The relatively shallow waters of the continental Sunda Shelf of Southeast Asia end at a line drawn through the Straits of Lombok, northwards through the Straits of Makassar, between the island of Palawan and the remainder of the Philippines, then south of Taiwan. To the east of this line are deep water channels that have always isolated the islands of Sulawesi, the Philippines, Timor and other islands of the Moluccas. Further east we come to the shallow Sahul Shelf between New Guinea and the north coast of Australia, once a land bridge for marsupials and also for humans. Whereas land mammals and freshwater fishes were restricted by these narrow seas, humans spread from the Sunda to the Sahul Shelf at least 50,000 years ago when sea-levels were lower than now and sea-crossings were perhaps shorter as a result of the build-up of glacial ice sheets. Even so, people must have crossed at least 70 km of open sea in order to reach Sahul. We may infer that they used bamboo rafts because these are an easily constructed form of transport and they could be made with the crude stone tools then available. There is no problem about movement over these relatively enclosed seas because the winds and currents reverse every season with the monsoons.