Everyone in Japan will be called Sato by 2531 unless marriage law changed, demographics professor warns

A new study suggests that all Japanese citizens will share the same family name in 500 years unless married couples are allowed to use separate surnames, reports The Guardian.

The study, led by Hiroshi Yoshida, a professor of economy at Tohoku University, indicates that if Japan continues to require couples to choose a single surname, every Japanese person will be called "Sato-san" by 2531.

Yoshida acknowledged that his projections were based on certain assumptions but emphasised the importance of using data to illustrate the potential impact of the current system on Japanese society.

"If everyone becomes Sato, we may have to be addressed by our first names or by numbers," he said, according to the Mainichi. "I don't think that would be a good world to live in."

Sato is already the most common Japanese surname, representing 1.5% of the total population, according to a March 2023 survey, followed closely by Suzuki.

Some social media users mistakenly believed the study, first reported on Monday but published in March, was an April Fools' Day prank. However, Yoshida clarified that his goal was to provoke contemplation on the issue.

He stated that a nation of Satos "will not only be inconvenient but also undermine individual dignity," according to the Asahi Shimbun. He added that this trend would also result in the loss of family and regional heritage.

According to Yoshida's calculations, the proportion of Japanese people named Sato increased by 1.0083 times from 2022 to 2023. Assuming this rate remains constant and there are no changes to the surname law, approximately half of the Japanese population will have the surname Sato by 2446, increasing to 100% by 2531.

In Japan, couples must decide which surname to use when they marry, but in 95% of cases, the woman changes her name.

However, the situation would be different if the Japanese government yielded to increasing pressure to allow married couples to use separate surnames.

The study presented an alternative scenario based on a 2022 survey by the Japanese Trade Union Confederation, in which 39.3% of 1,000 employees aged 20 to 59 said they would prefer to share a surname even if they had the option of using separate ones.

Under these circumstances, Yoshida, whose study was commissioned by the Think Name Project and other organisations advocating for the legalisation of choosing one's surname, projected that by 2531, only 7.96% of the Japanese population would have the surname Sato, as reported by the Mainichi Shimbun.

Groups advocating for a change in the law regarding married surnames hope that their campaign will gain momentum from the prospect that surnames like Suzuki, Watanabe, and even Yoshida – the 11th most common surname – could one day disappear.

While the government has allowed maiden names to be used alongside married names on passports, driving licences, and residence certificates, Japan remains the only country in the world that requires spouses to use the same surname.

Conservative members of the ruling Liberal Democratic Party (LDP) argue that changing the law would "undermine" family unity and confuse children.