A real language lies behind reconstructed Proto-Indo-European, just as a real language lies behind any dictionary. And that language is a guide to the thoughts, concerns, and material culture of real people who lived in a definite region between about 4500 and 2500 BCE.

Perhaps the first major horse-based society in Eurasia was the Yamnaya people, hypothesized to have emerged as an admixture of hunter-gatherers from the Caucasus and Eastern Europe. Their territory was the northern Caucasus between the Black Sea and the Caspian Sea (known as the Pontic-Caspian Steppe).

Forager languages were more apt to decline in the face of agricultural immigration. Farmers had a higher birth rate; their settlements were larger, and were occupied permanently. They produced food surpluses that were easier to store over the winter.