Human habitation of the Australian continent is estimated to have begun between 42,000 and 48,000 years ago, possibly with the migration of people by land bridges and short sea-crossings from what is now South-East 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 a complex oral culture and spiritual values based on reverence for the land and a belief in the Dreamtime. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturalists and hunter-gatherers. The northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia.