The search for the cradle of horse domestication goes on

Mitochondrial and coat color diversity before (top) and after (bottom) 2000 BCE. The left side shows the evolution of mitochondrial haplotype diversity of horses in Anatolia and the southern Caucasus. At right shows the evolution of coat color genetic diversity in these two geographic regions in the same time ranges. The area of the circles is proportional to the number of individuals present in each category. Image:

The origins of horse domestication will remain a mystery for now, after researchers ruled out a region held up as a strong candidate.

Despite the important roles that horses have played in human history, the origins of domestic horses remain elusive.

Several regions have been hypothesized, but most have been invalidated through recent studies of ancient genes.

Anatolia is a region with a long history of horses that has been considered a candidate for the origins of their domestication. Anatolia is the peninsula known as Asia Minor, and comprises most of Turkey.

Researchers, reporting in the journal Science Advances, conducted extensive testing of ancient horse DNA to determine if Anatolia and the southern Caucausus were the cradle of horse domestication.

Their analysis of horse DNA ranged from the Neolithic to the Iron Age (around 8000 to about 1000 BCE), encompassing the period in which horses transitioned from wild to domestic, around 4000 to 3000 BCE.

In all, testing was conducted on 111 equid remains, with 60 successfully genotyped.

The research, led by Silvia Guimaraes from the Institut Jacques Monod in Paris, ruled out Anatolia as the root of horse domestication.

Their genetic work revealed the rapid and large-scale introduction of domestic horses at the end of the third millennium BCE, which argued strongly against independent domestication of horses in the region.

“Our results allow us to conclude that domestic horses were introduced into the Caucasus and Anatolia by at least 2000 BCE, presumably from the Eurasian steppes.”

This conclusion is based on the fact that DNA before about 4500 BCE carried only two mitochondrial haplogroups, which suggested a local wild population, with little or no gene flow from neighboring wild horse populations because of geographical barriers.

“Our study provides the first evidence showing that Anatolia was home to a genetically distinct population of wild horses, which, based on archaeozoological findings, were widely exploited during the Neolithic and Chalcolithic periods,” they reported.

Around 2000 BCE, there was a statistically significant decline in the frequency of this local wild horse mitochondrial signature. One of the two haplogroups became rare and the other disappeared completely.

Parallel to this, the diversity of maternal lineages in archaeological horse remains from the Caucasus and Anatolia increased markedly from this time.

The genetic changes seen do not reflect a gradual process involving the local population, they said, but rather a sudden appearance around 2000 BCE of nonlocal lineages that are still present in domestic horses.

Their findings also showed that these imported horses exhibited coat colors that were absent in the local wild horses before domestication.

They concluded: “Our results strongly suggest that Anatolia was not a primary source for domestic horse lineages, but, as observed in other regions, local matrilines were incorporated into herds of imported domestic horses, which were also hybridized with local donkeys to create mules.

“The ultimate geographic origins of the imported domestic herds remain to be determined, but eliminating Anatolia as a source of domestication directs further attention to the adjacent regions of the Black Sea.”

Ancient DNA shows domestic horses were introduced in the southern Caucasus and Anatolia during the Bronze Age
Silvia Guimaraes et al. Science Advances 16 Sep 2020: Vol. 6, no. 38, eabb0030 DOI: 10.1126/sciadv.abb0030

The study, published under a Creative Commons License, can be read here

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