The thorniest, most fought-over question in Indian history is slowly
but surely getting answered: did Indo-European language speakers, who
called themselves Aryans, stream into India sometime around 2,000 BC –
1,500 BC when the Indus Valley civilisation came to an end, bringing
with them Sanskrit and a distinctive set of cultural practices? Genetic
research based on an avalanche of new DNA evidence is making scientists
around the world converge on an unambiguous answer: yes, they did.
This may come as a surprise to many — and a shock to some — because the dominant narrative in recent years has been that genetics research
had thoroughly disproved the Aryan migration theory. This
interpretation was always a bit of a stretch as anyone who read the
nuanced scientific papers in the original knew. But now it has broken
apart altogether under a flood of new data on Y-chromosomes (or
chromosomes that are transmitted through the male parental line, from
father to son).
Lines of descent
Until recently,
only data on mtDNA (or matrilineal DNA, transmitted only from mother to
daughter) were available and that seemed to suggest there was little
external infusion into the Indian gene pool over the last 12,500 years
or so. New Y-DNA data has turned that conclusion upside down, with
strong evidence of external infusion of genes into the Indian male
lineage during the period in question.
The reason for the
difference in mtDNA and Y-DNA data is obvious in hindsight: there was
strong sex bias in Bronze Age migrations. In other words, those who
migrated were predominantly male and, therefore, those gene flows do not
really show up in the mtDNA data. On the other hand, they do show up in
the Y-DNA data: specifically, about 17.5% of Indian male lineage has
been found to belong to haplogroup R1a (haplogroups identify a single
line of descent), which is today spread across Central Asia, Europe and
South Asia. Pontic-Caspian Steppe is seen as the region from where R1a
spread both west and east, splitting into different sub-branches along
the way.
The paper that put all of the recent discoveries together
into a tight and coherent history of migrations into India was
published just three months ago in a peer-reviewed journal called ‘BMC
Evolutionary Biology’. In that paper, titled “A Genetic Chronology for
the Indian Subcontinent Points to Heavily Sex-biased Dispersals”, 16
scientists led by Prof. Martin P. Richards of the University of
Huddersfield, U.K., concluded: “Genetic influx from Central Asia in the
Bronze Age was strongly male-driven, consistent with the patriarchal,
patrilocal and patrilineal social structure attributed to the inferred
pastoralist early Indo-European society. This was part of a much wider
process of Indo-European expansion, with an ultimate source in the
Pontic-Caspian region, which carried closely related Y-chromosome
lineages… across a vast swathe of Eurasia between 5,000 and 3,500 years
ago”.
In an email exchange, Prof. Richards said the prevalence of
R1a in India was “very powerful evidence for a substantial Bronze Age
migration from central Asia that most likely brought Indo-European
speakers to India.” The robust conclusions of Professor Richards and his
team rest on their own substantive research as well as a vast trove of
new data and findings that have become available in recent years,
through the work of genetic scientists around the world.
Peter
Underhill, scientist at the Department of Genetics at the Stanford
University School of Medicine, is one of those at the centre of the
action. Three years ago, a team of 32 scientists he led published a
massive study mapping the distribution and linkages of R1a. It used a
panel of 16,244 male subjects from 126 populations across Eurasia. Dr.
Underhill’s research found that R1a had two sub-haplogroups, one found
primarily in Europe and the other confined to Central and South Asia.
Ninety-six per cent of the R1a samples in Europe belonged to
sub-haplogroup Z282, while 98.4% of the Central and South Asian R1a
lineages belonged to sub-haplogroup Z93. The two groups diverged from
each other only about 5,800 years ago. Dr. Underhill’s research showed
that within the Z93 that is predominant in India, there is a further
splintering into multiple branches. The paper found this “star-like
branching” indicative of rapid growth and dispersal. So if you want to
know the approximate period when Indo-European language speakers came
and rapidly spread across India, you need to discover the date when Z93
splintered into its own various subgroups or lineages. We will come back
to this later.
So in a nutshell: R1a is distributed all over
Europe, Central Asia and South Asia; its sub-group Z282 is distributed
only in Europe while another subgroup Z93 is distributed only in parts
of Central Asia and South Asia; and three major subgroups of Z93 are
distributed only in India, Pakistan, Afghanistan and the Himalayas. This
clear picture of the distribution of R1a has finally put paid to an
earlier hypothesis that this haplogroup perhaps originated in India and
then spread outwards. This hypothesis was based on the erroneous
assumption that R1a lineages in India had huge diversity compared to
other regions, which could be indicative of its origin here. As Prof.
Richards puts it, “the idea that R1a is very diverse in India, which was
largely based on fuzzy microsatellite data, has been laid to rest”
thanks to the arrival of large numbers of genomic Y-chromosome data.
Gene-dating the migration
Now
that we know that there WAS indeed a significant inflow of genes from
Central Asia into India in the Bronze Age, can we get a better fix on
the timing, especially the splintering of Z93 into its own sub-lineages?
Yes, we can; the research paper that answers this question was
published just last year, in April 2016, titled: “Punctuated bursts in
human male demography inferred from 1,244 worldwide Y-chromosome
sequences.” This paper, which looked at major expansions of Y-DNA
haplogroups within five continental populations, was lead-authored by
David Poznik of the Stanford University, with Dr. Underhill as one of
the 42 co-authors. The study found “the most striking expansions within
Z93 occurring approximately 4,000 to 4,500 years ago”. This is
remarkable, because roughly 4,000 years ago is when the Indus Valley
civilization began falling apart. (There is no evidence so far,
archaeologically or otherwise, to suggest that one caused the other; it
is quite possible that the two events happened to coincide.)
The
avalanche of new data has been so overwhelming that many scientists who
were either sceptical or neutral about significant Bronze Age migrations
into India have changed their opinions. Dr. Underhill himself is one of
them. In a 2010 paper, for example, he had written that there was
evidence “against substantial patrilineal gene flow from East Europe to
Asia, including to India” in the last five or six millennia. Today, Dr.
Underhill says there is no comparison between the kind of data available
in 2010 and now. “Then, it was like looking into a darkened room from
the outside through a keyhole with a little torch in hand; you could see
some corners but not all, and not the whole picture. With whole genome
sequencing, we can now see nearly the entire room, in clearer light.”
Dr.
Underhill is not the only one whose older work has been used to argue
against Bronze Age migrations by Indo-European language speakers into
India. David Reich, geneticist and professor in the Department of
Genetics at the Harvard Medical School, is another one, even though he
was very cautious in his older papers. The best example is a study
lead-authored by Reich in 2009, titled “Reconstructing Indian Population
History” and published in Nature. This study used the
theoretical construct of “Ancestral North Indians” (ANI) and “Ancestral
South Indians” (ASI) to discover the genetic substructure of the Indian
population. The study proved that ANI are “genetically close to Middle
Easterners, Central Asians, and Europeans”, while the ASI were unique to
India. The study also proved that most groups in India today can be
approximated as a mixture of these two populations, with the ANI
ancestry higher in traditionally upper caste and Indo-European speakers.
By itself, the study didn’t disprove the arrival of Indo-European
language speakers; if anything, it suggested the opposite, by pointing
to the genetic linkage of ANI to Central Asians.
However, this
theoretical structure was stretched beyond reason and was used to argue
that these two groups came to India tens of thousands of years ago, long
before the migration of Indo-European language speakers that is
supposed to have happened only about 4,000 to 3,500 years ago. In fact,
the study had included a strong caveat that suggested the opposite: “We
caution that ‘models’ in population genetics should be treated with
caution. While they provide an important framework for testing
historical hypothesis, they are oversimplifications. For example, the
true ancestral populations were probably not homogenous as we assume in
our model but instead were likely to have been formed by clusters of
related groups that mixed at different times.” In other words, ANI is
likely to have resulted from multiple migrations, possibly including the
migration of Indo-European language speakers.
The spin and the facts
But
how was this research covered in the media? “Aryan-Dravidian divide a
myth: Study,” screamed a newspaper headline on September 25, 2009. The
article quoted Lalji Singh, a co-author of the study and a former
director of the Centre for Cellular and Molecular Biology (CCMB),
Hyderabad, as saying: “This paper rewrites history… there is no
north-south divide”. The report also carried statements such as: “The
initial settlement took place 65,000 years ago in the Andamans and in
ancient south India around the same time, which led to population growth
in this part. At a later stage, 40,000 years ago, the ancient north
Indians emerged which in turn led to rise in numbers there. But at some
point in time, the ancient north and the ancient south mixed, giving
birth to a different set of population. And that is the population which
exists now and there is a genetic relationship between the population
within India.” The study, however, makes no such statements whatsoever —
in fact, even the figures 65,000 and 40,000 do not figure it in it!
This stark contrast between what the study says and what the media reports said did not go unnoticed. In his column for Discover
magazine, geneticist Razib Khan said this about the media coverage of
the study: “But in the quotes in the media the other authors (other than
Reich that is - ed) seem to be leading you to totally different
conclusions from this. Instead of leaning toward ANI being
proto-Indo-European, they deny that it is.”
Let’s leave that
there, and ask what Reich says now, when so much new data have become
available? In an interview with Edge in February last year, while
talking about the thesis that Indo-European languages originated in the
Steppes and then spread to both Europe and South Asia, he said: “The
genetics is tending to support the Steppe hypothesis because in the last
year, we have identified a very strong pattern that this ancient North
Eurasian ancestry that you see in Europe today, we now know when it
arrived in Europe. It arrived 4500 years ago from the East from the
Steppe…” About India, he said: “In India, you can see, for example,
that there is this profound population mixture event that happens
between 2000 to 4000 years ago. It corresponds to the time of the
composition of the Rigveda, the oldest Hindu religious text, one of the
oldest pieces of literature in the world, which describes a mixed
society…” In essence according to Reich, in broadly the same time
frame, we see Indo-European language speakers spreading out both to
Europe and to South Asia, causing major population upheavals.
The dating of the “profound population mixture event” that Reich refers to was arrived at in a paper that was published in the American Journal of Human Genetics in
2013, and was lead authored by Priya Moorjani of the Harvard Medical
School, and co-authored, among others, by Reich and Lalji Singh. This
paper too has been pushed into serving the case against migrations of
Indo-European language speakers into India, but the paper itself says no
such thing, once again!
Here’s what it says in one place: “The
dates we report have significant implications for Indian history in the
sense that they document a period of demographic and cultural change in
which mixture between highly differentiated populations became pervasive
before it eventually became uncommon. The period of around 1,900–4,200
years before present was a time of profound change in India,
characterized by the de-urbanization of the Indus civilization,
increasing population density in the central and downstream portions of
the Gangetic system, shifts in burial practices, and the likely first
appearance of Indo-European languages and Vedic religion in the
subcontinent.”
The study didn’t “prove” the migration of
Indo-European language speakers since its focus was different: finding
the dates for the population mixture. But it is clear that the authors
think its findings fit in well with the traditional reading of the dates
for this migration. In fact, the paper goes on to correlate the ending
of population mixing with the shifting attitudes towards mixing of the
races in ancient texts. It says: “The shift from widespread mixture to
strict endogamy that we document is mirrored in ancient Indian texts.”
So
irrespective of the use to which Priya Moorjani et al’s 2013 study is
put, what is clear is that the authors themselves admit their study is
fully compatible with, and perhaps even strongly suggests, Bronze Age
migration of Indo-European language speakers. In an email to this
writer, Moorjani said as much. In answer to a question about the
conclusions of the recent paper of Prof. Richards et al that there were
strong, male-driven genetic inflows from Central Asia about 4,000 years
ago, she said she found their results “to be broadly consistent with our
model”. She also said the authors of the new study had access to
ancient West Eurasian samples “that were not available when we published
in 2013”, and that these samples had provided them additional
information about the sources of ANI ancestry in South Asia.
One
by one, therefore, every single one of the genetic arguments that were
earlier put forward to make the case against Bronze Age migrations of
Indo-European language speakers have been disproved. To recap:
1.
The first argument was that there were no major gene flows from outside
to India in the last 12,500 years or so because mtDNA data showed no
signs of it. This argument was found faulty when it was shown that Y-DNA
did indeed show major gene flows from outside into India within the
last 4000 to 4,500 years or so, especially R1a which now forms 17.5% of
the Indian male lineage. The reason why mtDNA data behaved differently
was that Bronze Age migrations were severely sex-biased.
2. The
second argument put forward was that R1a lineages exhibited much greater
diversity in India than elsewhere and, therefore, it must have
originated in India and spread outward. This has been proved false
because a mammoth, global study of R1a haplogroup published last year
showed that R1a lineages in India mostly belong to just three subclades
of the R1a-Z93 and they are only about 4,000 to 4,500 years old.
3.
The third argument was that there were two ancient groups in India, ANI
and ASI, both of which settled here tens of thousands of years earlier,
much before the supposed migration of Indo-European languages speakers
to India. This argument was false to begin with because ANI — as the
original paper that put forward this theoretical construct itself had
warned — is a mixture of multiple migrations, including probably the
migration of Indo-European language speakers.
Connecting the dots
Two
additional things should be kept in mind while looking at all this
evidence. The first is how multiple studies in different disciplines
have arrived at one specific period as an important marker in the
history of India: around 2000 B.C. According to the Priya Moorjani et al
study, this is when population mixing began on a large scale, leaving
few population groups anywhere in the subcontinent untouched. The Onge
in the Andaman and Nicobar Islands are the only ones we know to have
been completely unaffected by what must have been a tumultuous period.
And according to the David Poznik et al study of 2016 on the
Y-chromosome, 2000 B.C. is around the time when the dominant R1a
subclade in India, Z93, began splintering in a “most striking” manner,
suggesting “rapid growth and expansion”. Lastly, from long-established
archaeological studies, we also know that 2000 BC was around the time
when the Indus Valley civilization began to decline. For anyone looking
at all of these data objectively, it is difficult to avoid the feeling
that the missing pieces of India’s historical puzzle are finally falling
into place.
The second is that many studies mentioned in this
piece are global in scale, both in terms of the questions they address
and in terms of the sampling and research methodology. For example, the
Poznik study that arrived at 4,000-4,500 years ago as the dating for the
splintering of the R1a Z93 lineage, looked at major Y-DNA expansions
not just in India, but in four other continental populations. In the
Americas, the study proved the expansion of haplogrop Q1a-M3 around
15,000 years ago, which fits in with the generally accepted time for the
initial colonisation of the continent. So the pieces that are falling
in place are not merely in India, but all across the globe. The more the
global migration picture gets filled in, the more difficult it will be
to overturn the consensus that is forming on how the world got
populated.
Nobody explains what is happening now better than
Reich: “What’s happened very rapidly, dramatically, and powerfully in
the last few years has been the explosion of genome-wide studies of
human history based on modern and ancient DNA, and that’s been enabled
by the technology of genomics and the technology of ancient DNA.
Basically, it’s a gold rush right now; it’s a new technology and that
technology is being applied to everything we can apply it to, and there
are many low-hanging fruits, many gold nuggets strewn on the ground that
are being picked up very rapidly.”
So far, we have only looked at
the migrations of Indo-European language speakers because that has been
the most debated and argued about historical event. But one must not
lose the bigger picture: R1a lineages form only about 17.5 % of Indian
male lineage, and an even smaller percentage of the female lineage. The
vast majority of Indians owe their ancestry mostly to people from other
migrations, starting with the original Out of Africa migrations of
around 55,000 to 65,000 years ago, or the farming-related migrations
from West Asia that probably occurred in multiple waves after 10,000
B.C., or the migrations of Austro-Asiatic speakers such as the Munda
from East Asia the dating of which is yet to determined, and the
migrations of Tibeto-Burman speakers such as the Garo again from east
Asia, the dating of which is also yet to be determined.
What is
abundantly clear is that we are a multi-source civilization, not a
single-source one, drawing its cultural impulses, its tradition and
practices from a variety of lineages and migration histories. The Out of
Africa immigrants, the pioneering, fearless explorers who discovered
this land originally and settled in it and whose lineages still form the
bedrock of our population; those who arrived later with a package of
farming techniques and built the Indus Valley civilization whose
cultural ideas and practices perhaps enrich much of our traditions
today; those who arrived from East Asia, probably bringing with them the
practice of rice cultivation and all that goes with it; those who came
later with a language called Sanskrit and its associated beliefs and
practices and reshaped our society in fundamental ways; and those who
came even later for trade or for conquest and chose to stay, all have
mingled and contributed to this civilization we call Indian. We are all
migrants.
Tony Joseph is a writer and former editor of BusinessWorld. Twitter: @tjoseph0010
