February 21, 2018

Caribbean Taino ancient DNA still alive in admixed populations

Taino Native Americans also had a very high genetic diversity, comparable to other continental large native populations such as Andeans or Amazonians, what speaks of high mobility in the Caribbean islands before European colonization.

The mitochondrial lineage B2 was sequenced, although it is today rare in the region.

Hannes Schroeder et al., Origins and genetic legacies of the Caribbean Taino. PNAS 2018. DOI:10.1073/pnas.1716839115

The Caribbean was one of the last parts of the Americas to be settled by humans, but how and when the islands were first occupied remains a matter of debate. Ancient DNA can help answering these questions, but the work has been hampered by poor DNA preservation. We report the genome sequence of a 1,000-year-old Lucayan Taino individual recovered from the site of Preacher’s Cave in the Bahamas. We sequenced her genome to 12.4-fold coverage and show that she is genetically most closely related to present-day Arawakan speakers from northern South America, suggesting that the ancestors of the Lucayans originated there. Further, we find no evidence for recent inbreeding or isolation in the ancient genome, suggesting that the Lucayans had a relatively large effective population size. Finally, we show that the native American components in some present-day Caribbean genomes are closely related to the ancient Taino, demonstrating an element of continuity between precontact populations and present-day Latino populations in the Caribbean.

Fig. 2.
Taino demography. Total estimated length of genomic ROH for the Taino and the Clovis genome (13) and selected Native American and Siberian genomes (15, 31, 32) in a series of length categories. ROH distributions for modern individuals have been condensed into population-level silhouettes (SI Appendix, section 14).

February 17, 2018

Ironworks the Iron Age style: the true thing done again by Burkinabe elders for the sake of historical document

This is a truly fascinating film, made by the people of Burkina Faso documenting their own, now vanishing tradition of iron smelting and forging, done again for the sake of historical documentation by the elders who used to do it decades ago (and some youngsters helping too) reproducing all the steps: from charcoal making and iron ore mining and selection, to the construction of the furnaces, the smelting of ore and finally tool-making itself. I cannot recommend it more wholeheartedly:

Obsidian exchange in Neolithic Sicily and Sardinia (video)

Thanks to Theasparagus for noticing this quite interesting video-lesson on quite obviously seagoing peoples of the Central Mediterranean and their journeys to distant volcanic islands to obtain the valuable obsidian (sharper than a scalpel) and also to the mainland to trade it for whatever goods.

February 14, 2018

Dystruct versus Admixture

Not really able yet to discern if this is an alternative way ahead for autosomal archaeogenetics or just another dead end. But it does seem interesting enough to mention here in any case.

It may be very important in the deciphering of the so-called "ANE" ghostly genetic influence.

Tyler A. Joseph & Itsik Pe'er. Inference of population structure from ancient DNA. bioRXiv 2018 (pre-pub). DOI:10.1101/261131

Methods for inferring population structure from genetic information traditionally assume samples are contemporary. Yet, the increasing availability of ancient DNA sequences begs revision of this paradigm. We present Dystruct (Dynamic Structure), a framework and toolbox for inference of shared ancestry from data that include ancient DNA. By explicitly modeling population history and genetic drift as a time-series, Dystruct more accurately and realistically discovers shared ancestry from ancient and contemporary samples. Formally, we use a normal approximation of drift, which allows a novel, efficient algorithm for optimizing model parameters using stochastic variational inference. We show that Dystruct outperforms the state of the art when individuals are sampled over time, as is common in ancient DNA datasets. We further demonstrate the utility of our method on a dataset of 92 ancient samples alongside 1941 modern ones genotyped at 222755 loci. Our model tends to present modern samples as the mixtures of ancestral populations they really are, rather than the artifactual converse of presenting ancestral samples as mixtures of contemporary groups.

Still digesting this one but I do find very intriguing that they claim that Dystruct has much less time-entropy than ADMIXTURE (i.e. the relation between ancient and modern populations seems to be better identified) and that, using this method they get that the Samara (proto-Indoeuropean) population becomes much more clearly related to Kostenki-14 (a Gravettian hunter-gatherer from the Don area) and that the Paleo-Siberian "ANE" individuals form then their own distinct cluster with very limited impact in Europe (but much larger in parts of Asia (not labeled: South Asia?). This Kostenki-Samara "orange" component keeps influencing Western Indoeuropeans (Corded Ware, Unetice) but at markedly decreasing frequencies of "purity". 

However the first admixture of Corded Ware is not with earlier farmers (mostly "green") but with some sort of late "hunter-gatherer" population ("brown" or "maroon" component. Only after the backlash of Bell Beaker, which in Central Europe appears as a mix of Neolithic peoples, Indoeuropeans and maybe even more of that mysterious extra HG element, we see some "return of the farmers", which clearly persists in Unetice.

In general, modern Europeans are (fig.5a, not shown here) quite "greener" than Unetice and some populations (I'm guessing Sardinians and Basques, no labels provided) have zero "orange" (IE) component, which ranges (my visual estimate) between 9% and  27% otherwise.

Fig.5-b (click to expand): Ancestry estimates for 92 ancient samples. The three leftmost samples are the Pleistocene hunter-gatherers. In Dystruct, late Neolithic samples and beyond present as a mixture of hunter-gatherers, Yamnaya steppe herders,and early Neolithic samples, matching supported historical migrations of steppe herders into Eastern and Western Europe.

February 13, 2018

Scandinavian hunter-gatherers had double west-east origins

SHG origins' mystery solved? What about possible Norwegian "EHG-like" genetic influences into Atlantic Europe?

Torsten Günther, Helena Malmström, Emma Svensson, Ayça Omrak et al. Genomics of Mesolithic Scandinavia reveal colonization routes and high-latitude adaptation. bioRXiv 2017 (pre-pub). DOI:10.1101/164400

Scandinavia was one of the last geographic areas in Europe to become habitable for humans after the last glaciation. However, the origin(s) of the first colonizers and their migration routes remain unclear. We sequenced the genomes, up to 57x coverage, of seven hunter-gatherers excavated across Scandinavia and dated to 9,500-6,000 years before present. Surprisingly, among the Scandinavian Mesolithic individuals, the genetic data display an east-west genetic gradient that opposes the pattern seen in other parts of Mesolithic Europe. This result suggests that Scandinavia was initially colonized following two different routes: one from the south, the other from the northeast. The latter followed the ice-free Norwegian north Atlantic coast, along which novel and advanced pressure-blade stone-tool techniques may have spread. These two groups met and mixed in Scandinavia, creating a genetically diverse population, which shows patterns of genetic adaptation to high latitude environments. These adaptations include high frequencies of low pigmentation variants and a gene-region associated with physical performance, which shows strong continuity into modern-day northern Europeans.

Fig. 1:
Mesolithic samples and their genetic affinities – (A) Map of the Mesolithic European samples used in this study. The pie charts show the model-based [16,17] estimates of genetic ancestry for each SHG individual. The map also displays the ice sheet covering Scandinavia 10,000 BP (most credible (solid line) and maximum extend (dashed line) following [10]). Newly sequenced sites are shown in bold and italics, SF11 is excluded from this map due to its low coverage (0.1x). Additional European EHG and WHG individuals used in this study derive from sites outside this map (...)

Intriguingly, Swedish Epipaleolithic peoples (SHG) have the light skin variant in the gene SLC45A2, variant that is now uniformly spread through all Europe and accounts for 15% of the skin color variance in a key Cape Verde study and that was so far attributed solely (or almost solely) to Neolithic farmers (among which it was fixated and who had indeed a very large genetic impact in the European subcontinent). They also have the blue eyes allele, as Western Hunter-Gatherers did. However, if we are to follow, Günther's explanations in this video, the variance of looks in Epipaleolithic Scandinavia was greater than in present day. 


PS- Legend says that when my namesake Fray Luis de León returned to his classroom after five years imprisoned by the Inquisition, he began his class with these words: "As we were saying yesterday..."

Expect less lengthy articles because I really want to use this blog as open notebook, and not spend so much time following news and dissecting them thoroughly, so my style may become a bit more telegraphic. 

I also don't know for how long I will be able to continue blogging, as my personal economic situation is bad and worsening and you never know when police may come and arrest you for saying "fuck the king" or whatever other quite reasonable opinion. We live very troubled times and I'm personally quite bad at winning.

Also my apologies in advance if I fail to quickly approve comments. I usually check my email once per day or so but sometimes I just forget. Please, be patient if that happens: I only censor fascism, racism, sexism and homophobia (and those individuals who have managed to really get on my nerves, and they know who they are). Sadly I have to keep pre-moderating all comments, else the lonely troll will get away with his abuses.