Friday, December 26, 2014
The fateful triangle
Not long ago Lazaridis et al. proposed that most present-day Europeans were derived from three distinct ancestral populations: Ancient North Eurasians (ANE), Early European Farmers (EEF) and Western European Hunter-Gatherers (WHG).
However, this is essentially a stop-gap model, which will in all likelihood be replaced by a partly revised and more robust model once someone manages to sequence a genome or two from the Neolithic Near East. That's because EEF is clearly a hybrid component, largely made up of ancient Near Eastern ancestry and something very WHG-like, sometimes in very different proportions depending on the location and archeological context of the EEF genomes being analyzed.
So what will this new model look like, you might ask? Probably like this, where EEF is replaced by an Early Neolithic Farmer (ENF) component from the ancient Near East, or something very similar:
The diagram above is basically a Principal Component Analysis (PCA) based on output from my new West Eurasia K8 test (see here), in which the Near Eastern component is synonymous with ENF.
I'm quite certain that these results are very close to the truth. However, just in case the Near Eastern ancestry proportions are a little bit too high (and we won't know until we see those ancient genomes from the Near East), I've got another version that offers lower bound Near Eastern estimates.
It might be useful to keep in mind that I rotated the plots to fit geography. As a result, Component 1, which packs around 85% of the variance on both plots, appears smaller than Component 2, which only carries around 10% of the variance.
A spreadsheet with West Eurasia K8 results for a wide variety of populations is available here. Please note that there are two sheets, with the second sheet showing the lower bound Near Eastern ancestry proportions.
We'll probably learn of more ancient European meta-populations as many more genomes are sequenced from across Eurasia. Nevertheless, I doubt this will affect the model outlined above. That's because I'm expecting all such meta-populations to be mixtures of ANE, ENF and/or WHG, as well as, in some cases, extra-West Eurasian components.
However, I suspect that West Eurasia will have to be modeled in a different way from Europe, with, amongst other things, the so called Basal Eurasian component replacing ENF. But for this to happen we'll need at least one ancient genome that is in large-part of Basal Eurasian origin. In any case, that's a whole different subject.
4mix: four-way mixture modeling in R
ANE is the primary cause of west to east genetic differentiation across West Eurasia
Bell Beaker, Corded Ware, EHG and Yamnaya genomes in the fateful triangle