Thousands of years ago human beings trekked the 2,000 kilometres across the "ice-free corridor" from Siberia through to the Americas. This last great continental colonisation has now become the subject of a computerised model at the University of Southampton.
Mathematicians, archaeologists, computer scientists and ecologists have collaborated to look at human beings as a colonising species.
Archaeologists have studied the clues left behind by these early hunter-gatherers, compiling radiocarbon dates from early sites.
Ecologist Jonathan Adams has compiled vegatation maps of the Americas at 1,000-year intervals from 18,000 to 10,000 years ago - vegetation reconstructions that have subsequently been put on the world wide web. Mathematicians and scientists have put all this together to create a computer simulation programme which models human range expansion.
Clive Gamble, professor of archaeology at Southampton and one of the project leaders, says: "These people had been used to hunting mammoths in Siberia and then hit this superabundant environment in the Americas. We have evidence that large numbers of species died out as human beings arrived, and, while we don't actually have the smoking gun, the circumstantial evidence for the complicity of human beings in this slaughter is very strong."
But James Steele, an archaeologist involved in the computing, added: "There is evidence that the arrival of human beings coincided with a temporary aridification of the land - so the animals may well have been weakened."
"What is so fascinating is that they moved so quickly," said Professor Gamble. Radiocarbon dating indicates that people moved five to 15 kilometres a year. "They managed the switch to a more sustainable relationship with the now impoverished fauna - so the ultimate message is an optimistic one."
Migrations such as this meant that by the time the European explorers began to discover the rest of the world, they found a full planet.