The mystery of the Sintashta people

During the Middle to Late Bronze Age, the steppes southeast of the Ural Mountains, in what is now Russia, were home to communities of metallurgists who buried their warriors with horses and the earliest examples of the spoked-wheel battle chariot.

We don't know what they called themselves, because they didn't leave any written texts, but their archaeological culture is commonly known as Sintashta. It was named after a river near one of their main settlements; an elaborate fortified town that has also been described as an ancient metallurgical industrial center. Another of their well known settlements, very similar to Sintashta, is Arkaim, pictured below courtesy of Wikipedia.

Sintashta is arguably one of the coolest ancient cultures ever discovered by archaeologists. It's also generally accepted to be the Proto-Indo-Iranian culture, and thus linguistically ancestral to a myriad of present-day peoples of Asia, including Indo-Aryans and Persians. No wonder then, that its origin, and that of its population, have been hotly debated issues.

The leading hypothesis based on archaeological data is that Sintashta is largely derived from the more westerly and warlike Abashevo culture, which occupied much of the forest steppe north of the Black and Caspian Seas. In turn, Abashevo is usually described as an eastern offshoot of the Late Neolithic Corded Ware Culture (CWC), which is generally seen as the first Indo-European archaeological culture in Northern Europe (see here).

Below is a Principal Component Analysis (PCA) featuring 38 Sintashta individuals from the recent Narasimhan et al. 2018 preprint. Note that the main Sintashta cluster overlaps almost perfectly with the main CWC cluster. The relevant datasheet is available here.

Moreover, many ancient and present-day South and Central Asians, particularly those identified with or speaking Indo-Iranian languages, appear to be strongly attracted to the main Sintashta cluster, forming an almost perfect cline between this cluster and the likely Indus Valley diaspora individuals who show no evidence of steppe ancestry.

This is in line with mixture models based on formal statistics showing significant Sintashta-related ancestry in Indo-Iranian-speakers (for instance, see here), and high frequencies of Y-haplogroup R1a-Z93 in both the Sintashta and many Indo-Iranian-speaking populations.

Some of the Sintashta samples are outliers from the main Sintashta cluster, and that's because they harbor elevated levels of ancestry related to the Mesolithic and Neolithic foragers of Eastern Europe and/or Western Siberia. This is especially true of a pair of individuals who belong to Y-haplogroup Q. However, this doesn't contradict archaeological data, which suggest that the Sintashta community may have been multi-cultural and multi-lingual. Indeed, it's generally accepted based on historical linguistics data that there were fairly intense contacts in North Eurasia between the speakers of Proto-Indo-Iranian, Proto-Uralic and Yeniseian languages.

Thus, it appears that there's not much left to debate because ancient DNA has seemingly backed up the most widely accepted hypotheses about the origin of Sintashta and its people, and their identification mainly as Proto-Indo-Iranian-speakers.

However, a sample from a Sredny Stog II culture burial on the North Pontic steppe, in what is now eastern Ukraine, has complicated matters somewhat. This individual, known as Ukraine_Eneolithic I6561, not only clusters very strongly with the most typical Sintashta samples, but also belongs to Y-haplogroup R1a-Z93. On the other hand, none of the CWC remains sequenced to date belong to this particular subclade of R1a (although, obviously, they do belong to a host of near and far related R1a subclades).

I've never seen anyone worth reading propose that Sintashta might derive from Sredny Stog II instead of Abashevo. And no wonder, because Sredny Stog II was long gone when Sintashta appeared in the archaeological record.

But if CWC remains continue to fail to produce R1a-Z93, while, at the same time, the steppes of eastern Ukraine and surrounds are shown to be a hotbed of R1a-Z93 from the Sredny Stog to the Sintashta periods, which I think is possible, then ancient DNA might well force a serious re-examination of how the awesome Sintashta culture and people came to be.

See also...