Original Research Article Genetic Heterogeneity in Northeastern India: Reflection of Tribe–Caste Continuum in the Genetic Structure VIKRANT KUMAR, 1 DEBASHIS BASU, 2 AND B. MOHAN REDDY 1 * 1 Anthropology and Human Genetics unit, Indian Statistical Institute, Kolkata, India 2 Anthropological Survey of India, North-Eastern Regional Center, Shillong, India ABSTRACT We critically examined the gene frequency data for 11 genetic markers commonly available in the literature for 22 populations of northeastern India in the light of their geographic, linguistic, and ethnic affiliations. The markers investigated were three blood groups (A 1 A 2 BO, MNS, and Rh), four serum proteins (KM, Gc, Hp, and Tf), and four enzyme systems (AP, AK, EsD, and Hb). The neighbor-joining tree and multidimensional scaling of the distance matrix suggest rela- tively high genetic differentiation among the Mongoloid groups, with probably diverse origins when compared to the Caucasoid Indo-European populations, which had probably come from relatively more homogeneous backgrounds. Broadly speaking, the pattern of population affinities conforms to the ethno-historic, linguistic, and geographic backgrounds. An interesting and important feature that emerges from this analysis is the reflection of the effect of the sociological process of a Tribe– Caste continuum on genetic structure. While on one end we have the cluster of Caucasoid caste populations, the other end consists of Mongoloid tribal groups. In between are the populations which were originally tribes but now have become semi-Hinduized caste groups, viz., Rajbanshi, Chutiya, and Ahom. These groups have currently assumed caste status and speak Indo-European languages. Therefore, one may infer that what appears to be a purely sociological phenomenon of a Tribe–Caste continuum may well reflect in their genetic structure. Am. J. Hum. Biol. 16:334–345, 2004. # 2004 Wiley-Liss, Inc. The northeastern part of India is inhabited by numerous endogamous tribes and castes that have their own distinct social, linguistic, and biological identity. It has been hypothe- sized that a plethora of migrations, particu- larly through the northeast Indian corridor, has contributed to the present-day population of northeastern India. Ethnically speaking, most of the tribal groups are Mongoloids, whereas caste groups are either Caucasoids or show a mosaic of features of both the eth- nic groups. The Mongoloids/Indo-Mongoloids have come to India from different directions at different times and perhaps earlier than the Caucasoids (Das et al., 1987). While the Mongoloids have migrated from eastern, southeastern (Rapson, 1955; Dani, 1960), and central Asian regions, the Caucasoids may have entered from western and northern boundaries of this region. While a majority of the Mongoloids are tribes affiliated with the Tibeto-Chinese linguistic family, except- ing Khasi, most of the Caucasoids are caste groups and speak Indo-European languages. Although these groups have been broadly classified on the basis of language and ethnicity, they show considerable variations within these broad categories. Both the Mongoloid and Caucasoid groups show a cer- tain degree of differentiation within them- selves in cultural and biological traits such as anthropometry, genetic markers, and derma- toglyphics (Das, 1971, 1973, 1979; Phookan, 1974; Das and Das, 1981; Roychoudhury, 1992; Bhasin and Walter, 2001). Further, the Caucasoid and Mongoloid populations have cohabited for a long time and presumably there was gene flow between them, as is evident from the conclusions drawn in many studies (Das, 1977; Das et al., 1980a,b). A number of studies using traditional genetic markers (Bhasin et al., 1986; Singh ß 2004 Wiley-Liss, Inc. *Correspondence to: B. Mohan Reddy, Ph.D., Professor, Anthropology and Human Genetics Unit, Indian Statistical Institute, 203, B.T. Road, Kolkata – 700 108, India. E-mail: bmr@isical.ac.in Received 23 July 2003; Revision received 22 December 2003; Accepted 22 January 2004 Published online in Wiley InterScience (www.interscience. wiley.com). DOI: 10.1002/ajhb.20027 AMERICAN JOURNAL OF HUMAN BIOLOGY 16:334–345 (2004)