(Weekly Organ of the Communist Party of India (Marxist)
October 18, 2009
A RECENT study by scientists
from the Centre for
Cellular and Molecular Biology (CCMB) and Harvard has come out with a
findings about the nature of the ancestral Indian population. The study -- Reconstructing Indian population history
(Nature, 24 September 2009 | doi:10.1038/nature08365) -- is not a sharp
with the past as some of the newspaper reports have reported but very
line with past studies. Roughly, the study shows that the Indian
an admixture of an Ancient South Indian (ASI) and a slightly younger
North Indian (ANI) population. The proportion of the two varies,
south to north, with the North Indian population being closer to the
Another interesting find in the
study is that the Onge
group in Andaman, who number today in only a few hundreds, is much more
related to the ASI population and must have broken off before the ANI
population appears in
The major difference of this study with the earlier ones is the amount of data they used in the study. While the other studies had looked at only a few genetic markers in the samples of the people they had taken, this study uses a much higher number of markers.
How do we study genetic variations in a population? Some of the genes in our DNA sequence have multiple forms that they exist in and the alternate forms are called alleles. This means that within the human genetic sequence, there are different expressions of the genes that produce differences within the population. For example, one form of this gene (or allele) produces brown eyes, the other green. A gene is a DNA sequence within the genome and each Nucleotide is a specific location within this DNA sequence. If the DNA sequence is looked on as a ladder, each location is like a rung coded from its basic building blocks in this DNA ladder. If a nucleotide has only two forms -- there is a single mutation in a nucleotide -- we call these single nucleotide polymorphisms (SNPs). The variation of the SNPs in a population is a measure of the genetic diversity of the population.
Most of these different versions of the nucleotides do not lead to any difference in the people – these differences are neutral. The SNPs that display functional differences are only about 1per cent of the total 10 million SNPs that exist in the human population. Although the DNA sequences of any two unrelated people differ by only a small amount – less than 0.1per cent -- this small amount of genetic material can provide insights into ancient migrations and origins of the current populations.
The current study differs from the earlier ones in the amount of data that they have used. They have looked at 560,000 SNPs in the Indian population. Though their SNP numbers were very large, the sample size of groups and people chosen were not high. They took only 132 individuals from 25 groups in 13 states. The earlier studies had looked at much smaller number of SNPs and therefore the fact that even with a much larger number of SNPs, the same results have been reached is a vindication of the power of genetics in unravelling some of these questions.
Though they have been careful
not to suggest that the
genetic studies tell us anything about language – Indo European or
the data seems to suggest that there is more of an influx from the
of India to
The press reports of this study have been quite mixed. Some have claimed that the genetic studies show there is no difference between South Indians and North Indians. Some have also claimed that the Aryan Dravidian divide is a myth. The study clearly shows that while the ANI and ASI population are present in almost all the Indian population groups, the proportions are different. The more north we go, the proportion of ANI rises, while the more south we go, the more it falls. The Indian Palaeolithic population consisted of first the ASI, which settled at least 65,000-70,000 years ago. The second group, the ANI came around 40,000-50,000 years ago. The Onge is a part of the ASI population and branched off from the ASI about 40,000 to 50,000 years ago and show no ANI markers.
Different groups in
The small founding population and inbreeding populations have some medical implications. Each of the groups have a larger share of what are called recessive genes and this would show up in a higher prevalence of genetic diseases based on recessive genes.
As we have written earlier, no serious historian today posits a huge influx of Indo Aryan speaking people replacing the original population in the north. The spreading of language can take place through dominance of a group, conquering the rest and becoming the new elite. This squares well with what the genetic record now tells us and is very much in line with what historians such as Iravati Karve, DD Kosambi and Romila Thapar have maintained. It is also in line with the linguistic evidence that we have.
There has been a relative
scarcity of such studies for
the Indian population.