The Anatolian hypothesis of Proto-Indo-European origin is that the speakers of the Proto-Indo-European language lived in Anatolia during the Neolithic era. When the Neolithic Revolution took place in the seventh and sixth millennia BC, the speakers spread over Europe. Those who advocate this hypothesis think that the Indo-European languages originated in Anatolia. They believe that the Proto-Indo-Europeans then migrated north to the location north of the Caucasus Mountains. There is an another hypothesis, called the Kurgan hypothesis. The people who support it say the Indo-European languages came from the Caucasus. One of the best-known advocates of the Anatolian hypothesis is Colin Renfrew.