The human presence on the island dates back at least 40,000 years to the oldest human migrations out of Africa. Research indicates that the highlands were an early and independent center of agriculture, with evidence of irrigation going back at least 10,000 years.Because of the time depth of its inhabitation and its highly fractured landscape, an unusually high number of languages are spoken on the island, with some 1,000 languages (a figure higher than that of most continents) having been catalogued out of an estimated worldwide pre-Columbian total of more than 7,000 currently spoken human languages according to Ethnologue. Most are classified as Papuan languages, a generally accepted geographical term. A number of Austronesian languages are spoken on the coast and on offshore islands.