Aboriginal Australians are the various indigenous peoples of the Australian mainland, Tasmania, and often the Tiwi Islands. This group contains many distinct peoples that have developed across Australia for over 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 definition of the term "Aboriginal" 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 lived over large sections of the continental shelf and were isolated on many of the smaller offshore islands when the land was inundated at the start of the inter-glacial. However, they are considered distinct from the Torres Strait Islander people, despite extensive cultural exchange.