Surname Extinction Simulation
A multi-agent simulation modeling the extinction and convergence of Japanese surnames
In Japan, new surnames are virtually never created, and married couples are legally required to share a single surname. Under these rules, surname diversity can only decrease over time, which means probabilistically, everyone will eventually converge to one. But how long would it take for the entire population to converge into just a single surname?
I built a basic multi-agent simulation starting from Japan’s current ~300,000 unique surnames to track their extinction and eventual convergence.
Generational Convergence
Simulating random pairing across generations and tracking surname inheritance revealed a distinct decay curve:
- Rapid Early Extinction: Within the first few thousand generations, rare surnames vanish at an alarming rate, plummeting from 300,000 down to tens of thousands.
- The Long Tail: As the pool shrinks, the rate of loss slows into an extremely long tail, ultimately converging into a single remaining surname after roughly 500 billion years (over 1.5 million generations).
An agent-based modeling experiment taking the mathematical reality of surname inheritance laws to its logical extreme.