Aboriginal migration from South East Asia is the beginning of Austrahan economic history. Prehistorians have tended to focus on means to sea travel rather than opportunity and motive to migrate. American and Australian measures of sea depth contours throw new light on possible migration paths and the conditions that might have prompted Aboriginal ancestors to move through island SE Asia to Australia. Interpretation of the data depends on a reconsideration of palaeodemography and the introduction of some economic and historical analysis. Several scenarios suggest possible conditions influencing trends and fluctuations in Aboriginal migration over the past 60,000 years.