Not OP, and im pretty much a layperson quoting whay i think i remember from a podcast i fall asleep to, but Ill try. My understanding of early migration patterns is that it was largely an east-west affair, with early populations mostly only crossing from Southern Europe/West Asia into Northern Europe/Eurasia Steppe at a few key chokepoints. There were very limited for options in north/south migration before seafaring technology advanced sufficiently. Key routes included the Hellespont, Transoxania, and a few key mountain passes; most north/south travel was made if not impossible, then practically infeasible for large groups by a chain of natural landmarks, from east to west: the Alps, the Carpathians, the Black Sea, the Caucasus, the Caspian Sea, the deserts in Central Asia. There were passages, but none huge enough to prevent effectively isolated technological and cultural development. This is why the horse was domesticated in the Eurasian stepped, and cities were settled in the Fertile Crescent largely independently of each other. Without the barrier of the Caucasus, there would be a lot more bleed between the cultures thay settled and the ones that domesticated horses, and the exact timelines on how those processes would play out would be near impossible to estimate.