Historians have always struggled with the conjectural nature of Ancient Indian dates. We know the Buddha was a rough contemporary of Confucius, Mahavira and Lao Tze in the fifth-sixth century BCE. We know Alexander invaded India in 326 BCE. We don' know much about what happened in-between, or before, or after.
It is difficult to establish timelines and concrete historicity for any ancient Indian event. Did the Aryans come to India out of Central Asia, or were they indigenous? When were the Vedas composed? Ditto for the Ramayana and Mahabharata? The epics post-date the Vedas and the Mahabharata is post-Ramayana but that is all we can say with certainty.
Some questions related to caste are also ideologically loaded. When did society become caste-based and how long did it take before endogamy - the custom of marrying inside caste - become prevalent? The Vedas make no references to caste whereas the two epics have many. Both the Manusmriti and the Arthashastra speak with approval of the caste system.
Data from a couple of genetic studies could add grist to the speculative mill, apart from being of great medical significance. A paper in the American Journal of Human Genetics, titled Genetic Evidence for Recent Population Mixture in India offers details of a study conducted by a joint group from Harvard, MIT, and the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad. This is a follow-up to an earlier study by the same group, published in Nature in 2009.
The 2009 study was comprehensive. It examined 500,000 genetic markers in the genomes of 132 individuals from 25 groups, across 13 states and all six Indian language families, including upper and lower castes, and tribal groups. The 2013 study extended this, sampling 571 individuals from 73 "ethno-linguistic" groups. The researchers developed a new statistical tool-kit to analyse this data.
The 2009 study claimed ancient India had two major genetic groups, named the ancestral north Indians (ANI) and the ancestral south Indians (ASI). The ANI are related to Central Asians, Middle Easterners, Caucasians, and Europeans. The ASI are not closely related to groups outside the subcontinent.
Modern Indians have a mixture of ANI and ASI genes, with the exception of the Andaman Islanders, who are exclusively ASI. Although the genome sequences of two unrelated individuals differ by only about 0.1 per cent, that difference provides clues about origins. Genetic markers that heighten the risk of certain diseases can also be located.
ANI and ASI had distinctive chromosomes. When ANI and ASI populations originally mixed, chromosomal segments from each group would have been long. The recombination of maternal and paternal genes would have broken up these segments per chromosome, per generation. By measuring lengths of chromosomes segments in genomes, the study can infer that ANI-ASI mixtures occurred continuously from about 4,200 years ago to about 1,900 years ago. Northern groups have more recent dates and southern groups, older dates. This may be because the northern groups have multiple mixtures due to waves of new emigrations.
The study notes that the period between 4,200 years ago and 1,900 years ago, "was a time of profound change, characterised by the de-urbanisation of the Indus civilisation, increasing population density in the Gangetic system, and the likely appearance of Indo-European languages and Vedic religion."
The finding that nearly all Indian groups descend from ANI-ASI mixes also applies to tribes and castes. Kumarasamy Thangaraj, a co-author from CCMB, says, "It is impossible to distinguish castes from tribes. They are not systematically genetically different."
About 1,900 years ago, genetic pools froze in place, probably due to endogamy becoming widespread. Thangaraj deduces that "The high incidence of genetic and population-specific diseases that is characteristic of present-day India is likely to have increased only when groups started following strict endogamous marriage".
Another finding that is somewhat surprising has important medical implications. Many groups in modern India descend from a small number of founding individuals, and these have remained genetically isolated from other groups. In genetic parlance, this is a "founder event."
Founder events, in groups such as the Finns and Ashkenazi Jews, are known to increase the risk of certain recessive genetic diseases. It's probable the same holds true here. It would explain why the incidence of genetic conditions such as diabetes and heart disease is greater among certain Indians. A systematic survey to identify strong founder events could pinpoint the genes responsible for such diseases, and identify people with specific risks.
The studies provide partial illumination to some historical questions. If caste-based endogamy became entrenched about 1,900 years ago, it was well after it was approved of in the epics, and the Manusmriti. Caste structure was also described by Megasthenes in his Indica circa 300 BCE, and the contemporaneous Arthashastra. So, castes and tribes did intermarry for many centuries.
Another interesting point is that the ANI-ASI divide suggests these populations did not mingle before 2,100 BCE or thereabouts. The ANI's genetic links to external groups, versus the ASI's lack of such links, provides support for the thesis of an Aryan migration into India around 2,100 BCE. Or perhaps, ANI and ASI lived isolated from each other before that period and the ANI migrated out to Central Asia and beyond? Another study, that used similar methods to compare ANI genetic material to that of Central Asian groups, may provide more definitive evidence either way.
The medical implications are obviously of more immediate importance and those suggest that caste-based endogamy has ill-effects. Also studies like this also open up the fascinating possibility that genetic studies could aid considerably in a reassessment of the social and historical origins of Indians.
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