringia occurring at different times (e.g. multiple pulses through the ice free corridor). Restricting study to South America, a related question is the history behind the deeply structured population lineages East and West of the Andes in South America that have been documented based on genomic data [23]. Population Y ancestry may be limited entirely to the eastern populations, raising the possibility that this split was extremely ancient.