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. 2022 Jan 14;12(1):733.
doi: 10.1038/s41598-021-04144-4.

Genetic continuity of Indo-Iranian speakers since the Iron Age in southern Central Asia

Perle Guarino-Vignon  1   2 , Nina Marchi  3   4 , Julio Bendezu-Sarmiento  3   5 , Evelyne Heyer  3 , Céline Bon  3
Affiliations

Genetic continuity of Indo-Iranian speakers since the Iron Age in southern Central Asia

Perle Guarino-Vignon et al. Sci Rep. .

Abstract

Since prehistoric times, southern Central Asia has been at the crossroads of the movement of people, culture, and goods. Today, the Central Asian populations are divided into two cultural and linguistic groups: the Indo-Iranian and the Turko-Mongolian groups. Previous genetic studies unveiled that migrations from East Asia contributed to the spread of Turko-Mongolian populations in Central Asia and the partial replacement of the Indo-Iranian populations. However, little is known about the origin of the latters. To shed light on this, we compare the genetic data on two current-day Indo-Iranian populations - Yaghnobis and Tajiks - with genome-wide data from published ancient individuals. The present Indo-Iranian populations from Central Asia display a strong genetic continuity with Iron Age samples from Turkmenistan and Tajikistan. We model Yaghnobis as a mixture of 93% Iron Age individual from Turkmenistan and 7% from Baikal. For the Tajiks, we observe a higher Baikal ancestry and an additional admixture event with a South Asian population. Our results, therefore, suggest that in addition to a complex history, Central Asia shows a remarkable genetic continuity since the Iron Age, with only limited gene flow.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Geographic and genetic structure of our dataset. (a) Map of the published ancient samples in our dataset (Map generated using ggmap and Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL). (b) PCA computed on a set of 236,566 SNPs for present-day Eurasians populations including 527 present-day Central Asian individuals genotyped on an 300k SNPs array and we projected the 3102 ancient genomes onto the two first Principal Components. Ancient genomes are represented with different colors by region, with density line to facilitate the reading. (c) Details of panel (b) focusing on Indo-Iranians individuals with ancient individuals from Neolithic, Bronze Age, Iron Age and Historical times. (Figures done with ggplot2 v. 3.3.3 R package https://cran.r-project.org/web/packages/ggplot2/index.html).
Figure 2
Figure 2
ADMIXTURE analysis of 5019 individuals (3102 ancient and 1915 modern). The results for a subset of the dataset (present-day Indo-Iranian individuals and ancient populations discussed in the main text) are displayed for K = 10, which has the lowest cross validation value (0.994). The full analysis is shown in SI. In the first column, the modern individuals from Central Asia; second column, the ancient individuals from southern Central Asia; third column, ancient individuals from the Steppe; last column, miscellaneous individuals discussed in the main text. (Figure done with ggplot2 v. 3.3.3 R package https://cran.r-project.org/web/packages/ggplot2/index.html).
Figure 3
Figure 3
Gene flow in Indo-Iranian populations since Iron Age. Positive D-statistics (Z > 3) of the form D(Mbuti, Ancient population; Turkmenistan_IA, TJY/TJE/TUR). A positive D-statistic demonstrates that a gene flow occurred from the ancient population to the Indo-Iranian or Turkmen population compared to Turkmenistan_IA. The estimated statistic ± 3 standard errors is indicated. (Figure done with ggplot2 v. 3.3.3 R package https://cran.r-project.org/web/packages/ggplot2/index.html).
Figure 4
Figure 4
Absence of affinity of Turkmenistan_IA with East Asia ancestry shown by D-stat. In grey are non-significative (Z < 3) D-statistics, in blue significative positive D-statistics and in red significative negative one. Only populations with strong East Asian or BHG ancestry show a significative D-statistic. (Figure done with ggplot2 v. 3.3.3 R package https://cran.r-project.org/web/packages/ggplot2/index.html).
Figure 5
Figure 5
Turkmens’ affinity with Tajiks rather than with Turko-Mongol groups shown by f3 statistics of the form f3(Mbuti; TUR/TJA/AKZ , Ancient population). (A) Outgroup f3-statistics for Turkmen and for Tajiks (TJA) plotted against each other. (B) Outgroup f3-statistics for Turkmen and for Kazakhs (AKZ), belonging to the Turko-Mongol group, plotted against each other. (Figure done with ggplot2 v. 3.3.3 R package https://cran.r-project.org/web/packages/ggplot2/index.html).
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