A detailed genetic analysis has settled the question of how and when the first Americans arrived in the continent.
Scientists have found that Native American populations from Canada to the southern tip of Chile arrived in at least three waves.
Most are descended entirely from a single group of migrants that crossed over through Beringia, a land bridge between Asia and America that existed during the ice ages, more than 15,000 years ago.
“For years it has been contentious whether the settlement of the Americas occurred by means of a single or multiple migrations from Siberia,” says Professor Andres Ruiz-Linares of University College London.
“But our research settles this debate: Native Americans do not stem from a single migration. Our study also begins to cast light on patterns of human dispersal within the Americas.”
The team studied more than 300,000 specific DNA sequence variations, Single Nucleotide Polymorphisms, in 52 Native American and 17 Siberian groups, examining their genetic similarities and differences.
They found that the second and third migrations have left an impact only in Arctic populations that speak Eskimo-Aleut languages, and in the Canadian Chipewyan who speak a Na-Dene language.
However, even these populations have inherited most of their genome from the first migration. Eskimo-Aleut speakers derive more than 50 percent of their DNA from these First Americans, and the Chipewyan around 90 percent.
Once in the Americas, people expanded southward, sticking to the coast with populations splitting off along the way.
“There are at least three deep lineages in Native American populations,” says David Reich, professor of genetics at Harvard Medical School.
“The Asian lineage leading to First Americans is the most anciently diverged, whereas the Asian lineages that contributed some of the DNA to Eskimo-Aleut speakers and the Na-Dene-speaking Chipewyan from Canada are more closely related to present-day East Asian populations.”
One Big Migration Spawned Most–But Not All–Indigenous Americans
By Katherine Harmon | July 11, 2012 | 11
At least 15,000 years ago intrepid Siberians crossed the newly exposed Bering land bridge to arrive in the unpeopled Americas. But was this influx the only ancient wave from East Asia? Researchers have been studying archeological, linguistic and genetic evidence for years in a quest to understand how the first Americans arrived and spread through the continents.
A new large-scale genomic study paints a much clearer picture of these early entrances and distant dispersals that led some people all the way to Tierra del Fuego in a matter of millennia. At least three major waves of migrants from Siberia hit the Americas, but not all of them have had the same reach, according to the findings, which were published online July 11 in Nature (Scientific American is part of Nature Publishing Group).
To arrive at a much-clarified historical portrait, the researchers collected genetic data from 493 people belonging to one of 52 contemporary American Indian groups from Canada to southern South America. They then compared common genetic variances with those of 245 people from 17 current Siberian groups. The key to this study was isolating the genetic variables to those that were specific to American Indian populations, which starting in the 15th century became obscured by genetic “noise” from the substantial amount of European and African influence, the researchers noted.
The initial wave, nicknamed the “First American” group, is the ancestral forebearers of every sampled group from the Yghan in southern Chile to most of Canada’s First Nations groups. But two subsequent groups, “Eskimo-Aleut” and “Chipewyan,” followed, contributing genes only to their respective Artic groups. “The Asian lineage leading to the First Americans is the most anciently diverged,” said David Rich, a geneticist at Harvard Medical School and co-author of the new paper, in a prepared statement. “The Asian lineages that contributed some of the DNA to Eskimo-Aleut speakers and the Na-Dene-speaking Chipewyan from Canada are more closely related to present-day East Asian populations.”
These later groups were apparently quick to mingle with the established populations in northern North America, so much so that Eskimo-Aleut genes sampled retained only about 43 percent of their later wave ancestor’s profiles (the rest being composed of those from the First American group)—and the Chipewyans retained only about 10 percent of their later-wave ancestry (90 percent of the variances studied belonging to the First American profile).
Based on the current analysis, very little genetic remixing appears to have occurred once groups went their separate ways throughout the continents. The exception is one group in Latin America, namely, speakers of the Chibchan languages, who live in Costa Rica, Panama and Colombia. The new genomic research shows that Chibchan speakers today carry both North and South American genetic signatures, suggesting that their ancestors subsequently moved back up the Panama isthmus.
Interestingly, the researchers also found traces of Eskimo-Aleut genetic variants in current-day coastal Siberian populations of the Naukan and Chukchi. So perhaps the Americas weren’t quite to everyone’s liking.
A 1996 study “Mitochondrial DNA Analysis of Mongolian Populations and Implications for the Origin of New World Founders” by Connie J. Kolman et al. concluded that due to the presence of the four New World haplogroups throughout the Americas, “… populations in east Central Asia represent the closest genetic link between the Old World and the New World. All four New World haplogroups have been detected in Mongolian, central Chinese and Tibetan populations that delineate the only region in Asia where all four haplogroups exist and no population lacking any one of the haplogroups occurs.” The findings proposed that “the narrow strip of east Central Asia that extends from Mongolia to the Pacific coast may have served as the starting point for the human migration that led to colonization of the New World”.
The study also found that “Lack of group B haplotypes would appear to eliminate Siberians as possible New World founders despite their geographic proximity to the Americas. In fact, evidence exists that suggests that Siberia may have been colonized subsequent to the New World based on more recent divergence dates for Siberian C and D haplotypes relative to New World C and D haplotypes
(13,500-27,000 YBP us. 18,750-37,500 YBP) (TORRONI et al. 1993b). An additional challenge to Siberian ancestry of New World groups comes from several virology studies that detected human T-cell lymphotrophic retrovirus (HTLV-11) in 11 of 38 Amerind groups tested (e.g., LAIRMORE et al. 1990; MALONEY et al. 1992) and also in Mongolians (HALL et al. 1994) but not in 10 Siberian groups assayed (NEEL et al. 1994).
The fact remains, however, that A, C and D haplotype frequencies are elevated in many Siberian populations relative to other Asian groups (Figure 5) suggesting an
historical relation between Siberians and New World indigenous groups. SZATHMARY (1994) confirmed the close genetic relationship between circumarctic populations in a UPGMA analysis of 15 blood group and allo-
zyme markers that revealed that Siberian, New World Eskimo and Athapaskan (subset of Na-Dene) populations clustered with each other and not with other Asian or Amerind groups. Thus, Siberians and other circumarctic populations may share a similar genetic origin or their close genetic relationship may reflect long-term genetic exchange.”
The study also cited older evidence:
“TURNER (1984) proposed that migration (s) to the New World originated in the area of northern China and southeastern Siberia based on the spread of Sinodontic dental characters throughout northeast Asia and the New World and a notched unifacial spear point (similar to Clovis spear points excavated in the southwestern United States) discovered in Novopetrovka (DEREVLANKO 1969). Phylogenetic analysis of protein polymorphisms in populations distributed throughout the world (29 loci from 26 populations) led NEI and ROYCHOUDHURY (1993) to suggest that migrations out of east Central Asia might have colonized the New World, Japan and the Polynesian and Micronesian Islands. Mitochondrial DNA (mtDNA) studies have identified a COII/tRNALYs 9-bp intergenic deletion that is widespread in New World populations and present in Mongol, Altai and Tibetan populations, but absent in Siberian groups (SAMBUUGHIN et al. 1991; SHIELDS et al. 1992, 1993; TORRONI et al. 1993b, 1994b). Based on the 9-bp deletion and three restriction fragment length polymorphisms (RFLPs), recent molecular genetic studies have identified four mtDNA haplotypes in the New World that are proposed to represent founding lineages (TORRONI et al. 1992) … that can be used as a molecular genetic footprint to search for possible New World ancestors in Asian populations.”