The oldest surviving cultural traditions of Australia—and some of the oldest surviving cultural traditions on earth—are those of Australia's Aboriginal and Torres Strait Islander peoples. Their ancestors have inhabited Australia for between 40,000 and 60,000 years, living a hunter-gatherer lifestyle. In 2006, the Indigenous population was estimated at 517,000 people, or 2.5 per cent of the total population. Most Aboriginal Australians have a belief system based on the Dreaming, or Dream time, which refers both to a time when ancestral spirits created land and culture, and to the knowledge and practices that define individual and community responsibilities and identity. Conflict and reconciliation between indigenous and non-indigenous Australians has been a source of much art and literature in Australia, and ancient Aboriginal artistic styles and iconic inventions such as the boomerang, the didgeridoo and Indigenous Australian music have become symbols of modern Australia.