The Genetic Legacy of Zoroastrianism in Iran and India: Insights into Population Structure, Gene Flow, and Selection

Saioa López,Mark G Thomas,Lucy Van Dorp,Naser Ansari-Pour,Sarah Stewart,Abigail L Jones,Erik Jelinek,Lounès Chikhi,Tudor Parfitt,Neil Bradman,Michael E Weale,Garrett Hellenthal

doi:10.1016/j.ajhg.2017.07.013

Abstract

Zoroastrianism is one of the oldest extant religions in the world, originating in Persia (present-day Iran) during the second millennium BCE. Historical records indicate that migrants from Persia brought Zoroastrianism to India, but there is debate over the timing of these migrations. Here we present genome-wide autosomal, Y chromosome, and mitochondrial DNA data from Iranian and Indian Zoroastrians and neighboring modern-day Indian and Iranian populations and conduct a comprehensive genome-wide genetic analysis in these groups. Using powerful haplotype-based techniques, we find that Zoroastrians in Iran and India have increased genetic homogeneity relative to other sampled groups in their respective countries, consistent with their current practices of endogamy. Despite this, we infer that Indian Zoroastrians (Parsis) intermixed with local groups sometime after their arrival in India, dating this mixture to 690–1390 CE and providing strong evidence that Iranian Zoroastrian ancestry was maintained primarily through the male line. By making use of the rich information in DNA from ancient human remains, we also highlight admixture in the ancestors of Iranian Zoroastrians dated to 570 BCE–746 CE, older than admixture seen in any other sampled Iranian group, consistent with a long-standing isolation of Zoroastrians from outside groups. Finally, we report results, and challenges, from a genome-wide scan to identify genomic regions showing signatures of positive selection in present-day Zoroastrians that might correlate to the prevalence of particular diseases among these communities.

Highlights

Zoroastrianism developed from an ancient religion that was once shared by the ancestors of tribes that settled in Iran and northern India and is thought to have been founded by the prophet priest Zarathustra (Zoroaster in Greek)
Zoroastrians Are Genetically Differentiated from NonZoroastrians, with Different Historical Ancestry in Parsis Relative to Non-Zoroastrian Indians Most of the Iranian Zoroastrians are positioned within the autosomal genetic variation of other sampled Iranian samples in a Principal Component Analysis (PCA) of West Eurasian individuals (Figure S4)
Though there are further splits of our final Iranian and Indian Zoroastrian clusters if we increase the number of clusters beyond 51, we note that individuals within each of our final assigned Zoroastrian clusters are very genetically similar to one another

Summary

Introduction

Zoroastrianism developed from an ancient religion that was once shared by the ancestors of tribes that settled in Iran and northern India and is thought to have been founded by the prophet priest Zarathustra (Zoroaster in Greek). According to Parsi (i.e., Indian Zoroastrians) tradition, a group of Zoroastrians set sail from Iran to escape persecution by the Muslim majority. They landed on the coast of Gujarat (India) where they were permitted to stay and practice their religion. The Indian Zoroastrians maintained contact with the Zoroastrians of Iran and later became an influential minority under British Colonial rule

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