The scientists at the Centre for Cellular and Molecular Biology (CCMB), Hyderabad, in their study on human genetic diversity in tribals and caste populations across India, found path-breaking evidence that some Andamanese tribals are descendants of early Paleolithic colonizers of South-East Asia.

The DNA analysis study among these tribes, however, promises to result in far-reaching implications for the pharma and healthcare industry. The CCMB project, which aims at understanding the demographic history and genetic diversity for the mapping of complex genetic diseases in the sub-continent, is being done in collaboration with the Anthropological Society of India and an MoU has been signed by the institutions for the research.

CSIR and ICMR are supporting the programme, which had commenced with the research on the tribal populations in the Union Territory of Andaman & Nicobar Islands, according to Dr V R Rao, Deputy Director of Anthropological Survey of India.

Speaking to Pharmabiz.com, Dr Lalji Singh, director, CCMB, said that the DNA analysis of the primitive tribes of India might throw light on the very mystery of our own origins. It might even negate the out-of-Africa theory of human origin, which had been widely established.

The new findings are an outcome of the collaborative work among scientists of CCMB, the Anthropological Survey of India, Nagpur; the Regional Medical Research Centre, Port Blair, Andamans & Nicobar Islands; the Department of Genetics, Stanford University, USA; and the Department of Biology, University of Oslo, Norway.

As part of the study, the scientists analysed DNA from members of four present-day Andaman tribes and suggest that the islanders descended from early humans who migrated eastward out of Africa via Gujarat and Kerala during the last Ice Age, around 100,000 years ago.

Interestingly, some tribes in Gujarat and Kerala, which show close affinities to the Andamans Negrito tribes, are older than the Andamanese. Briefing newsmen about the new finding, Dr Lalji Singh, Director of CCMB, said these tribes in Gujarat and Kerala might have settled much before the Asian branch reached the sub-continent just before the last Ice Age. He said these two tribes in India were the oldest so far discovered genetically and might have landed from Africa in Gujarat, migrated to Kerala and then to Andamans.

The Andamanese tribes are one of the several isolated groups of small-statured hunter-gatherers, known as Negritos. In physical features, they resemble those of Africa with ebony black skin, peppercorn hair, scant body hair and large buttocks, making them a mirror image of the African Pygmies. Of the several linguistically distinct tribes, who populated the islands, only about half-a-dozen groups had survived - the Jarawas, the Great Andamanese, the Onges, the Sentinelese, the Shompenes and the Nicobarese. The present estimate indicates that the population of the Jawara tribe has been reduced to 200, the Great Andamanese to just 23 (14 males and 9 females), the Onges 98, the Sentinelese 250, the Shompenes 180 and the Nicobarese about 22,000.

Dr Lalji Singh and his fellow scientist Kumaraswamy Thankaraj, who undertook the first molecular study on the origin and genome combination of the vanishing tribals in Andamans, examined 68 blood samples belonging to four tribes. The findings titled " Genetic Affinities of the Andamans Islanders, a Vanishing Human Population" has been published online in " Current Biology" recently. The extraction and analysis of the hair DNA were performed by Erika Hagelberg at the ancient DNA Laboratory, University of Cambridge, UK. The genetic analysis of the DNA extracts from blood samples was conducted at CCMB laboratories.

The CCMB studies aimed at mainly two objectives, (1) to understand the mystery of our own origins and to understand the origin and history of the people of India and (2) to understand the genetic basis of complex diseases. To better understand the genetic basis of complex genetic diseases, in both tribals and non-tribals, it was important to study genetic diversity in tribal populations. Such studies will be all the more important if common diseases turn out to be caused by common susceptibility alleles that are likely to be old and, therefore, present in tribal populations. Many of the environmental risk-factors that may be responsible for triggering certain complex diseases may not be common in tribals. In such cases, it would be more feasible to differentiate genetic factors from environmental risk-factors for these diseases. As environmental risk-factors are known to be associated and are prevalent with urban and more sedentary lifestyles it becomes imperative to study the genetic diversity among Indian tribal populations, particularly the primitive ones.

Based on the various evidences available from the past, there are three models of human evolution, which have emerged out of the efforts of various research workers in the field, namely the Multi-regional model, the Recent African Origin (RAO) model and the Assimilation (or Hybridisation) model. According to the Multi-regional model, there was no single geographical origin for modern humans, but that after the radiation of Homo erectus from Africa into Europe and Asia some millions of years ago, there were independent transitions in regional populations from Homo erectus to Homo sapiens. Simultaneous evolution from Homo erectus to Homo sapiens in dispersed populations could have been achieved through extensive gene flow among geographically diverse populations.

According to the RAO model all non-African populations descend from a Homo sapiens ancestor that evolved in Africa 100,000 -200,00 years before present (yrBP). These ancestors then spread throughout the world, replacing archaic Homo-populations (for example the Neanderthals). This model is supported by fossil records, as the earliest modern human fossils were found in Africa and the Middle East, dating 90,000 - 120,000 yrBP. The recent genetic evidences at present support this model. The RAO model predicts that all genetic lineages derive from a recent common African ancestor and that non-African populations should carry a sub-set of the genetic variations present in modern African populations.

The Assimilation model proposes some gene flow between modern humans who migrated from Africa and archaic populations (for example Neanderthals) outside Africa. So the evolution of modern humans could have been due to a blending of modern characters derived from African populations with local characteristics in archaic European populations. The present finding supports the 'out-of-Africa' theory.

The CCMB study is the first molecular genetic evidence on the affinities of the Andaman Islanders, arguably the most enigmatic people on our planet. Mitochondria is the power house of every cell of our body. However, the Mitochondrial DNA (mtDNA) is a genetic element passed down only through women. This shows that the Jarawas and the Onges belong to the M lineage that is common throughout Asia. This establishes them as Asians and not Africans. The researchers also studied the DNA of Y-Chromosome, which is passed down to next generations only through men. The Jawara and Onge men turned out to carry a special change or mutation in the DNA of their Y-Chromosome. This is indicative of the Paleolithic population of Asia, the hunter-gatherers who preceded the first human settlements.

While the Andamanese are the descendants of the Paleolithic people, the Nicobarese have genetic affinities to groups widely distributed today throughout Asia. Thus the Nicobarese should presumably descend from the Neolithic agriculturists.