The evolution of our species, Homo sapiens, took place within the past 200,000 years or so and recent research indicates that in East Africa, where Homo sapiens are thought to have originated, the trend towards greater aridity began around 660,000 years ago. It is thought that this general trend towards increased aridity had an important influence on the dispersal of early humans from their presumed original homeland. In addition to its alternate periods of heat and cold, natural movements of the Earth's crust have changed the shape of landmasses, flooding areas that were once dry land and creating continents and even mountains from areas that were once deep below the ocean. Migration to Australia took place during the closing stages of the