Imagine shouting, ‘Hey, Sato!’ and every Japanese person turns to look. Statistical modeling suggests that, under current laws, every resident of Japan could end up with that surname.
This is because, under Japan’s Civil Code, which has been in effect since the late 19th century, married couples are required to share a single surname. Japan is the only country in the world that enforces this rule. Professor Hiroshi Yoshida of the Aging Research Center at Tohoku University warns that, if the law doesn’t change, in about 500 years every Japanese citizen could have the surname Sato. If that happens, people would have to use given names or numbers to tell each other apart. Yoshida says that’s not an acceptable outcome.
In 2023, Sato was the most popular surname in Japan, accounting for 1.529 percent of the entire population. At first glance, that doesn’t seem like much. However, Yoshida says that because of the odds, many marriages involve partners who already share the most common surname. If this trend continues, Sato could overshadow all other surnames, as reported by IFLScience.
However, if Japan changes the law, by 2531 only 7.96 percent of citizens would have the surname Sato—assuming 39.3 percent continue to choose it—according to a 2022 survey.
But there’s a catch. The predictions from Tohoku University may not come to pass because Japan’s population is rapidly declining. Currently, it stands at about 126 million people. According to the ‘Future Population Projections for Japan,’ by 2120 the population is expected to drop to 41,229,000. If this trend continues, by 2531 Japan will have only 281,866 residents, and by 3310 just 22 inhabitants.
In other words, even if the forecast of a single surname dominating the country is pushed back by 800 years, Yoshida warns there is a high probability that the Japanese population could shrink to extinction before that happens due to declining birth rates.
His team conducted the research at the request of the Think Name Project, which aims to pass a new law that would allow spouses to keep different surnames.
The second most common surname in Japan is Suzuki.
