New Delhi, July 17 -- 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.

Royal watchers and experts fear the new measures could doom the 1,500-year-old hereditary institution by insisting that only men can be emperor, sparking worry about the shrinking, fast-aging imperial family.

Emperor Naruhito 's 24-year-old daughter is hugely popular, and many Japanese want her to be his successor, but Princess Aiko is inel...