Australia: The Land Where Time Began

A biography of the Australian continent 

The Genetic Diversity and Phylogenetic Affinities of the Soliga, an Isolated Tribe in Southern India

This study was carried out to investigate the role of tribal people, the earliest inhabitants of India, in order to determine their role, if any, in the dispersal of anatomically modern humans. The Soliga people are a tribal group living in the Biligiri Rangana Hills, southern India, who are believed to possibly be among India’s first settlers. This group of forest-bound people speak Dravidian, practicing a subsistence level agriculture under primitive conditions in an isolated location. This study examined the phylogenetic relationships of the Soligas in relation to 29 worldwide, reference populations that were geographically targeted. Morlote et al. employed a battery of 15 hypervariable autosomal short tandem repeat loci as markers. It was found that the Soliga tribe were remarkably different from other populations of India including other tribes of southern India who speak Dravidian. Contrasting with this, the Soliga people exhibited a genetic affinity to 2 populations of Australian Aboriginal people. Morlote et al. suggest that this genetic similarity could be attributed to the ´Out of Africa´ migratory wave(s) along the southern coast of India that eventually reached Australia. An alternative possibility is that the genetic affinity that has been observed may be explained by more recent migrations from the Indian subcontinent to Australia.

A number of studies have supported the pivotal role of India in the dispersal of anatomically modern humans (Quintana-Murci et al., 1999; Redd & Stoneking, 1999; Ingman et al., 2000; Redd et al., 2002; Basu et al., 2003; Cordaux et al., 2004; Macaulay et al., 2005; Thangaraj et al., 2005; Sun et al., 2006; Majumder, 2010). It is suggested by archaeological and genetic data that the extensive coastal area of India may have served as a route followed by human populations as they migrated out of Africa about 70 ka (70 thousand years ago) and settled in Southeast Asia and Australia (Quintana-Murci et al., 1999; Macaulay et al., 2005; Sun et al., 2006; Kennedy et al., 1987; Cavalli-Sforza, 1994; Lahr & Foley, 1994; Stringer, 2000; Cann, 2001; Maca-Meyer, 2001; Lewin & Foley, 2004; Palanichamy et al., 2004; Tanaka, 2004; Kong et al., 2006). More than a century ago Huxley (Huxley, 1870) noticed the similarities between some Indian tribes and Australian Aboriginal people, leading him to suggest an India-Australian connection. The physical similarities were attributed by Birdsell (Birdsell, 1993) to a possible migration of people with affinities to tribal Indians into Australia about 15,000 BP. Birdsell hypothesised that various migratory waves shaped the peopling of Australia. Birdsell (Birdsell, 1993) proposed that the Carpentarians, people with physical characteristics that were similar to the Vedda Tribe of South India and Sri Lanka, arrived through the Gulf of Carpentaria about 15,000 BP and colonised northern and central Australia.

A mtDNA study that argued for a recent link between Aboriginal Australia and populations from the Indian subcontinent, supported Birdsell’s ‘multiple migrations’ hypothesis. A study by Redd et al. later reported the presence of a paragroup C-M216* Y-chromosome in both India and Australia, proposing a mid-Holocene common ancestry for these chromosomes. It is suggested by this genetic data that multiple migrations were also supported by changes in the anthropological record of Australia between 5,000 and 3,000 BP. Included in these changes was the arrival of the dingo (Australia’s wild dog), that possibly arrived from India (Gollan, 1985), the dispersal of the Australian Small Tool tradition (Glover & Presland, 1985), the appearance of technology that allowed plants to be processed (Beaton, 1977) and the expansion of the Pama-Nyungan language over most of Australia (Evans & Jones, 1997), Also, congruencies between the Pama-Nyungan and Dravidian languages were reported by Dixon (Dix, 1980). A study published by Hudjashov et al, (Hudjashov et al., 2007) used the improved resolution of the Y-chromosomal phylogeny to distinguish the Indian C-sub-haplogroup (C5) from the Australian C sub-haplogroups (C4a and C4b), which strongly suggested that no migrants from India reached Australia later than the original ‘Out of Africa’ migration. The authors did, in fact, argue that there has been no extensive genetic contact between the first settlers of Australia and other populations, and that it appears that Australia was largely isolated since the initial migration (Cavalli-Sforza, Menozzi & Piazza, 1994; Kirk & Thome, 1976; Nei & Roychoudhury, 1993). A recent study using short tandem repeats (STRs) has, however, observed significant affinity between the Arrernte people of Australia and populations from the Indian subcontinent (Alfonso-Sanchez, Perez-Miranda & Herrera, 2008). It is evident, therefore, that a clear picture is not provided by the available data of when and how many times anatomically modern humans arrived in Australia from India.

There have been several genetic studies (Basu et al., 2003; Cordaux et al., 2004; Bamshad et al., 2001; Sahoo et al., 2006; Sengupta et al., 2006) published that involved Indian populations but they failed to reach a consensus on the origins of the casts and tribes in India. It has been revealed by a recent genome-wide study (Beaton, 1977) that employed more than 500,000 SNPs, that modern Indian populations are a mixture of 2 source populations, the ancestral South Indians (ASI) and the ancestral North Indians (ANI). Tribal people are ideal candidates for genetic studies that seek to understand evolution of modern humans and their migrations, including the peopling of Australia, given that tribal people represent the original inhabitants of India (Basu et al., 2003; Thapar, 1996; Ray, 1973; Majumder, 2008). The Soliga are a tribal community in the Biligiri Rangana (BR) Hills, district of Chamarajanagar, southern state of Kamataka, India. The general physical description of the Soliga is consistent with that of the Australoid ethnic group: dark complexion, curly hair, short stature, dolichocephalic head, a sunken nasal root and a depressed nasal bridge (Chopra, 1965; Morab, 1977; Majumder, 1998). Their language is Soliganudi (Zaraska, 1997), a dialect that has 65% lexical similarity with Kannada, a Dravidian language that is spoken in Kamataka, Andhra Pradesh, Tamil Nadu and Maharashtra (Gordon, 2005). The Soliga tribe is the only scheduled tribe (ethnic minority group identified by the Indian Constitution for special consideration (Sujatha, 2002) in the BR Hills (Morab, 1977). They are considered among the ancient populations of India of the ‘Veddid’ type (Dravidian speaking, forest dwelling, tribes of South India), believed to be true autochthones (original inhabitants of a country) of India (Sarkar, 1954). The cultural, as well as geographic isolation of the Soligas from other populations (Morab, 1977) may be the result of their forest-bound way of life, together with the relative inaccessibility of the BR Hills.

Autosomal STRs are hypervariable markers that have proven to be of use in the elucidation of recent human evolution (Rowold & Herrera, 2003). The high resolution necessary for assessing phylogenetic relationships among human populations that are closely related is provided by the selective neutrality, widespread distributions throughout the genome, abundance, large numbers of alleles and high heterozygosity of autosomal STRs (Sarkar, 2003; Rowold & Herrera, 2003; Shepard et al., 2005; Shepard & Herrera, 2006a; Shepard & Herrera, 2006b). Unlike the uniparental mtDNA and Y-chromosome haplotypes, STRs and biparentally derived, which allows for a genetic profile of the population that is under scrutiny that is more representative.

There are 15 autosomal STR loci that were typed in the present study to characterise the genetic diversity of the Soliga people. The researchers then compared the allelic frequencies that were generated with other geographically targeted populations that had previously been published from India and other locations worldwide. Phylogenetic affinities between the Soliga and 2 Australian Aboriginal populations the Northern Territory were indicated by the data.

Interpopulation diversity

A CA, a NJ, dendrogram and the Carmody program’s G-test were used to ascertain phylogenetic relationships among all populations. Admixture analysis was used to examine genetic affinities and possible contributions to hybrid populations.

According to Morlote et al. there are 5 main aggregates that can be discerned within the CA plot: 1st of which consisted of all the populations of sub-Saharan Africa, with the exception of Madagascar, a 2^nd including Northeast and Southeast Asia, a 3^rd grouping all South Central Asians, with the exception of the Soligas. A rather tight cluster, with the exception of Rajbanshi, is formed by South Central Asia, which plots fairly close to the Northeast/Southeast Asia, and the Soliga tribe, which strays from the South Central Asian cluster to join the 2 Australian Aboriginal collections. The 2 southern Dravidian-speaking tribes, Kappu Naidu and Kamma Chaudhary, as expected, show more affinity to the Soligas than the other South Central Asian populations.

The CA graph corroborates the NJ phylogram in that 4 of the clusters in the CA are clearly represented. Well delineated clades in the tree are formed by the sub-Saharan African, Southwest Asian, Northeast and Southeast Asian populations. Confirming their association in the CA, the Soliga tribe again joins the 2 Australian populations. The populations from South Central Asia segregate between the clades from Northeast Asia and Southeast Asia that are in the lower half of the dendrogram whereas the Southwest Asia and the sub-Saharan Africa clusters partition in the upper half of the phylogram.

The group formed by the 2 Aboriginal Australian populations show the lowest Interpopulation variance value (Gst=0.00339); however, as only 2 Australian populations, that are both from the Northern Territory, were used in the study, it is not likely that the value reported in the study is representative of the actual Interpopulation variance of all Aboriginal Australian populations in the continent. The highest Gst (0.01474) is displayed by South Central Asia, with the exception of the all-populations group (Gst=0.02645). When the Soliga tribe is excluded from the South Central Asia group of populations the result is a 29.25 decrease in the Gst (0.01043). Upon the removal of the Soligas this considerable reduction in Gst argues for the genetic uniqueness of the tribe. According to Morlote it is noteworthy that when the Soligas were excluded, South Central Asia still has the highest Gst value for all the remaining geographic groupings, which indicates a high Interpopulation diversity is inherent to the region. Among the sub-Saharan African group (Ht= 0.80274) the total variance is at its highest, closely followed by the South Central Asian group, excluding the Soliga people (Ht=0.80059), and next is South Central Asia, with the Soliga people included (Ht=0.79910),

Genetic differences that are statistically significant were observed before the Bonferroni correction was applied (α=0.05) in the following pairwise comparisons: Kenya/Equatorial Guinea, Kenya/Angola, Qatar/Yemen and Iraq/Yemen. When the Bonferroni correction is applied for potential type I errors (α=0.0001149), several other pairwise comparisons were also proven to be statistically insignificant. It was found that the Soliga tribe differed significantly from all 29 populations it had been compared with. Prior to the Bonferroni correction statistically P-values are shown in bold italic whereas P-values that became insignificant after the Bonferroni correction was applied are shown in bold.

Proportions of admixture were calculated for Soligas by the use of 6 parental groups, which had been established based on geographic divisions and phylogenetic affiliations as was assessed in the CA and NJ analyses: sub-Shahan Africa, Southwest Asia, South Central Asia, Northeast Asia, Southwest Asia and Australia. The South Central Asian group exhibited a contribution of 70.5% to the Soligas. According to Morlote et al. it is significance that the only other group that show affinity for the Soliga genome is the from the Australian Aboriginal parental group, which shares 29.5% of its genetic material. When the 2 Australian groups were used as hybrids, south Central Asia was shown to be the major contributor to both Australian Aboriginals and the declared Australian Aboriginals (58.4 and 69.1%, respectively). Southwest Asia and sub-Saharan Africa are, interestingly, the second (23.9%) and 3^rd (13.4%) major contributors, respectively, whereas there is no contribution from Northeast Asia, sharing only 4.5% of its genetic material with the Aboriginal Australians and doesn’t contribute anything to the declared Aboriginal Australians.

Discussion

The tribal populations of India are considered to be the original inhabitants of the subcontinent. Morlote et al. suggest, therefore, that it is likely that many of the questions that have been unanswered about the evolution and migration of modern humans can be addressed by studying the indigenous people of India. Also, the coastal route out of Africa that was taken by modern humans that culminated in the initial settlement of Australia is believed to include migrational distance around the subcontinent of India, which would have provided ample opportunity for genetic signatures to be left behind. In this study Morlote et al. assessed the genetic profile of the Soligas, a tribe from southern India, based on 15 autosomal STR loci. They also explored the phylogenetic relationships of the tribe to other worldwide targeted populations.

The Soligas represent a genetic isolate in the BR Hills (Morab, 1977) that is part of the southern state of Karnataka, India. It is traditional for the Soliga to not interbreed with neighbouring populations like the Kappu Naidu and Kamma Chaudhary. Morlote et al. say there is no information as to why the Soligas reside in this mountainous region under conditions that are rather primitive. Yet, it is possible that as there is no gene flow, it is possible the Soligas have maintained a distinct gene pool. A number of population genetic parameters are a reflection of the genetic uniqueness of the Soliga people. One is their possession of the lowest number of alleles (115) of all the reference worldwide populations examined. They also display the lowest average heterozygosity that has been observed. The high degree of genetic homogeneity that was observed could also have been the result, in part, by the low status in the social hierarchy.

Conclusions

Both Australian Aboriginal populations from the Northern Territory and the Soligas share their 6 most abundant alleles, though not with any of the reference populations that were examined also suggest genetic affinities between the Soligas and the 2 Australian Aboriginal populations. Altogether, the data obtained by Morlote et al. portray the Soligas as a population with limited genetic diversity who exhibit unique genetic characteristics which set them apart from other populations from the Indian subcontinent. It appears to be indicated by a recent study (Hudjashov et al., 2007) that any similarities between Indian tribes and Australian Aboriginals result solely from genetic signals from the original ‘Out of Africa’ migration that might have taken place more than 70 ka, further enquiry into the possibility of more recent migrations from India to Australia is suggested by the genetic association between the Soligas and the 2 Australian Aboriginal populations in the Northern Territory observed in this study. Morlote et al. suggest that a future study that includes a larger number of tribal populations from Southern India, as well as additional Australian Aboriginal tribes that are defined better would be likely to shed more light on a possible connection between India and Australia that is more recent.

Sources & Further reading

Morlote, D. M., et al. (2011). "The Soliga, an isolated tribe from Southern India: genetic diversity and phylogenetic affinities." Journal Of Human Genetics 56: 258.