Wednesday, November 18, 2015

The Mystery of European Ancestry

Fig.1.  DNA was extracted from molar teeth of this skeleton dating almost
10,000 years ago, found in Western Georgia (
Credit: Eppie Jones)

Between 4,800 and 5,000 years ago, nomadic herders swept through Europe from the vast steppe in modern-day Russia and Ukraine. These herders, part of the Yamnaya culture, made up one of three ancestral populations that formed the genetic structure of contemporary European populations. Yet findings published on Monday in the journal Nature Communications provide new details to this history and suggest that a previously unknown “fourth strand” of ancient European ancestry existed.

Secret History of the Caucasus

The story of the mysterious fourth group came to light through ancient DNA recovered from two skeletons in Georgia, dating between 9,700 and more than 13,000 years old. An international team led by researchers from Trinity College Dublin, University College Dublin, and Cambridge University compared the skeletons’ genomes to another ancient skeleton from Switzerland, as well as those of modern-day Eurasian populations.

The genetic differences between both the ancient and more recent populations allowed the researchers to create a timeline of migration into Europe. Around 45,000 years ago, a group of hunter-gatherers left Africa and split off north to settle in the Caucasus region. This lineage became increasingly isolated in the mountains of the Caucasus, weathering the Last Glacial Maximum (LGM) over 25,000 years ago alone. Once thawing began, the population came into contact with other people farther east, resulting in the horse-borne Yamnaya culture.

According to Dr. Andrea Manica, the lead senior author with Cambridge University, this analysis fills in a very important part of the Yamnaya history. Recent studies have suggested that the Yamnaya may have brought the Proto-Indo-European tongue to Europe, catalyzing the formation of modern Indo-European languages. The same studies also link the arrival of the wheel in Europe and early mutations for lactose tolerance to these travelers from the east. Their specific origin in the east, however, was a mystery before this week.

Fig.2. The Caucasus mountains of Georgia helped to isolate
hunter-gatherers during the LGM (
Credit: Ronan Shenhav via Flickr, 2015

Human Migration and Palaeontology Collections

The discovery does not just contribute to our understanding of human evolution in Europe, but rather to human migration in Asia, as well. Researchers found that the closest match to the ancient Caucasus genomes existed in modern Indian populations. This suggests that in addition to traveling west towards Europe, the Yamnaya or the Caucasus group went south into the Indian subcontinent and possibly even farther east.

Ultimately, the Georgian skeletons provided details for a rich history of humans after they left Africa. David Lordkipanidze, co-author and general director of the Georgian National Museum, points to this case as an example of the in-depth palaeogenetic information hidden in Georgia’s extensive fossil collection. In addition to local fossil use, the study drew from previous literature and online resources for a comprehensive analysis of ancestral and modern populations. Both associated data and advances in ancient DNA technology allow unprecedented opportunities to mine the collections for new hints to our ancient past.


References:
Deane, T. (2015, November 15). Scientists fill in the gaps of human hunter-gatherer history [press release]. EurekAlert! Retrieved from http://www.eurekalert.org/pub_releases/2015-11/tcd-sfi111315.php

Gibbons, A. (2015, June 10). Nomadic herders left a strong genetic mark on Europeans and Asians. Science. Retrieved from http://news.sciencemag.org/archaeology/2015/06/
nomadic-herders-left-strong-genetic-mark-europeans-and-asians

Jones, E. R., et al. (2015, November 16). Upper Palaeolithic genomes reveal deep roots of modern Eurasians. Nature Communications, vol. 6 (8912). doi:10.1038/ncomms9912

Lazaridis, I., et al. (2014, September 17). Ancient human genomes suggest three ancestral populations for present-day Europeans. Nature, vol. 513: 409-413. doi: 10.1038/nature13673



Glossary

Caucasus
A region between the Black Sea and the Caspian Sea at the border of Europe and Asia.
Last Glacial Maximum (LGM)
Period of time during the last glaciation in which the ice sheets were at their greatest extension. The maximum positions were reached 26,500 years ago and then deglaciation started around 19,000 years ago in the Northern Hemisphere.

No comments :

Post a Comment