Theories about the royal lines of the Yamato Kingdom include that it originated from Himiko and Toyo; that the first royal line ended with Iyo and a new one appeared; that the royal line during the beginning of the Yamato Kingdom was not heredity but was shared between different powerful families; that the first royal line died out and Mimakiirihiko (Emperor Sujin) started a new one around the beginning of the fourth century.
卑弥呼-台与の王統を継承しているとする説、壱与で王統が断絶し新たな王統が発生したとする説、初期ヤマト王権の王位は世襲ではなく有力豪族間で継承されたとする説、初期の王統は途中で断絶して4世紀前期ごろにミマキイリヒコ（崇神天皇）が新たな王統を開始したとする説などがある。