Indo-European languages—including English, Spanish, German, Greek, Hindi, Bengali, Russian, Persian, Gaelic and more than 400 others—are the largest language family on Earth, with almost 3 billion native speakers.

Scholars have spent centuries trying to trace the roots of these varied but related tongues. One longstanding question has been how, when and by whom a reconstructed precursor language called proto-Indo-European was brought into Europe.

Lately, the debate has come down to a tug-of-war between the “Anatolian hypothesis,” which posits that farmers from what is now Turkey brought proto-Indo-European with them along with agriculture when they migrated into Europe between 8,000 and 9,500 years ago, and the “steppe hypothesis,” which points instead to herders on the Eurasian steppe between 5,000 and 6,000 years ago.