Aboriginal Australian is a collective term for all the indigenous peoples from the Australian mainland and Tasmania. This group contains many separate cultures that have developed in the various environments of Australia for more than 50,000 years. These peoples have a broadly shared, though complex, genetic history, but it is only in the last two hundred years that they have been defined and started to self identify as a single group. The exact definition of the term Aboriginal Australian has changed over time and place, with the importance of family lineage, self identification and community acceptance all being of varying importance. In the past Aboriginal Australians also lived over large sections of the continental shelf and were isolated on many of the smaller offshore islands, once the land was inundated at the start of the inter-glacial. However, they are distinct from the Torres Strait Islander people, despite extensive cultural exchange.