Blood group B has its highest frequency in South Asia where it ranks first as the largest share of the earth's population. In Southeast Asia the share of the population is high, especially in Thailand and Indonesia, then in East Asia, Northern Asia and neighboring Central Asia, and its incidence diminishes both towards the west and the east, falling to single digit percentages in Netherlands, Norway and Portugal.[38][39] It is believed to have been entirely absent from Native American and Australian Aboriginal populations prior to the arrival of Europeans in those areas.[39][40]