What happened when we expanded out of Africa and into Asia -- where did we go and whom did they meet along the way? The latest evidence suggests we left far earlier than previously thought and interbred with a newly-discovered type of ancient human -- the Denisovans. The existence of these people was only established four years ago, when geneticists extracted DNA from a tiny fragment of finger bone. And because our ancestors mated with them, their genes found a home within our DNA. More than that, they've helped us survive and thrive. survive and thrive. Australia - When Homo sapiens arrived in Australia, they were - for the first time - truly alone, surrounded by wildly different flora and fauna. How did they survive and populate a continent? There is a close cultural and genetic link between the First Australians and modern-day Aborigines -- the ancient and modern story intersect here as nowhere else in the world. The secret to this continuity is diversity. Intuitively, they found the right balance between being separate and connected.