The Japanese-Jewish common ancestry theory (日ユ同祖論, Nichiyu Dōsoron) is a fringe theory that appeared in the 17th century as a hypothesis which claimed the Japanese people were the main part of the Ten Lost Tribes of Israel. A later version portrayed them as descendants of a tribe of Central Asian Jewish converts to Nestorian Christianity. Some versions of the theory applied to the whole population, but others only claimed that a specific group within the Japanese people had descended from Jews.