A new press release is circulating on the paper which I blogged a few months ago, Ancient Admixture in Human History. Unlike the paper, the title of the press release is misleading, and unfortunately I notice that people are circulating it, and probably misunderstanding what is going on. Here’s the title and first paragraph:
Native Americans and Northern Europeans More Closely Related Than Previously Thought
Released: 11/30/2012 2:00 PM EST
Source: Genetics Society of America
Newswise — BETHESDA, MD – November 30, 2012 — Using genetic analyses, scientists have discovered that Northern European populations—including British, Scandinavians, French, and some Eastern Europeans—descend from a mixture of two very different ancestral populations, and one of these populations is related to Native Americans. This discovery helps fill gaps in scientific understanding of both Native American and Northern European ancestry, while providing an explanation for some genetic similarities among what would otherwise seem to be very divergent groups. This research was published in the November 2012 issue of the Genetics Society of America’s journal GENETICS
The reality is ta Native Americans and Northern Europeans are not more “closely related” genetically than they were before this paper. There has been no great change to standard genetic distance measures or phylogeographic understanding of human genetic variation. A measure of relatedness is to a great extent a summary of historical and genealogical processes, and as such it collapses a great deal of disparate elements together into one description. What the paper in Genetics outlined was the excavation of specific historically contingent processes which result in the summaries of relatedness which we are presented with, whether they be principal component analysis, Fst, or model-based clustering.
What I’m getting at can be easily illustrated by a concrete example. To the left is a 23andMe chromosome 1 “ancestry painting” of two individuals. On the left is me, and the right is a friend. The orange represents “Asian ancestry,” and the blue represents “European” ancestry. We are both ~50% of both ancestral components. This is a correct summary of our ancestry, as far as it goes. But you need some more information. My friend has a Chinese father and a European mother. In contrast, I am South Asian, and the end product of an ancient admixture event. You can’t tell that from a simple recitation of ancestral quanta. But it is clear when you look at the distribution of ancestry on the chromosomes. My components have been mixed and matched by recombination, because there have been many generations between the original admixture and myself. In contrast, my friend has not had any recombination events between his ancestral components, because he is the first generation of that combination.
So what the paper publicized in the press release does is present methods to reconstruct exactly how patterns of relatedness came to be, rather than reiterating well understood patterns of relatedness. With the rise of whole-genome sequencing and more powerful computational resources to reconstruct genealogies we’ll be seeing much more of this to come in the future, so it is important that people are not misled as to the details of the implications.
By now you have read that the Clovis people may have had contemporaries. In case you didn’t know, until about ~10 years the “standard model” of the peopling of the Americas was that around ~13,000 years ago one single population crossed into the New World via Beringia, and rapidly swept north to south in ~1,000 years. These were the Clovis people, associated with a particular toolkit, and perhaps implicated in megafaunal extinctions. Today this model is no longer held to be sacrosanct, though no clear successor has emerged. It does seem likely that some sort of pre-Clovis population is presumed to exist. These data are interesting because they indicate that there may have been geographical structure in cultural forms even at this early stage in North America, implying that the original peopling of America was not homogeneous. That is, there may have been several founding groups.
I find this entirely plausible. It strikes me that a fear years ago a tendency toward rhetorical extremism occasionally found purchase when it came to the settlement of the peripheries of the human range, Oceania and the New World. Jared Diamond famously proposed that Australia and Papua may have been colonized by one pregnant woman! (presumably she then reproduced with her own son, as Gaia did with Uranus) In hindsight it seems more likely that migration of pre-modern humans was a far more organized affair, and not an ad hoc expansion in a state of anarchy, with family groups splitting off in a random fashion due to demographic pressures. Note that archaic humans did not settle Oceania and the New World, despite having a million years to do so.
Many researchers suppose that the ancestors of the First Americans sojourned in Berengia before they crossed over into the New World (their progress being blocked by glaciers). This may explain why genetic estimates of the populations’ origin tend to be deeper than the archaeological conclusions, even if you push the dates back due to Monte Verde. From the media reports archaeologists seem to be emphasizing that the original population which settled the New World may have been culturally diverse, even if they are genetically similar. Presumably this is a counterpoint to the paper which posits a “First American” group at the heart of the genomic variation of the New World groups.
That is the question, and tentatively answered in the affirmative according to a new paper in The American Journal of Physical Anthropology. A new subclade of mtDNA haplogroup C1 found in icelanders: Evidence of pre-columbian contact?:
Although most mtDNA lineages observed in contemporary Icelanders can be traced to neighboring populations in the British Isles and Scandinavia, one may have a more distant origin. This lineage belongs to haplogroup C1, one of a handful that was involved in the settlement of the Americas around 14,000 years ago. Contrary to an initial assumption that this lineage was a recent arrival, preliminary genealogical analyses revealed that the C1 lineage was present in the Icelandic mtDNA pool at least 300 years ago. This raised the intriguing possibility that the Icelandic C1 lineage could be traced to Viking voyages to the Americas that commenced in the 10th century. In an attempt to shed further light on the entry date of the C1 lineage into the Icelandic mtDNA pool and its geographical origin, we used the deCODE Genetics genealogical database to identify additional matrilineal ancestors that carry the C1 lineage and then sequenced the complete mtDNA genome of 11 contemporary C1 carriers from four different matrilines. Our results indicate a latest possible arrival date in Iceland of just prior to 1700 and a likely arrival date centuries earlier. Most surprisingly, we demonstrate that the Icelandic C1 lineage does not belong to any of the four known Native American (C1b, C1c, and C1d) or Asian (C1a) subclades of haplogroup C1. Rather, it is presently the only known member of a new subclade, C1e. While a Native American origin seems most likely for C1e, an Asian or European origin cannot be ruled out.
The core of the article treads the confusing gray zone between rock-hard precise science and the more vague and intuitive truths of history. One the rock-hard part, there is a huge literature on maternal genetic lineages, the mtDNA. Because this genetic material is copious it was some of the first to be analyzed using molecular clock models. A molecular clock is a feasible with mtDNA because it is haploid; it is only inherited through females and so is not subject to recombination which might break apart associations of distinctive genetic markers. Instead of being a reticulated mesh the genealogy of mtDNA is a clean and inverted elegant tree leading back to a common ancestress. You are finding the line of your mother’s mother’s mother’s mother’s….