Human habitation of the Australian continent is estimated to have begun around 65,000 to 70,000 years ago, possibly with the migration of people by land bridges and short sea-crossings from what is now Southeast Asia. These first inhabitants may have been ancestors of modern Indigenous Australians. At the time of European settlement in the late 18th century, most Indigenous Australians were hunter-gatherers with complex economies and societies. Indigenous Australians have an oral culture with spiritual values based on reverence for the land and a belief in the Dreamtime. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists and hunter-gatherers. The northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia.