Little Steppe earthquakes: upheavals both demographic and scholarly

Silent all these years, ancient Yamnaya DNA finally speaks in groundbreaking preprint on the origins of Indo-Europeans

You can toil a whole long career at the bleeding edge of a field while it only ever advances at an imperceptible pace. And then as unpredictably as a massive earthquake, overnight some external factor can shake up, overturn or catapult forward every painstaking insight earned up to that point. In 1786, William Jones, a British judge in India, first presented a theory to a meeting of the Asiatic Society of the East India Company, previously at most unsystematically mooted by European missionaries and traders to India. Jones argued that Europe and India’s various languages shared a common root. In the 19th century, philologists like Max Müller would subject this idea of underlying commonality from the Atlantic shore to the Indian one, to further examination. But after 1900, the idea of Indo-Europeans was co-opted from the obscure margins of academia and thrust to center stage of all Western culture. Aryans, to use the classical Indian endonym, were suddenly held up as an ancient culture-bearing super-race, an ethnos whose legend was soon supercharged to truly sinister ends by racist ideologies. In the wake of the Nazi regime’s horrors, what had been an entirely value-neutral academic exploration into deep Eurasian linguistic and genetic roots was left tainted and in utter disrepute.

Thus tarnished by association, after World War II, the origin story of the languages over 40% of us speak today languished long-term in the margins and shadows. Ineluctably connected to the unfashionable phenomenon of mass migration, the study of Indo-Europeans as a people was left to a few unswerving scholars like Lithuanian-American archaeologist Marija Gimbutas who soldiered on resolutely in their academic ghetto, undeterred by their core theory’s popular tarring and unshakable air of disrepute. And lest my portrayal be dismissed as hyperbolic, consider that at one point, theorizing about Indo-European steppe roots was so disreputable, Gimbutas, a UCLA professor, could find no mainstream publisher for much of her anthropological work; the only person willing to publish The Journal of Indo-European Studies was a literal white supremacist. 

In this climate of denialism and marginalization, it was left to Gimbutas and her intellectual heirs, J. P. Mallory and David Anthony, to first train modern archaeological methods on the questions of the emergence and later expansion of proto-Indo-Europeans, the race that would go on to shape the ethnolinguistic parameters of much of the modern world. Gimbutas famously argued, correctly as it turns out, that Indo-European languages arrived with nomadic pastoralists from the Pontic steppe of modern Ukraine. This was a culture that inhumed their elite dead in vast burial mounds, kurgans, manmade hillocks that stippled the landscape of the western steppe, a trademark on a massive scale that would prove invaluable for later scholars. A nomadic, pre-literate culture's answer to the rooted Pharaohs' treasure-laden crypts, kurgans bore eloquent testimony to the progress of a people who denominated their achievements in kilometers conquered rather than wealth accumulated. And crucially they would eventually yield the ancient DNA that has a way of settling debates once and for all.

But ancient DNA’s day was yet to come at the turn of this century. The state of the field at that point was all theory, built around educated guesswork and an unstructured mass of both facts from archaeology and insights from historical linguistics. Mallory’s In Search of the Indo-Europeans (1991) and Anthony’s The Horse, Wheel and Language (2007) walked a fine line, mustering all the tools of 20th-century scholarship in support of Gimbutas’ model, but stymied by the field’s anti-migrationist mainstream that dismissed their attempts to correlate pots with people. Gimbutas died in 1994, before the DNA revolution came to archaeology. And then to nearly everyone’s surprise the pendulum swung back sharply in 2015 with the publication of two papers utilizing ancient DNA that showed definitively and without a shadow of a doubt that the people buried in the kurgans contributed 50% of ancestry to modern Northern Europeans, 35% to Southern Europeans, and 10-20% to Asian populations from Iran to India. This was no trickle of migration, it was Gimbutas’ migration on a mass scale, overnight overturning the demographic, genetic and cultural order of northwest Eurasia 5,000 years ago. Forget pots, a new people had flooded the land: the fearsome nomadic Yamnaya of the Pontic steppe.

Over the last decade, researchers have been probing the details of the regional migrations that were knock-on consequences of that initial explosion out of the Pontic steppe, from the Beaker people's arrival to Britain, to the expansion of Aryans in Central and South Asia. But the precise origins of the Yamnaya, the first fully nomadic culture on the Eurasian steppe, the propulsive force behind he Indo-European expansions that began 5,000 years ago, remained nebulous. We know that in 3500 BC the Yamnaya were just one among many pastoralist people of the Pontic steppe, but within five centuries their descendents could be found ascendant and thriving everywhere from the grasslands of Hungary to the pastures of the Mongolian Altai. Their cultural and genetic heirs in Europe and Asia would beget the numerous Indo-European tribes, but after 2500 BC, in their actual steppe homeland, the Yamnaya themselves seem to have faded as a force. The Yamnaya conquered on a scale not seen before, but in time, they too were supplanted.

Within less than a decade of publishing one of those above-mentioned papers preliminarily establishing the fact of Indo-European expansion, David Reich’s lab has now posted a preprint probing the depths of Yamnaya genetic history with astonishing granularity. The Genetic Origin of the Indo-Europeans answers the questions of when, where and from whom the Yamnaya came. This preprint also shines a bright light on the origins of the Hittite people of Bronze Age Anatolia, and how they were related to other Indo-Europeans. With this research, our ignorance of the two millennia before the Yamnaya explosion of 3000 BC, whether willful or because data and methods lagged theory, is truly a thing of the past. This is the massive earthquake a scholar can only hope for; overnight it catapults forward those theories Gimbutas, Mallory and Anthony had been patiently refining over decades. 

From the gates of the Caspian to Europe’s edge

With the reconceptualization of human history since 2010 through population genetics and ancient DNA has always come an alphabet soup of opaque acronyms to reference ancient peoples long extinct, but who played key roles in the ethnogenesis of those successor populations. For example, ANE has long referred to “Ancient North Eurasians,” a group of Paleo-Siberians whose genetic imprint is seen from Portugal to Patagonia, but no longer exists anywhere in undiluted form; ANE DNA is everywhere today, but only as an essential ingredient in the pooled ancestry composition of other groups. These “lost races” are often conceptualized as distinct breeding populations, and in some cases that is perfectly fair. For example, the Beringians who begat modern Native Americans were an isolated group of mammoth hunters who were for millennia genetically separated from their Siberian cousins. But elsewhere the acronyms archaeogeneticists use are simply convenient if opaque labels for observable statistical patterns. And those patterns may not ever actually correlate with an identifiable real-world population (for example, “Basal Eurasians”). 

To sidestep those conventions that have tended to misleadingly emphasize unrealistically discrete clusters, in “The Genetic Origin of the Indo-Europeans” Reich’s group chose to model the Yamnaya’s antecedents as situated among a series of clines, genetic gradients that reflect gene flow between populations. These are easily delineated in the principal components analysis above, with individual genotypes positioned on a two-dimensional plot where geometric distance correlates transparently with genetic distance. Clines are what emerges when you have numerous populations continuously interbreeding with their near neighbors; the further apart two populations lie on a clinal landscape, the more genetically distinct they are, but without ever a sharp break at any intermediate juncture. Over seven millennia ago, the broad zone of Ukraine and Russia north and east of the Black Sea across which the Yamnaya would later range was defined by three major genetic clines.

First was the Volga cline, comprising a set of populations starting in the Volga river basin and continuing north toward the Urals; this cline is defined by a progressively increasing proportion of Eastern hunter-gatherer (EHG) ancestry. The EHG seem to have been the dominant foragers in the broad swath of territory between the Baltic and Black Seas as the Holocene dawned 11,700 years ago, and they themselves were on a cline defined at the other end by Western hunter-gatherers (WHG), who dominated Europe from the Balkans to Britain. Though most EHG ancestry seems to have in turn been Ancient North Eurasian (ANE), their presence on Europe’s fringe also resulted in minority gene flow from the WHG, which shifted the EHG genetic profile toward more western and southern populations than their Paleo-Siberian cousins. The other population on this cline were the occupants of the lower Volga. This population had not been genotyped before the work that went into this preprint, and their ancestry seems best understood as a combination of other groups and clines: foremost amongst these, ancient Caucasus hunter-gatherers (CHG), but also Siberians, Central Asians and EHG foragers from the north. The populations of the lower Volga anchor the northern edge of the second cline, which reaches south to the Caucasus mountains. This is the Caucasus-Lower Volga (CLV) cline, and variation along it is to a great extent driven by Neolithic-era gene flow from West Asia that superseded, assimilated or was absorbed by earlier CHG-dominated populations. 

The third cline is defined by admixture between lower Volga populations and the indigenous foragers of the Dnieper river basin, the Dnipro cline. These foragers, the Ukrainian Neolithic hunter-gatherers (UNHG) occupy a genetic position between the EHG and WHG. This cline is relevant mostly because it appears to be the most likely region for the ethnogenesis of the early Yamnaya, and their distinctiveness is in part their admixture with UNHG.