Matt pointed me to the fact that the paper that’s going to come out:
Horse domestication fundamentally transformed long-range mobility and warfare. However, modern domesticates do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling at Botai, Central Asia ~3,500 BCE (Before Common Era). Other long-standing candidate regions for horse domestication, such as Iberia and Anatolia, were also recently challenged. Therefore, the genetic, geographic and temporal origins of modern domestic horses remained unknown. Here, we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they rapidly expanded across Eurasia from ~2,000 BCE, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioral adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe ~3,000 BCE driving the spread of Indo-European languages. This contrasts with the situation in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium BCE Sintashta culture.
If you have an interest in the domestic horse (I have) you are aware it’s the product of massive demographic radiation from a small founder population. With ancient DNA we now know where it started: with the Sintashta people of the Volga to the Ural steppe 4,000 years ago.
This is not totally surprising, because we know that the Sintashta were highly warlike and they invented the light war-chariot. This technology spread across the whole Old World, from Egypt to China to Ireland. In some cases, I believe that this was mediated directly by the Sintashta, the early Indo-Iranians. Not only were the Mitanni elite of Syria 3,500 years ago speaking an Indo-Aryan/Iranian language, and worshipping Indo-Aryan/Iranian gods but genetically some of them retained their steppe character. The Sintashta also had domestic dogs, but the lineage of these dogs persists only in China today. Not coincidentally, light war-chariots that are clearly copied from the Iranian-style vehicles show up in Shang China in 1200 BC.
The genetic/demographic impact won’t be visible in many areas. Perhaps Indo-Iranian mercenaries arrived in a city-state, and eventually taught the natives how to build, maintain, and utilize war chariots? This seems plausible. To this day we aren’t quite sure where the wagon was invented because it spread almost immediately over much of Western Eurasia 5,500 years ago.
We also have to remember that the “Iranian” zone of domination was far wider in antiquity than in the present. Around 500 BC Scythians were present as far east as Mongolia, as far west as Hungary, and as far south as northern Iran itself. This means that they could easily have spread the chariot within their own cultural-zone and then it was rapidly adopted by adjacent groups to the east, west, and south.
Related: check out my steppe series.