I don't buy that, but no other explanation has yet to arise. But the possibility that there is another explanation (Atlantis-like civilization) is available to us and demands some investigation. The world currently has vastly advanced civilizations living a scant few hundred miles from mud brick villages and grass roofed shacks, why not then?
Another curiosity is that we are led to believe that moder humans appeard little more than 30k years ago and we have advanced to our current stage since. By Darwinian theories of evolution this is not possible. By biblical histories, this is not possible. Yet again though, another option has not yet surfaced. We should keep an open mind to possibilites that do explain these events with more logic though.
Atlantis may not be a "missing step" in this logical process but a previously unrecorded civilization would be a logical step.
But, that's just my opinion... I could be wrong.