It is important here to acknowledge that at the time of contact it is estimated that the Aboriginal population was approximately 250,000 to 300,000 separated into around 250 language groups each with its own sub-groups and specific dialects (around 600 different language groups overall). Because of the dynamic nature of Aboriginal cultures, there were and continue to be, differences between the groups. There are, however, shared cultural traits, economic and ceremonial dealings, and a customary system of land-tenure law. Land was and is central to spiritual/religious life, as is clearly demonstrated within the concept of The Dreaming. Land is also the primary basis of economic survival.