Last week was a good one for all those who had been waiting endlessly for the Rakhigarhi aDNA paper to see the light of day and also for the pre-print ‘The Genomic Formation of South & Central Asia’ to come out in a peer-reviewed journal.
Unfortunately, the talk around both these papers has quickly degenerated to only figuring out whether these papers support an Aryan Migration or whether they do not.
However, the combined data that has come out from these two papers is a treasure trove of information and this data has enormous implications for a lot of other theories of South Asian prehistory.
I wish to focus one post for each of these important discoveries starting with the important discovery about the antiquity of IVC ancestral population in South Asia and its implication for origins of farming in the region.
The graphical extract given above is quite self-explanatory. But let us also quote from the paper itself to re-inforce what the graphical extract implies :-
The Iranian-related ancestry in the IVC derives from a lineage leading to early Iranian farmers, herders, and hunter gatherers before their ancestors separated, contradicting the hypothesis that the shared ancestry between early Iranians and South Asians reﬂects a large-scale spread of western Iranian farmers east. Instead, sampled ancient genomes from the Iranian plateau and IVC descend from different groups of hunter-gatherers who began farming without being connected by substantial movement of people.
They elaborate on what the implications of this finding is –
Our evidence that the Iranian-related ancestry in the IVC Cline diverged from lineages leading to ancient Iranian hunter-gatherers, herders, and farmers prior to their ancestors’ separation places constraints on the spread of Iranian-related ancestry across the combined region of the Iranian plateau and South Asia, where it is represented in all ancient and modern genomic data sampled to date. The Belt Cave individual dates to 10,000 BCE, deﬁnitively before the advent of farming anywhere in Iran, which implies that the split leading to the Iranian-related component in the IVC Cline predates the advent of farming there as well…Thus, the Iranian-related ancestry in the IVC Cline descends from a different group of hunter-gatherers from the ancestors of the earliest known farmers or herders in the western Iranian plateau.
So the paper on the Rakhigarhi aDNA sample makes it abundantly clear that the geneticists find the Iran farmer/herder related ancestry in the IVC people to have split up from the actual Iranian farmers/herders atleast before 12,000 years ago. This is well before the origin of farming on the Iranian plateau. Therefore, the clear implication of this is that the Iranian Neolithic Farmers did not contribute ancestry to the ancestors of the Harappans but that the ancestors of Harappans and the early Iranian farmers/herders descend from a common ancestral source that existed more than 12 kya.
What was the place of origin of that ancestral source ? We do not know that as yet so to assume that it is coming from Iran, as some are doing, is not borne out by evidence. It may well have originated in South Asia before moving into Iran.
I have written at length on this topic at my blog.
Infact, the deep pre-Neolithic origins of Iran N like ancestry in South Asians was already becoming apparent that as early as 2011 when this major paper on South Asian populations made the following observation –
… regardless of where this component was from (the Caucasus, Near East, Indus Valley, or Central Asia), its spread to other regions must have occurred well before our detection limits at 12,500 years.
Even before this, in 2004, when a paper, by this very same Estonian team, on mtDNA lineages shared between Iran & South Asia had come out, it was already noted that the spread of shard mtDNA lineages between the two regions was quite old.
This separation between the South Asian & Iranian farmer/herder ancestry not just dates to before 12 kya but it likely dates to the very end of the Last Glacial Maximum, somewhere around 18-17 kya.
The above graphic shows the early split of mtDNA U7 across Eurasia. One can quite clearly see that the oldest splits seem to be between Iranian plateau & South Asia. This pattern is also observable for other shared mtDNA & y-dna lineages shared between these 2 regions. For more on this please refer to my blog.
Therefore, the Rakhigarhi provides one more line of evidence to re-inforce what was already evident from many previous studies on modern DNA, that the major portion of the shared ancestry between the Iranian plateau and South Asia was not brought into South Asia from Iran by the Iranian farmers but had separated from the ancestors of Iranian farmers/herders well before 12,000 years ago. With this Rakhigarhi paper getting such widespread coverage, one can only hope that from now on this fact will become known to much more people than it had been previously.
South Asian Neolithic
Since it has now become clear that there was no migration of early Iranian farmers into South Asia, so it has begun to be argued that farming must have been adopted by local NW hunter gatherers of South Asia through spread of ldeas from the fertile crescent.
While this is certainly plausible, it rests on the premise that farming began independently only once in the Fertile Crescent and it spread from there to everywhere else.
This is however not so straightforward. There are similarities at Mehrgarh with the Neolithic sites of the Eastern Fertile Crescent or the Iranian Neolithic but not with the Levant or Anatolian Neolithic. The archaeologist who discovered the Neolithic site of Mehrgarh and carried out decades of excavation over there, J F Jarrige, had this to say
The similarities noticed between Neolithic sites from the eastern border of Mesopotamia to the western margins of the Indus valley are highly significant. A sort of cultural continuum between sites sharing a rather similar geographical context marked with an also rather similar pattern of evolution and transformation becomes more and more evident. But the Neolithic of Mehrgarh displays enough original features to imply an earlier local background which has so far not been documented. Nevertheless the cultural dynamism shown by the inhabitants of Mehrgarh as early as level I of Period I indicate that the Neolithic of Balochistan cannot be interpreted as the “”backwater” of the Neolithic culture of the Near East. (link)
So indeed there are cultural similarities between the South Asian Neolithic and the West Iranian Neolithic and we know that the early farmers of both these regions were also separated from a common ancestor but the genetic evidence makes it clear that the common ancestor likely lived at the end of LGM aroynd 18 kya rather than the beginning of Neolithic around 9-8 kya.
It is not quite clear how the early South Asian & Iranian farmers interact or relate to each other during this Neolithic phase but it is quite clear that the early Iranian farmer was significantly different than the nearby farmers of the Levant & Anatolia both genetically and even culturally while he has much more in common with his much distant eastern cousins. Might not this imply that the origins of these Iranian farmers lay to the east close to its South Asian cousins ?
Jarrige provides several lines of evidence that suggest that the Neolithic in South Asia developed independently of West Asian input.
Lorenzo Costantini has shown that the plant assemblage of Period I is dominated by naked six row barley which accounts for more than 90% of the so far recorded seeds and imprints. He has also pointed out the sphaerococcoid form of the naked-barley grains with a short compact spike with shortened internodes and small rounded seeds. According to him, such characteristics in the aceramic Neolithic levels can be ascribed to probably cultivated but perhaps not fully domesticated plants. Domestic hulled six-row barley (H. vulgare, subsp. vulgare) and wild and domestic hulled two-row barley (H. vulgare subsp. spontaneum and H. vulgare subsp. distichum) have also been recorded, but in much smaller quantities. According to Zohary quoted by R.H. Meadow, the distribution of wild barley extends today to the head of the Bolan Pass. It is therefore likely that local wild barleys could have been brought under cultivation in the Mehrgarh area.
The main crop at Mehrgarh was barley by far and we see that there is enough evidence to suggest its local domestication from nearby wild varieties.
There is also genetic evidence to suggest two independent centers of barley domestication.
There has long been speculation that barley was domesticated more than once. We use differences in haplotype frequency among geographic regions at multiple loci to infer at least two domestications of barley; one within the Fertile Crescent and a second 1,500–3,000 km farther east. The Fertile Crescent domestication contributed the majority of diversity in European and American cultivars, whereas the second domestication contributed most of the diversity in barley from Central Asia to the Far East.
It is abundantly clear that the barley used by South Asian Neolithic farmers fits in very well with this second domestication scenario.
Jarrige also notes,
The presence of bones of relatively small subadult and adult animals in the trash deposits of the early levels confirms, according to R.H. Meadow, the domestic status of at least some of the goats. Meadow has also clearly shown that “” though in the course of Period I at Mehrgarh, the remains of sheep and cattle became to increasingly dominate the faunal assemblages of the successive strata, at the same time, the animal represented grew smaller in body size”. By the end of Period I, cattle bones amount for over 50% of the faunal remains. Osteological studies as well as clay figurines indicate that zebu cattle (Bos indicus) is well attested in Period I and became most probably the dominant form (Fig. 12). Mehrgarh provides us therefore with a clear evidence of an indigenous domestication of the South Asian zebu. We know today that Bos indicus and Bos Taurus, the non-humped bull from the Middle-East, have a different genetic origin. Therefore the assumption that farming economy was introduced full-fledged from Near-East to South Asia needs to be questioned.
The archaeological & genetic evidence therefore clearly implies a local domestication of indigenous cattle just as is the case with the domestication of barley. Even the goats and sheep were likely domesticated from local wild populations of the same. We may bear in mind that the Iranian Neolithic farmers were essentially goat herders and did not have cattle for a long period before it eventually came in from the Anatolian-Levant region. So they couldn’t possibly bring in the know-how or cattle domestication to South Asia.
With such an abundance of evidence at our disposal it becomes clear that the origins of Neolithic economy in South Asia can be attributed to local South Asian Hunter Gatherers, deeply related to Iranian farmers/herders, who started it by indigenous domestication of barley and cattle from local wild ancestors. So the only question that remains is whether the Neolithic technological knowledge came in from the Fertile Crescent.
That is difficult to answer, but we may end here by noting that in the case of the Near Eastern Neolithic, the transition from hunting gathering phase to the farming phase brought about an admixture of Iranian Farmer like admixture in the local Anatolian HGs.
In the above figure a, AHG is Anatolian HG while AAF is Anatolian Aceramic Farmer. We see from this graphic that, with a transition from AHG to AAF, we see that there is an influx of admixture into AAF which brings it slightly closer to Iranian Farmer & CHG ancestry. In contrast no such admixture is seen in South Asian farmers.
So might this indicate that the Neolithic technology spread from East to West ? Future research will surely shed more light on it but it should be clear to everyone that South Asia most likely was an independent and major center of Neolithic transition and deriving its origin from the Fertile Crescent looks rather unconvincing.
We may also look afresh at the question of origins of Central Asian Neolithic and whether it derived from Iranian Neolithic or South Asian Neolithic.