Neanderthals, Denisovans and our species (Homo sapiens) are commonly cited as closely related subspecies, even interbreeding with each other. Yet our species theoretically didn't migrate out of Africa until about 60,000 years ago, whereas Neanderthals were living in Europe a few hundred thousand years ago. Did they evolve out of Homo habilis, which migrated out of Africa before our species?
This suggests that Neanderthals must have evolved from Homo sapiens (or perhaps Homo habilis) stock in Africa before migrating out of Africa to Europe. However, conventional wisdom suggests that Neanderthal morphology was shaped by Ice Age Europe.
One possibility is that they evolved into a distinct subspecies in Africa, then migrated into Europe, where continuing evolution turned them into the familiar Neanderthals. But wouldn't this mean that Homo sapiens (the ancestor of Neanderthals) then migrated out of Africa hundreds of thousands of years ago?
Is this simply a question that hasn't been resolved, or is there a popular theory that explains the origin of Neanderthals and Denisovans?