ALL JAPANESE WILL BE NAMED "SATO" BY 2531

A Japanese Professor has claimed that all Japanese people will have the same family name by the year 2531. This is because more common family names have an inbuilt statistical survivability advantage over rare family names.

As reported by the Mainichi Shimbun:

"All Japanese people will have the last name 'Sato' by the year 2531 if the country continues to require couples to choose either the husband's or wife's last name upon marriage, a simulation by a Tohoku University research center has shown.

According to the study leader, Professor Hiroshi Yoshida at Tohoku University's Research Center for Aged Economy and Society, Sato is the most common last name in Japan, had by 1.529% of Japanese people as of 2023. He calculated two scenarios -- one where Japan maintains the single surname system among married couples and the other where the country introduces a selective, separate surname system.

Yoshida used data available at the website Myoji-yurai.net, which provides name-related information such as common last name rankings based on government statistics and phone books. Based on trends in the number of people with the surname Sato, Yoshida calculated the proportion of the Japanese population with this last name and estimated growth rate.

Yoshida's calculations showed that, under the current system where the husband or wife change to share the same surname, the proportion of the Japanese population with the surname Sato increased 1.0083 times from 2022 to 2023.

Assuming the growth rate remains constant and couples named Mr. and Mrs. Sato continue to increase every year, more than half of the population will be named Sato by year 2446, increasing to include everyone by 2531."

The reason for this tendency can be simply explained. Even if we assume a fertility flatline where every couple has exactly two children, a surname that is held by only one married couple has a 33% chance of becoming extinct every generation due to women taking the names of their husbands, because that couple could only have two daughters, two sons, or one of each, In the case of two daughters the name would become extinct.

From a video showing how the surname "Sato" is increasing

The more common a surname is, the less vulnerable it is to this statistical bias, but all surnames have a tendency to decrease relative to the more common surnames. As Sato is the most common surname it will continue to gain in numbers relative to other Japanese surnames unless other factors intervene.