Everyone in Japan might have the name “Sato” in 500 years, professor cautions

In all cultures, some names are more popular than others. But in Japan, this may reach a new level because couples are required to have the same last name. Hiroshi Yoshida, an economy professor at Tohoku University, conducted a simulation to show how one particular name (Sato) could become increasingly popular. Although the study is not entirely serious (it’s meant to protest the name law), it demonstrates how one surname could surpass the others.

A country with just one name

In Japan, married couples must share the same last name. In theory, the couple may choose either name, but in practice, over 95% of couples adopt the male surname. Along with Japan’s demographic trends, this policy has contributed to the dominance of certain surnames, such as 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.

Currently, 1.6% of the people in Japan are named “Sato” — and that number is gradually increasing. 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 last name.

It is important to note that it is customary 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 last name. 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 last names: 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 governing party, the Liberal Democratic party (a conservative party), opposes the name policy change, stating that it would disrupt family unity and confuse children.

But Japan's population issues are more significant than this. Recent estimates suggest that the country's population is projected to decrease by approximately 30% by 2070, partly because of its refusal of large-scale immigration. Japan has been known for firmly rejecting immigration, although this may change, especially due to demographic pressures.

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