Too early to settle the Aryan migration debate?: 

Too early to settle the Aryan migration debate?: 

Context:

• With genetic data currently available, it is difficult to deduce the direction of Aryan migration either into India or out of India during 3200 BC.

Introduction:

• Scientists are converging the Aryan migration to the Subcontinent around 2000-1500 BC.
• Anyone who understands the complexity of Indian population will appreciate that Indians living outside the Subcontinent do not reflect the full diversity of India, as the majority of them are from caste populations with limited subset of regions.
• India is home to 4,700 ethnic populations, including socially stratified communities, many of which have maintained endogamy (marrying within the community) for thousands of years, and these have been hardly sampled in the Y chromosome analysis and so do not provide an accurate characterization of the R1a frequencies in India (several tribal populations carry substantial frequency of haplogroup R1a).
• Equally important to understand is that the Y chromosome phylogeny suffered genetic drift (lineage loss), and thus there is a greater chance to lose less frequent R1a branches, if one concentrates only on specific populations, keeping in mind the high level of endogamy of the Subcontinent.
• These are extremely important factors one should consider before making any strong conclusions related to Indian populations.

Genetic affinities:

• The split with the European is around 6,000 years and thereafter the Asian branch (Z93) gave rise to the South Asian (L657), which is a brother branch of lineages present in West Asia, Europe and Central Asia.
• Scientists using more than 5, 00,000 autosomal genetic markers, showed that the Ancestral North Indians (ANI) share genetic affinities with Europeans, Caucasians and West Asians.
• Another study holds the opinion that when the Gujarati Indians in Houston (GIH) were analysed for genetic affinities with different ethnic populations of India, it was found that the GIH have formed two clusters in Principal Component Analysis (PCA), one with Indian populations, another an independent cluster.
• Another study analysed 74 patients with neuromuscular diseases (of mitochondrial origin) living in the U.K. and found a mutation in RNASEH1 gene in three families of Indian origin.
• However, this mutation was absent in Indian patients with neuromuscular diseases (of mitochondrial origin).
• This mutation was earlier reported in Europeans, suggesting that these three families might have mixed with the local Europeans.
• Yet another study analysed 142 samples from 30 ethnic groups and mentioned that modeling of the observed haplotype diversities suggests that both Indian ancestry components (ANI and ASI) are older than the purported Indo-Aryan invasion 3,500 YBP (years before present).
• As well as, consistent with the results of pairwise genetic distances among world regions, Indians share more ancestry signals with West than with East Eurasians.

Conclusion:

• The findings could be biased and confusing is at all one doesn’t understand the complexity of the Indian populations and select samples carefully for analysis. For example:
• Tribes are one of the founding populations of India, any conclusion drawn without studying them will fail to capture the complete genetic information of the Subcontinent.