The American Journal of Physical Anthropology (AJPA) recently published an article by Ebenesersdottier et al. dealing with a newly discovered mitochondrial DNA (mtDNA) lineage: A New Subclade of mtDNA Haplogroup C1 Found in Icelanders: Evidence of Pre-Columbian Contact? This paper is particularly interesting to me as I recently published an article in Genome Research about another C1 lineage. In fact, prior to the new study in AJPA, the known mtDNA C1 lineages were: C1a, found at very low frequencies in Asia, and C1b, C1c, and C1d (the latter being the subject of my recent publication) who are autochthonous to the Americas. As a reminder, mtDNA is inherited exclusively along the maternal line and therefore it offers a female perspective about human evolution, expansions and migrations from a female viewpoint (Achilli and Perego, 2010). Tamm et al. 2007 was the first study proposing the origin and dispersion of these four C1 lineages (see figure below). In that work, the authors proposed a differentiation of the C1 subclades in Beringia during the Last Glacial Maximum, approximately 20,000 years ago. This time also corresponds to the mtDNA mutation estimate for C1 as a whole. Tamm et al. suggested that after differentiating -- and following the improvement of climate conditions -- C1a returned to Asia, while C1b, C1c, and C1d found their way into the pristine American double-continent. These three lineages are found at different frequencies in tribal groups of North, Central and South America, thus being true pan-American haplogroups. C1d is the rarer of the three and the reason I decided to study it in greater details in my last publication.
Now, a fifth C1 lineage has been reported in Iceland. How does it fit with the rest of the mtDNA C1 picture? Genealogical and phylogenetic analyses of the Icelandic C1 haplotype (called C1e) revealed that its presence in Iceland is indeed quite ancient, and not the result of recent admixture, as it was initially postulated. The Icelandic C1e is characterized by a set of 11 control and coding region mutations that distinguish it from its four sister clades. A survey of worldwide mtDNA samples (both complete sequences and control region haplotypes in modern and ancient mtDNAs) identified a single sample sharing C1e characteristics in a German individual. Because of its rarity in Western Eurasia, the authors excluded the Old World as the cradle for the novel Icelandic mtDNA. However, there is enough evidence to conclude that such lineage has been present in the Icelandic mtDNA pool prior to the arrival of Christopher Columbus to the Americas, thus raising the question about a possible pre-1492 contact between Icelanders and American's natives. The highly disputed and controversial Solutrean Hypothesis, which proposes a genetic and cultural contribution from the Old to the New World across the ice-cap that once connected the two landmasses in the Northern Hemisphere could be resurrected after the discovery of this new mtDNA lineage. However, the authors feel more comfortable with the possibility of Viking voyages between Iceland and northern North America that resulted in the migration of at least one Native American woman (carrying the C1 lineage) back to the Old World. Since no C1e lineage has been detected in modern American indigenous populations, the authors emphasized that "given the rather drastic population size reductions that resulted from the actions of Europeans after 1492, it is quite possible that the C1e lineage was once carried by, but has now been lost from contemporary individuals with Native American matrilineal ancestry."
Such discovery has a number of implications in the ongoing debate of DNA vs. Book of Mormon:
1. We are reminded once more that we are dealing with related sister clades, but we still don't know much about their ancestral nodes. In other words, we know that C1a is found exclusively in Asia, that C1b, C1c, and C1d are indigenous mtDNA lineages of the Americas, and now we know that C1e is found in the Old World. However, no traces of the ancestral C1 haplogroup in modern populations has been found, thus leaving us with an estimate age for its existence (approximately 20,000 years ago, Perego et al. 2009), but not an exact geographic location for its origin. The common ancestor for all the C1 lineages was not necessarily at the branch point of the migration -- e.g. if the founders of two populations originally co-existed in the same region (and shared a common ancestor thousands of years prior) and then both migrated somewhere else and founded a population in their new regions, it can't necessarily be assumed that they lived in the same place, but only how far back that common ancestor lived. If Beringia once housed C1 mtDNA lineages, then the only explanation is that C1e was one of the Beringian clades, which then migrated to Iceland before disappearing in the American continent. Possible, but a bit of a stretch. It definitely leaves rooms for additional explanations.
2. As of today, no evidence of C1e in the modern American population has been found. This would be further confirmation that certain mtDNA lineages could have been part of the historical genetic pool of Native Americans, but that it has disappeared in our days. If C1e was in the Americas and then it disappeared, couldn't the same thing have happened to other maternal lineages as well?
3. If C1e is instead an Old World mtDNA lineage (a sister clade distantly related to the Asian-American ones), then a similar argument could be proposed for haplogroup X2a, which is also found exclusively in the Americas and it is quite different from its Old World counterparts. In other words, all these lineages share a common ancestor, but we are unsure about when and especially where these female progenitors once lived (including how the lineages expanded from the original geographic region to their current locations). Tamm et al. 2007 figure (below) would need to be updated to include possible migratory and expansion routes that would include the newly discovered C1e lineage.
In conclusion, it appears that as new mtDNA lineages with Native American affinity are identified and made available through scholarly publications, the question surrounding the peopling of the Americas and the contacts these Natives may have had through the millennia with Old World migrants is far from being completely resolved. As the authors of the current study put it, "although the complete sequence of the Icelandic C1 lineage fully resolved its position in the human mtDNA tree, the mystery surrounding the lineage's geographical origin has only deepened." This is basically the case for all Native American mtDNA clades.
Now, a fifth C1 lineage has been reported in Iceland. How does it fit with the rest of the mtDNA C1 picture? Genealogical and phylogenetic analyses of the Icelandic C1 haplotype (called C1e) revealed that its presence in Iceland is indeed quite ancient, and not the result of recent admixture, as it was initially postulated. The Icelandic C1e is characterized by a set of 11 control and coding region mutations that distinguish it from its four sister clades. A survey of worldwide mtDNA samples (both complete sequences and control region haplotypes in modern and ancient mtDNAs) identified a single sample sharing C1e characteristics in a German individual. Because of its rarity in Western Eurasia, the authors excluded the Old World as the cradle for the novel Icelandic mtDNA. However, there is enough evidence to conclude that such lineage has been present in the Icelandic mtDNA pool prior to the arrival of Christopher Columbus to the Americas, thus raising the question about a possible pre-1492 contact between Icelanders and American's natives. The highly disputed and controversial Solutrean Hypothesis, which proposes a genetic and cultural contribution from the Old to the New World across the ice-cap that once connected the two landmasses in the Northern Hemisphere could be resurrected after the discovery of this new mtDNA lineage. However, the authors feel more comfortable with the possibility of Viking voyages between Iceland and northern North America that resulted in the migration of at least one Native American woman (carrying the C1 lineage) back to the Old World. Since no C1e lineage has been detected in modern American indigenous populations, the authors emphasized that "given the rather drastic population size reductions that resulted from the actions of Europeans after 1492, it is quite possible that the C1e lineage was once carried by, but has now been lost from contemporary individuals with Native American matrilineal ancestry."
Such discovery has a number of implications in the ongoing debate of DNA vs. Book of Mormon:
1. We are reminded once more that we are dealing with related sister clades, but we still don't know much about their ancestral nodes. In other words, we know that C1a is found exclusively in Asia, that C1b, C1c, and C1d are indigenous mtDNA lineages of the Americas, and now we know that C1e is found in the Old World. However, no traces of the ancestral C1 haplogroup in modern populations has been found, thus leaving us with an estimate age for its existence (approximately 20,000 years ago, Perego et al. 2009), but not an exact geographic location for its origin. The common ancestor for all the C1 lineages was not necessarily at the branch point of the migration -- e.g. if the founders of two populations originally co-existed in the same region (and shared a common ancestor thousands of years prior) and then both migrated somewhere else and founded a population in their new regions, it can't necessarily be assumed that they lived in the same place, but only how far back that common ancestor lived. If Beringia once housed C1 mtDNA lineages, then the only explanation is that C1e was one of the Beringian clades, which then migrated to Iceland before disappearing in the American continent. Possible, but a bit of a stretch. It definitely leaves rooms for additional explanations.
2. As of today, no evidence of C1e in the modern American population has been found. This would be further confirmation that certain mtDNA lineages could have been part of the historical genetic pool of Native Americans, but that it has disappeared in our days. If C1e was in the Americas and then it disappeared, couldn't the same thing have happened to other maternal lineages as well?
3. If C1e is instead an Old World mtDNA lineage (a sister clade distantly related to the Asian-American ones), then a similar argument could be proposed for haplogroup X2a, which is also found exclusively in the Americas and it is quite different from its Old World counterparts. In other words, all these lineages share a common ancestor, but we are unsure about when and especially where these female progenitors once lived (including how the lineages expanded from the original geographic region to their current locations). Tamm et al. 2007 figure (below) would need to be updated to include possible migratory and expansion routes that would include the newly discovered C1e lineage.
In conclusion, it appears that as new mtDNA lineages with Native American affinity are identified and made available through scholarly publications, the question surrounding the peopling of the Americas and the contacts these Natives may have had through the millennia with Old World migrants is far from being completely resolved. As the authors of the current study put it, "although the complete sequence of the Icelandic C1 lineage fully resolved its position in the human mtDNA tree, the mystery surrounding the lineage's geographical origin has only deepened." This is basically the case for all Native American mtDNA clades.
Above: Figure 2 from Tamm et al. 2007 indicating the migration directions for C1a, C1b, C1c, and C1d from their refugium in Beringia. Below: Figure 5 from Ebensersdottir et al. 2010 indicating the phylogeny of all known complete mtDNA sequences belonging to C1.
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