How Did the Mongol Invasions Change Population Genetics?
Invasions and wars often cause the most dramatic and radical changes to cultures and history in many regions. However, it is not just the social transformations they bring but often the physical, genetic makeup of populations change. Whether it is through forced migrations, interbreeding, or simply high casualties from war or disease, there are important impacts to populations in times of great upheaval such as wars. The Mongol Invasions (1206–94) represent an important event in the history of population genetics because of the large, spatial extent of the invasions that spanned across Eurasia.
The Mongol conquests of the 13th century once spanned across areas of what are Poland to Korean, incorporating major regions and states such as China, Iran, and large areas of Russia (Figure 1). Overall, the Mongol Empire represents the second largest empire known, perhaps second to the British Empire of the 19th century. This great expanse gave great opportunities for large-scale movement, not only of the Mongols but also other populations within this large empire. The corridors in the Mongol Empire meant that parts of east Asia and Europe were directly linked for the first time. 
Evident Genetic Changes
Studies have indicated that Genghis Khan himself may have been among history's most prolific influences on populations, where his genes could have influenced up to 8% of the male population in Asia today. However, tracing to a specific individual might be difficult, thus the genes attributed to Genghis Khan could actually be more representatives of his genetic group. Overall, what is evident is that Y-chromosomal lineage variation in populations can be found in 16 populations in Asia that span from the Pacific to the Caspian. In effect, this variation is relatively unusual and often is characteristic for small groups of populations. This variation is from a limited group from Mongolia. Additionally, in the study, it is clear this population spread rapidly and far, spreading what should have been a more limited chromosomal variation, which suggests that the chromosomal changes happened due to migration (Figure 2).
Another study has showed that such genetic variation could be extended further, where genetic traits associated with Mongol populations could also be found in Turkey and the Middle East. Turkic and Mongol groups show close affinity in places, cultural and genetically, where the former likely expanded even further within Central Asia and Western Asia as they were closely associated with the Mongols. This is evident in the genetic makeup in some Turkic populations that show close connections with Mongols but also that they did migrate to Western regions. In effect, other groups such as the Turks seem to be spreading in the period of Mongol dominance
In fact, it seems Turkic populations may have been the largest group to benefit from the invasions, as their haplogroups a few centuries after the invasions could be found even in Eastern Europe, the Middle East, Northern Caucasus, Central Asia, Southern Siberia, Northern China, and Northeastern Siberia. On the other hand, studies that have looked for the origin of Turkic groups have identified a far more limited region, around Mongolia and South Siberia. Over a period from the lst millenium CE to the mid 2nd millennium CE there does seem to be a rapid spread of Turkic groups and population across Eurasia in particular. In effect, while the Turkic populations had begun to expand even prior to the Mongol invasions, they expanded even more greatly and rapidly during and after the invasions.
While migration of Turkic populations was one outcome, another outcome was the depopulation of regions, particularly in Western Asia and parts of Europe. These regions, as they resisted the Mongols fiercely, also witnessed the greatest retribution due to their opposition. In these cases, with whole populations of cities sometimes destroyed possibly destroyed, or at least fighting men, migration as well as intermarriage between new populations likely caused an overall change in the population makeup of these regions. However, as historical sources may exaggerate destruction, it is not clear how extensive the depopulation of regions were. It is evident that once populated cities such as Baghdad and Merv were significantly reduced, but how extensive this occurred to the surrounding region is unclear. What one could conclude is that population genetic change probably included a combination of migration, interbreeding, but also replacement of the population where at least parts of the previous population were killed off and replaced by new comers.
Historical and Genetic Impact
The genetic impact is clear, where Turkic and, to some extent, Mongol genetic markers are found in a much wider region than one would expect. However, while the Mongol invasions did bring new DNA, indigenous DNA are still a strong factor in many populations, such as in Turkey, suggesting that intermixed populations (i.e., intermarrying) emerged more commonly in places rather than complete population replacement in regions. Thus, overall, we see in many parts of Asia that the population genetics did shift, in composition as relatively rare traits becoming more common. This included the population in much of Eurasia becoming more Turkic, in part replacing some of the Indo-Aryan influences from earlier periods that were more common. This is evident linguistically in Central Asia and West Asia today, where Turkish and Turkic languages have become more dominant relative to the Indo-Aryan group of languages that had emerged as early as the 2nd millennium BCE and once spread from India to Europe. The linguist shift was not, however, a major cultural shift outside of lanugage, as many of the Turkic populations adopted Islam and other religions in areas where other populations were prominent. Overall, the impact is one of population and linguistic shifts rather than fulscale cultural replacement. In effect, the cultural impacts were not as dramatic as the genetic changes in places.
Invasions have shifted human history in many ways. The genetic shifts represent a physical manifestation of how populations shifted or changed as new migrants arrived or were displaced and moved around. The shifts that occurred in the Mongol period are a clear indication of large-scale expansion of a limited number of groups, namely Mongols and Turks, across much of Eurasia. The expansion of Turkish and Turkish successor states are one evident result of this; however, the cultural changes were more minimal, as the new populations often adopted the cultures and religions of the groups they integrated with. Population makeup did shift, as new genetics were introduced into the older population genetic makeup.
- For more on the history and background to the Mongol Empire and populations, see: Fitzhugh, William W, Morris Rossabi, William Honeychurch, and Arctic Studies Center. 2013. Genghis Khan and the Mongol Empire.Odyssey Books & Maps with Smithsonian Institution.
- For more on the Y-chromosomal study, see: Zerjal, Tatiana, Yali Xue, Giorgio Bertorelle, R. Spencer Wells, Weidong Bao, Suling Zhu, Raheel Qamar, et al. 2003. “The Genetic Legacy of the Mongols.” The American Journal of Human Genetics 72 (3): 717–21. doi:10.1086/367774.
- For more on Turkic and Mongol genetic affinity, see: Bai, Haihua, Xiaosen Guo, Dong Zhang, Narisu Narisu, Junjie Bu, Jirimutu Jirimutu, Fan Liang, et al. 2014. “The Genome of a Mongolian Individual Reveals the Genetic Imprints of Mongolians on Modern Human Populations.” Genome Biology and Evolution 6 (12): 3122–36. doi:10.1093/gbe/evu242.
- For more on Turkic populations and their genetics, see: Yunusbayev, Bayazit, Mait Metspalu, Ene Metspalu, Albert Valeev, Sergei Litvinov, Ruslan Valiev, Vita Akhmetova, et al. 2015. “The Genetic Legacy of the Expansion of Turkic-Speaking Nomads across Eurasia.” Edited by Graham Coop. PLOS Genetics 11 (4): e1005068. doi:10.1371/journal.pgen.1005068.
- For more on death rates due to the Mongol invasions, see: Saunders, J. J. 2001. The History of the Mongol Conquests. Philadelphia: University of Pennsylvania Press.
- For a look into how the genetic and other social changes that occurred are evident, see: Di Cosmo, Nicola, Allen J Frank, and Peter B Golden. 2015. The Cambridge History of Inner Asia. Cambridge: Cambridge University Press.