Genomic history of Eurasia

The route of modern humans out of Africa has been contentious, with archaeological and genetic finds pointing towards a route through Egypt, versus one through Ethiopia. Pagani et al. (2015) analyze the genomic admixture of individuals sampled from both Egypt and Ethiopia in the context of the 1000 Genome Project dataset to get at this question, hypothesizing that individuals from either location would be closer “related” to Eurasians. Key findings of this study include (a) 80% of non-African ancestry in Egyptians, dated to ~750 ybp, coinciding with the Islamic expansion, (b) varying levels (up to 50%) non-African ancestry in Ethiopians, with admixture dating back to 2,500-3,000 ybp, (c) more predominant Egyptian haplotypes in CHB (Han Chinese) and Toscani Italian (TSI) samples, pointing to a northern route (via Egypt), contributing to greater levels of ancestry outside of Africa.

These findings point to the northern route as the preferential direction taken out of Africa. In doing this, they resolve the puzzles of archaeological similarities and Neandertal admixture, which are readily accommodated by a northern-exit model, but not by a southern exit, and fit well with the recent discovery of human remains dating to around 55,000 years ago in Israel (close to the northern route)

Neolithic sculptures from the Yamnaya culture.

Neolithic sculptures from the Yamnaya culture.

Continuing the story from above, as modern humans migrated out of Africa via Egypt into Eurasia, much less is known about the migratory epochs of the Bronze Age (3000-1000 BC). Alltentoft et al. (2015) sequence whole genomes of 101 Eurasian archaeological samples, and analyze population genomic history using admixture statistics.

Findings of Allentoft et al. (2015) depicting routes of migration of the Yamnaya culture into Europe and Asia. Image courtesy: Figure 1 of Alltentoft et al. (2015).

Findings of Allentoft et al. (2015) depicting routes of migration of the Yamnaya culture into Europe and Asia. Image courtesy: Figure 1 of Alltentoft et al. (2015).

Findings from this study include (a) Caucasian admixture early on into hunter-gatherers and Neolithic farmers in north-central Europe, coinciding with the expansion of the Yamnaya into Europe (b) a tandem Yamnaya expansion eastward into Asia, (c) fixation of light skin pigmentation SNP’s in Europeans during the Bronze Age, and (d) low frequencies of lactose tolerance alleles despite high tolerance in present-day Europeans.

 

We show that the Bronze Age was a highly dynamic period involving large-scale population migrations and replacements, responsible for shaping major parts of present-day demographic structure in both Europe and Asia.

References:

Allentoft ME. et al. (2015) Population genomics of Bronze Age Eurasia. Nature, June 2015. DOI: http://dx.doi.org/10.1038/nature14507

Pagani L. et al. (2015) Tracing the Route of Modern Humans out of Africa by Using 225 Human Genome Sequences from Ethiopians and Egyptians. AJHG Volume 96, Issue 6, p986-991. DOI: http://dx.doi.org/10.1016/j.ajhg.2015.04.019

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About Arun Sethuraman

I am a computational biologist, and I build statistical models and tools for population genetics. I am particularly interested in studying the dynamics of structured populations, genetic admixture, and ancestral demography.
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