Post by djoser-xyyman on Aug 17, 2010 12:23:34 GMT -5
Report
Independent Origins of Indian Caste and Tribal Paternal Lineages
Richard Cordaux , a, 5, , Robert Aungerb, Gillian Bentleyc, Ivane Nasidzea, S.M. Sirajuddind and Mark Stonekinga
aMax Planck Institute for Evolutionary Anthropology, D-04103 Leipzig, Germany
bEnvironmental Health Group, London School of Hygiene and Tropical Medicine, London WC1E 7HT, England
cDepartment of Anthropology, University College London, London WC1E 6BT, England
dAnthropological Survey of India, Mysore 570002, Karnataka State, India
Received 24 June 2003;
revised 3 November 2003;
accepted 18 December 2003.
Published: February 3, 2004.
Available online 5 February 2004.
The origins of the nearly one billion people inhabiting the Indian subcontinent and following the customs of the Hindu caste system [1.] and [2.] are controversial: are they largely derived from Indian local populations (i.e. tribal groups) or from recent immigrants to India? Archaeological and linguistic evidence support the latter hypothesis [2.], [3.] and [4.], whereas recent genetic data seem to favor the former hypothesis [5]. Here, we analyze the most extensive dataset of Indian caste and tribal Y chromosomes to date. We find that caste and tribal groups differ significantly in their haplogroup frequency distributions; caste groups are homogeneous for Y chromosome variation and more closely related to each other and to central Asian groups than to Indian tribal or any other Eurasian groups. We conclude that paternal lineages of Indian caste groups are primarily descended from Indo-European speakers who migrated from central Asia 3,500 years ago. Conversely, paternal lineages of tribal groups are predominantly derived from the original Indian gene pool. We also provide evidence for bidirectional male gene flow between caste and tribal groups. In comparison, caste and tribal groups are homogeneous with respect to mitochondrial DNA variation [5.] and [6.], which may reflect the sociocultural characteristics of the Indian caste society.
Results and Discussion
Earlier genetic studies discussing the origins of Indian caste groups have included at best a few tribal groups for comparison [5.], [7.], [8.] and [9.]. Although they constitute only 8% of the total Indian population, tribal groups are generally considered to be the aboriginal inhabitants of the Indian subcontinent, present in the region before the arrival of Indo-European speakers [2]. As such, they represent a unique source for estimating the in situ pre-Indo-European genetic diversity of India as well as for investigating the origins of caste populations of India. Recently, a qualitative comparison of presence versus absence of Y chromosome haplogroups in just two tribal and six caste groups led to the conclusion that both Indian caste and tribal Y chromosomes largely derive from the same Pleistocene genetic heritage, with only limited recent gene flow from external sources. This conclusion implies an in situ origin of paternal lineages of caste groups [5], which is at odds with nongenetic evidence [2.], [3.] and [4.].
To determine if Indian caste paternal lineages are derived from local ancestors (i.e., tribal groups) or from other Eurasian source(s), we obtained new Y chromosome data from 155 individuals from nine tribal groups and one caste group and compared these to published data [5.], [9.] and [10.]. The total dataset consists of 931 Y chromosomes from 15 tribal and 12 caste groups and constitutes the most extensive dataset of Indian Y chromosomes to date. The studied caste groups originate from all over India, whereas the tribal groups were sampled only from southern India. Tribal groups from elsewhere were not included as most of them inhabit the Indo-European-speaking sphere and hence may not reflect the pre-Indo-European genetic composition of India.
Thirteen haplogroups were observed in India (Figure 1). The seven most frequent haplogroups account for 80%–90% of both caste and tribal Y chromosomes, suggesting an extensive overlapping of caste and tribal Y chromosome variation, as found previously [5]. However, the frequency distribution of these haplogroups is significantly different between tribal and caste groups (÷2 = 134.1, degrees of freedom [d.f.] = 7, p < 0.001). At a finer scale, the same trend is observed in that tribal groups differ significantly from both northern (÷2 = 132.5, d.f. = 7, p < 0.001) and southern (÷2 = 94.1, d.f. = 7, p < 0.001) Indian caste groups.
