The peopling of the Himalayas may be quite late relative to other areas of eastern Eurasia, being settled only in the past 5000–7000 years (Huang, 1994). This region is now occupied by many populations speaking Sino-Tibetan languages. Tibetan speakers, including Monba, Bhutanese, Sikkimese, and northern tribes in Nepal (Lewis, 2009), reside in the western Himalayas, and can trace their origins back to the Tibetan expansion in the recent 2000 years (Huang, 1994). In the eastern Himalayas between Tibet and Assam, two main populations reside in the region, the Luoba (synonym of Adi) and Deng (synonym of Mishmi) (Kang et al., 2010). However, we know very little about how and when the Luoba and Deng arrived in this region. The languages of these two populations belong to the North Assam branch of the Sino-Tibetan language family, and thus provide no clear evidence for their origins. Therefore, we investigated genetic diversity in these populations to clarify their origins and biological relationships to other Sino-Tibetan groups.
The best genetic systems to use for tracing population history are the Y chromosome (Jin & Su, 2000; Underhill et al., 2000; Jobling & Tyler-Smith, 2003) and the mitochondrial DNA (Wallace, 1994). The mitochondrial DNA data from the region of the Tibetan Plateau and the Himalayas have revealed that there have been multiple population expansions into the plateau (Fornarino et al. 2009; Qin et al., 2010), although these data have provided limited information about the migration routes into the Himalayas. Therefore, we attempted to elucidate the population origins of the Luoba and Deng by studying their Y-chromosome diversity, since the Y chromosome has diversified into dozens of haplogroups among the world populations (Y-Chromosome-Consortium, 2002).
Among these paternal lineages, haplogroup O3 is the dominant haplogroup in Sino-Tibetan populations (Shi et al., 2005), and therefore, is the most useful paternal lineage for studying the expansion history of Sino-Tibetan populations. In this paper, we investigated Y-chromosome variation in the Luoba and Deng people, and analyzed the phylogeography of haplogroup O3, to explore the migration routes of Sino-Tibetan people into the eastern Himalayas. Our data suggest at least two migration routes from North China into this region.