Tokyo | Japan's parliament enacted Friday a historic revision to the 19th century Imperial House Law by insisting only paternal-lineage men can become emperor, sparking fear that it could doom the already shrinking imperial family.

The revisions include adoption of distant male relatives to father future heirs and allowing princesses to keep their royal status after marrying commoners.

Emperor Naruhito's 24-year-old daughter is hugely popular, and many Japanese want her to be his successor. Princess Aiko is ineligible because she is a woman.

Japan's male-only succession rule means the emperor's teenage nephew and second in line, Prince Hisahito, will probably be the heir. (AP)