In all cultures, some names are more popular than others. But in Japan, this may reach a whole new level because couples are forced to take the same name. Hiroshi Yoshida, a professor of economy at Tohoku University, carried out a simulation of how one particular name (Sato) could become more and more popular. Although the study is not entirely serious (it’s meant to campaign against the name law), it shows how one surname could overtake the others.

A country with just one name

In Japan, married couples have to share the same surname. In theory, the couple may take either name, but in practice, over 95% of couples adopt the male surname. Together with Japan’s demographic trends, this policy has contributed to the dominance of certain surnames, like Sato. Yoshida’s simulation humorously predicts that if current trends continue unchecked, a significant portion of Japan’s population could end up sharing this common surname, highlighting the peculiarities of current societal norms.

Already, 1.6% of the people in Japan are called “Sato” — and that figure is slowly growing. Yoshida’s models start from the past two years — a very limited dataset — and project what will happen in the future if current trends continue. According to their model, by 2446, over half of all Japanese people would share the same surname.

It is important to note that it is typical and polite in Japanese culture to refer to people by their family names. So, by 2531, everyone would be called “Sato.”

“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.”

Of course, this isn’t a comprehensive calculation. Immigration and many other social aspects could get involved and change the numbers. The study is meant to raise awareness of the implications of not mandating a law that requires couples to have the same surname. However, there’s a clear warning in the research as well. Unlike given names, which rise and wane in popularity, surnames are “stickier”: once you have one, you’re stuck with it.

Aside from leading to some bizarre social situations, Yoshida also sees another problem: the history of other family names is being erased in this process.

“Considering that a family name has a family history and is also a cultural symbol, its loss would mean that the history of the family name would also cease to exist,” Yoshida said in a statement.

“Personally, I see changing one’s name as a separate issue from getting married and living with one’s partner. If we value individuality even more, there is no necessity to change one’s name upon marriage,” he added.

Changing the law

In other countries, couples aren’t forced to take the same name, which leads to less homogenized names. In Japan, over 5% of the country’s population shares just four surnames: Sato, Suzuki, Takahashi, and Tanaka.

The government now allows maiden names to appear alongside the married name on passports and other ID, but Japan is virtually the only country in the world that legally requires spouses to use the same name.

The ruling Liberal Democratic party (a conservative party) rejects this change in name policy as they say it would “undermine” family unity and cause confusion among children.

However, Japan’s demographics has bigger problems than this. According to recent estimates, the country’s population is set to decline by about 30% by 2070, in part due to its rejection of large-scale immigration. Japan has long been known for its steadfast refusal of immigration, although that may change, particularly due to demographic pressure.

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