This is more or less what Yuval Noah Harari lays out in the first section of his book 'Sapiens': 1 - homo sapiens have a cognitive revolution 70k years ago which makes them able to think and communicate in more sophisticated ways. 2 - homo sapiens spread all around the world and wipe out ~all the large animals (including other human species..). His evidence from various places (Australia, America, various islands) of humans arriving then the large animals disappearing is pretty convincing.