Most adoptions in Japan are not of children but of grown men in their 20s and 30s, tens of thousands of them a year, because families that run businesses legally adopt a promising employee or son-in-law as heir, a succession practice that has kept some firms under one family name for centuries

Japan has one of the highest adoption rates on Earth — on the order of 80,000 adoptions a year, second only to the United States.

Almost none of them involve children.

By the most-cited accounts, the overwhelming majority of Japan’s adoptees — over 90 percent, some analyses say 98 — are adult men in their 20s and 30s. Grown professionals with degrees, careers and, until the paperwork clears, their own surnames.

They are not being rescued. They are being recruited.

The heir problem, solved with a pen

The practice is called yōshi-engumi — adoption of an heir — and its most famous form is the mukoyōshi, the adopted son-in-law.

The logic descends from Japan’s old household system. Under the prewar civil code, family wealth and headship passed down the male line, traditionally to the eldest son. A family that ran a business but produced only daughters — or produced a son with no aptitude for the ledger — faced the extinction of its name and firm in one generation.

The fix was elegant and legal: find a capable young man, marry him to a daughter, and adopt him. He takes the family surname, enters the family register, and becomes, in law, a son — first in line for the shop, the sake brewery, the bank. As one Japanese sociologist put it, it was a very pragmatic decision for the family business to survive. A Japanese proverb states the strategy outright: better to have daughters than sons, because then you can choose your sons.

The prewar inheritance rules are long gone. The practice is not. Adult adoption in Japan today requires little more than consent and a registration form — it is legally easier than adopting a child, which needs court approval.

The firms that refuse to die

The results are visible in the world’s corporate longevity tables, which Japan dominates to an almost absurd degree.

The oldest companies on Earth are disproportionately Japanese: construction firm Kongō Gumi, founded in 578 and family-run for some 1,400 years; inns and breweries counting 40-plus generations. Japan has centuries-old firms by the hundred, and adult adoption is one of the quiet mechanisms underneath — when the bloodline failed to produce a manager, the family simply adopted one, and the name on the door never changed.

Nor is it only small firms. Some of Japan’s most recognizable business dynasties have passed through adopted heirs at one point or another: Suzuki’s longtime chairman Osamu Suzuki was himself a mukoyōshi — the fourth adopted son in a row to run the company. Toyota, Canon and Kikkoman family lines have used the practice. There are matchmaking services and dating sites specifically for men hoping to be adopted by heirless business families, some advertising the arrangement’s considerable upside: a bride, a surname and a company.

The economics of chosen sons

Here is where the custom stops being a curiosity and becomes a management finding.

A landmark study in the Journal of Financial Economics — analyzing decades of Japanese firms — found that companies run by adopted heirs were “puzzlingly competitive”: they outperformed not only firms run by blood heirs but, on some measures, professionally managed non-family firms too.

The researchers’ explanation has two blades. First, adoption lets a family pick its successor from the entire population of talented men rather than the genetic lottery of its own children — displacing what Andrew Carnegie once called the deadened talents of inherited wealth. Second, the mere possibility of adoption disciplines everyone: biological sons who know they can be passed over for a star employee work harder, and ambitious managers stay at family firms where the top job is genuinely winnable, by marriage and paperwork if necessary.

Family control, the study concluded, can cause good performance — but partly because in Japan, “family” is a decision.

The asterisks, and the point

The honest footnotes: the 80,000 figure includes adoptions done partly for inheritance-tax planning, since each additional legal child raises the tax-free allowance — one Diet member estimated in the 1980s that nearly every wealthy estate added an adoptee or two. And the tradition sits oddly against modern norms; the adopted groom takes his wife’s name in a country where that remains rare, and commentators note the psychological weight of trading one’s surname for a company.

But the core of the practice is exactly what the title says, and it is a genuinely different answer to a universal problem. Every family firm on Earth eventually faces the succession question, and most solve it by hoping the next generation is up to it. Japan’s business families declined to leave it to hope. For centuries, when the heir wasn’t born, they signed one — and the companies that outlived empires, wars and every rival economy’s dynasties did it, in part, because in Japan a family tree can be edited by a notary.