DNA-BASED EVIDENCES FOR EARLY MIGRATIONS INTO INDIA

The study of where human beings originated and how they spread across the world has been transformed in recent years. The big new jump in scientific knowledge was made possible by a new method of acquiring facts - that of examining people's DNA, instead of relying on the study of fossils alone. Among the surprising new conclusions being drawn is that the first human beings to come into India, came not through the cold passes of the Himalayas, but along the warm, green coastline of the Indian ocean. Of course they hadn't thought they were coming into a country called India – they were just simple people moving onwards in search of food and water, sometimes seeking to escape someone they did not like, sometimes in search of new friends.

The basis of the new techniques, which have led to remarkable new conclusions, is what has been called the “molecular clock”. It seems that there seems to exist a sort of a “molecular clock” in all of us, which keeps ticking away with the passage of time. Thus, the DNA in our bodies will keep gradually changing as time goes by. What's new about that, you may say – everybody knows that our DNA is different in each generation, the product of an inter-mixing of our parents' respective DNA. But even after you discount the effects of the exchange of DNA between parents, there still takes place a slow, gradual process of DNA change. This is due to random mutations. As a result, if a group of people splits into two sub-groups which went off in different directions and got separated from each other for thousands of years, they will gradually develop a slight underlying pattern of differences in their DNA. By comparing these underlying differences, we can get an estimate of how long ago it was that these two sub-groups had separated.

Such a method has proved extremely useful in finding who are our closest relatives and what routes we may have migrated from. The DNA to be found in our mitochondria and in Y chromosomes are especially suitable for such studies. Mitochondria are small bodies found in all cells and are responsible for making energy available for the cell's functions. They have their own DNA which permit them to replicate on their own. During fertilization in humans, the DNA of the sperm fuses with the maternal DNA, and the nuclear DNA of the fertilized egg is a mixture of the two parents' DNA. However, the fertilized egg inherits mitochondria only from the mother. The father's mitochondra, significantly, never enter the fertilized egg to confuse the DNA patterns of the mother's mitochondra. In other words, our mitochondrial DNA forms an unbroken line from our mother, to her mother and to her mother right up to the origin of this human species. This means that if want to understand the differences between people it is much simpler to study mitochondrial DNA than to try and tease apart the complex mosaic formed by the intermixing of nuclear DNA in every generation. For similar reasons, Y chromosomes which are contributed only by the father to the son are also favoured for study.

The comparisons of the molecular clocks in different human groups tells us which groups are more closely related and which are more distantly related. The differences between two sets of mitochondrial DNA can tell us how long ago was it that these two populations separated from each other. A large number of such studies, thus tell us that all modern human beings split off from a common group of ancestors at the most around 200,000 years ago. The differences in DNA are such that they seem to radiate outward from certain African groups. This tells us that the earliest modern humans most probably lived in Africa and it is from there that they have spread to occupy the rest of the world.

A recent study published in the journal Science reports the analysis of data which indicate that the migrations from Africa out along the coast of Africa and made their way to the north and east along the coast of what is now the Middle East. From here around 60000 to 75000 years ago one off-shoot seems to have moved into Europe and another moved further east, along the coast of India. The path of the movement seems to have been along the coast, rather than through the inland, mountain passes taken by later immigrants. This movement into India was quite rapid and going down the coast of what we now call the Arabian sea, seems to have moved up along our Bay of Bengal into south-east Asia. From there offshoots went to China in the north and Australia to the south.

It is along this path that we find several peoples who seem to be “relicts” of that earliest migration, subsequently isolated and surrounded by the later migrations into these lands. The mitochondrial DNA and Y chromosomes of these “relicts” show many common features across groups as disparate now as some of the aboriginal tribals of southern India, the aboriginal people of Malaysia and the bushmen of Australia. While similar amongst themselves, they are quite distinct from the surrounding and now much more populous non-aboriginal communities. The best explanation of this seems that these aboroginal peoples are those remnants of that first wave, who stayed isolated for a variety of reasons that led to their not having cross-bred with later immigrants.

This corroborates well with several other studies, like that published in the journal Genome Research in 2003. This analysed the mitochondrial DNA of 44 different ethnic groups in India. The results indicated that the ancestors of the Austro-Asiatic tribals like the Ho, the Munda and the Santals were the earliest to enter this land. The Dravidic speaking tribals like the Gond, Irula and the Kurumba seem to have forked off later. Large influxes of people have also come into India from the north-east. They seem to have closer links to the people who were the early immigrants into China, turning later down south to enter India from the east.

This study also indicates that the upper castes of both North and South India have much closer affinities with central Asian populations. The lower castes seem to be earlier entrants and the upper castes later entrants into their regions. The upper castes of North India, however, seem to have come in much later than those of South India. The differences between castes is much more sharp in the south than in the north.

The results of DNA-based dating are at the frontiers of contemporary science. The statistical methods and the lab techniques being used are quite complicated and are still being carefully examined and cross-checked by other scientists. Several kinds of questions remain unanswered and some improvements in techniques are also being suggested. Yet, it does seem that these new methods will go a long way in helping us to fit together a realistic picture of how humans spread out across the world from Africa. The mosaic of people that is today's India is a long history of successive migrations, sometimes making peace with other groups, sometimes making war, sometimes settling in domination of others, sometimes simply moving further away to live in peace. The human adventure is truly a complex one.