Japanese people to all have same surname by 2531 unless marriage laws change, study shows

Japanese people will all have the same surname by the year 2531 because of the country's laws around marriage, a new study has revealed.

Professor Hiroshi Yoshida of Tohoku University's Center for Research on Aging, Economy and Society projected that current Japanese marriage laws will mean every citizen will be known as 'Sato-san' in just over 500 years.

“If everyone becomes Sato, we may have to be addressed by our first names or by numbers, I don’t think that would be a great world to live in," Professor Yoshida said, according to the Japanese newspaper Mainichi.

'Sato' is the most common surname in Japan, reportedly making up 1.5% of the population.

According to Prof Yoshida's study, the number of people with the surname Sato in the population increased by 1.0083% between 2022 and 2023.

If the rate remains the same, around half of Japan's population will take the surname by 2446 and all will have it by 2531.

Prof Yoshida's calculations were made by analysing the population growth rate and demographic trends of the surname "Sato", but conceded he made several assumptions which caused limitations to the research.

The study was driven to promote awareness for Professor Yoshida's initiative - called the ThinkNameProject - which hopes to address Japan's historic marriage laws.

Japan is the only country with a law requiring couples to adopt the same surname once married.

The 19th century law doesn’t specify which spouse should change their surname, but an overwhelming majority of women take their husband’s.

Many women, gender equality experts, and even a United Nations committee have called these laws outdated and called for change.

Over the years, several couples who wanted to keep their own names have gone to the Japanese Supreme Court to challenge the law but all have been dismissed.

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