The simulation showed that by 2531, all Japanese will have the same last name

Japanese scientist Hiroshi Yoshida conducted a simulation that showed that by 2531, every Japanese citizen will have the last name Sato, The Register reports.

Currently, it is the most popular last name in Japan: more than 1.5% of Japanese people are proud to bear it, slightly ahead of the Suzuki last name.

However, Japan has relatively few last names for such a large population. It is estimated that the top ten most popular Japanese last names cover 10% of the country’s population.

Professor Hiroshi Yoshida of the Research Center for Economics and Society of the Elderly at Tohoku University used open-source information – collected from government statistics and phone books – to determine that the last name Sato increased its prevalence by 1.0083 times between 2022 and 2023.

He then assumed a constant growth rate to calculate how quickly the most popular last name would spread to the entire population. He also took into account the country’s population growth projections.

Yoshida found out that by 2446, more than half of Japan’s population would bear the last name Sato. And by 2531, everyone will have this surname.

This exercise was intended to promote changes in Japan’s civil code, which requires married couples to have the same last name.

If Japan rethinks its policy, it is projected that by 2531, less than 8% of the population will bear the Sato last name. However, this last name will still become the predominant one – it just won’t happen until 3310.

To arrive at this conclusion, Yoshida assumed that 39.3% of the population would share a common last name after marriage, according to a survey conducted by the Japan Trade Union Confederation in 2022 of single people who would like to share a common last name.

However, the simulation also made it clear that in 3310 this will not be a big problem because, given the rate of birth decline, Japan’s population will number only 22 people by then.

The study was published by the Think Name Project, an organization that advocates for allowing couples to decide whether or not to change their last names.

Japan is the only country in the world where married couples must have the same last name, the organization says. And while couples can choose any surname when they get married, statistics show that men keep their last name and about 95% of women take their husband’s last name.