Why every single Japanese person might be surnamed Sato in 500 years

In just five centuries, every Japanese person will share the same family name: Sato.

That is the prediction of professor Hiroshi Yoshida, based on a simulation that takes into account current trends, cultural norms and the legal requirement that husbands and wives must have the same family name.

“I began by gathering data on the share of different surnames in 2022 and 2023 and was able to determine that 1.529 per cent of the Japanese population had the name ‘Sato’ in 2023,” Yoshida said.

That was 0.83 per cent higher than in 2022, he said, as a result of marriage, divorce, birth and death.

About 504,000 couples got married in 2022, according to the ministry of welfare, of which 94.7 per cent took the husband’s family name.

As a result, the maiden names of some 478,00 women were erased and, in the case of families in which the daughter is an only child, some ancient family names effectively disappeared.

Yoshida has calculated that if the annual rate of increase continues unabated, half of all Japanese will be Satos by the year 2446 and 100 per cent of the population in 2531.

Under Article 750 of the Japanese Civil Code, a husband and wife are required to have the same surname after marriage. Japan is the only country that requires both members of a married couple to share the same surname by law.

Yoshida says that virtually all couples take the husband’s name due to long-standing social norms.

“This is very much part of the cultural heritage of the samurai era in Japan,” he said. “In the old days, only a man could be a samurai and only his son could continue the family name, so women effectively did not have their own names.”

And while the law today does not forbid a couple from keeping the women’s family name, Yoshida said