Monday, December 15, 2014

The Invasion That Never Was

Anand Rangarajan, here:

But it was the publication in 2011 of a path-breaking study that ultimately sealed the fate of the Aryan Invasion or Migration theory. Analysing 600,000 SNPs from as many as 30 ethnic groups – thereby extending the 2009 Nature ANI study through the inclusion of more European samples – Toomas Kivisild and co-workers discovered that both components of Indian ancestry, ANI and ASI, predate the Aryan Migration event by at least 9000 years. This was because the so-called k5 component, that bestows ancestry to South Asians, was found to contain no regional diversity differences; its spread across the Indian subcontinent must have happened well before 12,500 years ago (the detection limit) and not through a recent gene-flow event.

 In 2013 Singh and co-workers extended the Kivisild study with some acute observations, namely that the ANI and ASI populations mixed robustly between 1900 to 4200 years ago and that these two groups didn’t mix either before or after this window. The authors, by analysing genomes of 571 individuals representing 73 ethno-linguistic groups, also ruled out Eurasian gene flow during this time period, concurring with the finding of another study that such an event could not have happened before 12,500 years. Moreover, argued the scientists, 3500 years ago India was a already a densely populated region with well-established agricultural practices and therefore the Eurasian migration would have had to be immense in order to explain the fact that half the Indian population is derived from ANI.

The Aryan Migration event of 1500 BCE has also been questioned based on an authoritative haplogroup U linkage study wherein scientists found an extensive and deep late-Pleistocene link between Indians and Europeans, suggesting a coalescence near the time when Asia was initially being peopled. The migration that led to the Indo-Eurasian stock, according to these scientists, happened not 3,500 years ago but rather 12,500 years or earlier.

Another study, this time involving Y-DNA haplotyping, rules out substantial gene-flow from Europe to Asia at least since the mid-Holocene period, i.e. the last 6,500 years. It has also been shown that the gateway to the subcontinent, the Hindu Kush – where the earliest archaeological evidence of human remains dates back to 26,500 years before the Rig Veda – was a confluence of gene-flows in the early Neolithic period as opposed to an indigenous population.

There is one other way to corroborate that Eurasian migration happened much before the time-point vouched for by AMT proponents – skin colour. It has long been known that a single mutation, rs1426654, in the human pigmentation gene SLC24A5 accounts for the lighter skin tone of Europeans. A year ago, scientists discovered that an allele of the rs1426654 mutation was shared among many South Asian and Western Eurasian populations. The coalescence was calculated to be 22000-28000 years ago, with the frequency of occurrence of this mutation – called the allele frequency – found to be significantly higher in the ANI compared to the ASI.

The verdict of population genetics is clear, and profound, as pointed out subsequently by the lead author of the Nature study Dr Lalji Singh himself: “There is no genetic evidence that Indo-Aryans invaded or migrated to India. It is high time we re-write India’s prehistory based on scientific evidence.”