A new study suggests that in 500 years, all Japanese people could have the same last name 'Sato'. This might happen if the law doesn't change. Right now, the law says that married couples must share the same last name. This law is from the late 1800s. The study was conducted by the Think Name Project and Hiroshi Yoshida, a professor at Tohoku University. They want to show people what could happen if the law doesn't change.

Yoshida said, "If everyone becomes Sato, we may have to be called by our first names or by numbers. I don't think that would be a good world to live in." Right now, 'Sato' is the most common last name in Japan. It is the last name of 1.5% of the people.

When people get married in Japan, they have to choose a last name to share. In 95% of marriages, the woman changes her name. But, the government lets women use their old names on important documents like passports and driving licenses. Some people in the government think changing the law would cause problems in families and confuse children.