Eurasian migration steppe by steppe

Geographical features represent a strong barrier to human gene flow across inner Eurasia, genetic research has revealed.

Researchers led by Choongwon Jeong of the Max Planck Institute for the Science of Human History, in Jena, Germany, collected genome samples from 763 indigenous people in the tundra, forests and steppe to build a picture of prehistoric population flows through the vast Inner Eurasia region.

As well as samples from 60 ethnic groups in nine countries – Armenia, Georgia, Kazakhstan, Moldova, Mongolia, Russia, Tajikistan, Ukraine and Uzbekistan – the team also included data from the 5000-year-old remains of two people from Kazakhstan’s ancient Botai culture to find links with today’s indigenous groups.

The findings, reported in the journal Nature, reveal “a striking correlation between genes, geography and language”, the researchers write.

The data shows Inner Eurasian populations are structured into three distinct clines – variations in a single biological trait present in a group of people – and that these mirror geographic regions. 

The clines run from east to west in three bands.

A northern band runs through the Arctic tundra and boreal forests. This population has the clearest genetic affinity with early hunter-gatherers known as Ancient North Eurasians, and is also strongly linked to Native Americans.

A middle band runs through the southern forests and steppe. This population shows Late Bronze Age steppe ancestries linked to both western herders and people from the Amur River basin on the border of modern Russia and China.

Finally, a southern band corresponds to the lower steppe and shrubland region. This population shows a strong West and South Asian influence, linking it to Mesolithic Caucasus hunter-gatherers and Neolithic Iranians.

The data shows “substantial separation” between the ancestries of these groups, the researchers conclude.

The clines also correspond to language distribution. The northern cline includes all Uralic and Yeniseian speakers, while the other two include Turkic and Mongolic speakers.

The findings identify geographic barriers to gene flow through the region. In particular, the 1100-kilometre long Caucasus mountain ranges, stretching from the Black Sea to the Caspian Sea, have posed a strong barrier to human migration in the region, and therefore to gene flow. This is reflected in the genetic structure of Caucasus populations north and south of the mountains.

Jeong  and colleague report that while it is known that the region’s populations have changed greatly over millennia, there is limited information about how environmental and cultural influences are reflected in the genes of modern-day Inner Eurasians.

Waves of migration make pinning down genetic histories in the region difficult, and work on the three clines is far from complete, the researchers say.

“Inner Eurasia has functioned as a conduit for human migration and cultural transfer since the first appearance of modern humans in this region,” they write.

“As a result, we observe deep sharing of genes between Western and Eastern Eurasian populations in multiple layers.

“It will be extremely important to expand the set of available ancient genomes across Inner Eurasia.”