> it seems that the PIE culture itself was the result of early agriculturalists in the Pontic steppes being invaded by ousiders from farther up north in Eurasia

> it seems that the PIE culture itself was the result of early agriculturalists in the Pontic steppes being invaded by ousiders from farther up north in Eurasia - known only from molecular-level evidence, and labeled the "ancient north Eurasians" Can you cite this, please?