We have identified evidence that the disappearance of Neanderthals in the Caucasus coincides with a volcanic eruption at about 40,000 BP. …  The coeval volcanic eruptions (from a large Campanian Ignimbrite eruption to a smaller eruption in the Central Caucasus) … forced the fast and extreme climate deterioration (“volcanic winter”) of the Northern Hemisphere. … The most significant advantage of early modern humans over contemporary Neanderthals was geographic localization in the more southern parts of western Eurasia and Africa. … Major technological and social innovations [appeared] shortly after 40,000 BP. (more)

More evidence that disasters matter, and evolution can be pretty random.