He developed the Anatolian hypothesis, which argues that Proto-Indo-European, the reconstructed ancestor of the Indo-European languages, originated approximately 9,000 years ago in Anatolia and moved with the spread of farming throughout the Mediterranean and into central and northern Europe. This hypothesis contradicted Marija Gimbutas's Kurgan hypothesis, which states that Proto-Indo-European was spread by a migration of peoples from the Pontic–Caspian steppe approximately 6,000 years ago. Recent work on ancient DNA has indicated a link between the populations featured in Gimbutas's hypothesis – without, however, providing a direction of spread.