Around the world today, there are about 440 living languages that descend from an original Indo-European mother tongue. Where that mother tongue, Proto-Indo-European, originated is debated.
The Kurgan hypothesis says that Indo-Europeans were associated with the Yamna culture on the Pontic-Caspian Steppe, north of the Black and Caspian Seas. From there, the Kurgan hypothesis says, they spread with the domestication of horses beginning around 6,000 years ago. The steppe nomads used the new-fangled horse technology to conquer non-horse people, basically.
The Anatolian hypothesis – also called the Renfrew hypotheis – thinks that Proto-Indo-European originated in Anatolia. What is today Turkey. The Anatolian hypothesis says the language began spreading out much earlier than the Kurgan hypothesis, roughly 9,500 to 8,000 years ago, and that the migrations were peaceful instead of horse-enabled conquests.
Recent genetic analyses think the hypotheses may not contradict each other after all. People of the Kurgan steppe region, genetically, descended at least in part from migrants from the Middle Eastern Neolithic who immigrated to the steppe from Anatolia. Was there an early migration to the steppe? Did that first migration’s descendants eventually fan out across Europe, the Middle East, and India? More research is needed.
One thing archaeology can definitely tell us: Proto-Indo-European is tied with Neolithic migrations and the agricultural revolution. It definitely did not expand before then.
