The puzzle is one of the greatest surrounding our species. On a planet that bristled with different types of human being, including Neanderthalsand the Hobbit-like folk of Flores, only one is left today: Homo sapiens.
Our current solo status on Earth is therefore an evolutionary oddity – though it is not clear when our species became Earth's only masters, nor is it clear why we survived when all other versions of humanity died out. Did we kill off our competitors, or were the others just poorly adapted and unable to react to the extreme climatic fluctuations that then beset the planet?
These key issues are to be tackled this week at a major conference at the British Museum, in London, called When Europe was covered by ice and ash. At the meeting scientists will reveal results from a five-year research programme using modern dating techniques to answer these puzzles.
In particular, researchers have focused on the Neanderthals, a species very close in physique and brain size to modern humans. They once dominated Europe, but disappeared after modern humans emerged from our African homeland around 60,000 years ago. The question is: why?
"A major problem in understanding what happened when modern humans appeared in Europe has concerned the dates for our arrival," said Professor Chris Stringer, of the Natural History Museum, London. "It was once thought we appeared in Europe around 35,000 years ago and that we coexisted with Neanderthals for thousands of years after that. They may have hung on in pockets – including caves in Gibraltar – until 28,000 years ago, it was believed."