Everyone in Japan will be called Sato by the year 2531 because of the country's marriage laws

In 500 years, everyone in Japan will have the surname Sato thanks to the country's current marriage laws.

If the practice of requiring married couples to share the same last name - instead of retaining their birth names - continues in Japan, there may be no other surname left by the year 2531.

Japan is the only country in the world that requires spouses to use the same last name, following an archaic civil code from 1898.

As of 2023 the most common last name in Japan was Sato, accounting for around 1.5 per cent of the country's population.

A Tohoku University economics professor, Hiroshi Yoshida, has forecasted that if this continues, the only surname left will be Sato which will inevitably lead to social chaos.

The scenario would see every sports team, classroom, and office referred to as Sato-san.

But this result would be a product of Japan's marriage laws which state that Japanese people who marry must adopt the surname of one or the other of them.

In 95 per cent of cases, this means that women give up their maiden names and taken on the name of their husbands.

Around 500,000 new marriages are registered a year in Japan, meaning that almost half a million people lose their surnames per annum.

The annual growth rate of Sato is reportedly increasing by 1.0083 per cent according to date collected between 2022 and 2023. 

In Japan, over 5% of the country’s population shares just four surnames: Sato, Suzuki, Takahashi, and Tanaka. 

If no changes are made to the current legislation, the hypothesis suggests 50 percent of family names will be Sato by 2246.

A series of legal challenges have failed to overturn the marriage laws seen in today's Japan, even after several complaints have been put forward highlighting that they disadvantage women who have built their careers under their maiden name.

Until Yoshida's study, however, none had fully recognised the seemingly unstoppable rise of Sato - and the consequences its takeover could have on society.

Yoshida told Japanese Newspaper, The Mainichi: '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 good world to live in.'

A country full of Satos 'will not only be inconvenient but also undermine individual dignity,' he said in an interview with Japanese newspaper Asahi Shimbun.

'This would also lead to the loss of family and regional heritage associated with surnames.'

The study, using data from the Japanese Trade and Union Confederation in 2022, also revealed that if different surnames were allowed it would delay the possibility of one dominant name to 7.96% by 2531.

But they suggest that due to the declining birth rate it is predicted the Japanese population will be extinct by then.

The study was supported by the Think Name Project, a group advocating for a change in the selective separate surname system. 

Groups calling for change in the law on married surnames hope their campaign will receive a boost from the possibility that names such as Suzuki and Yoshida - the 11th most common name - could one day be wiped out.

Yoshida's study was reported on Monday, and many assumed it was an April Fool's Day prank, but the professor said he wanted to give people pause for thought on the shocking - but very possible - scenario.