The sins of their fathers: Illegitimacy in Japan and surrogate punishment across generations

In late 2013, the Japanese Supreme Court voided inheritance rules giving non-marital children half the shares of their marital half-siblings. To discriminate against non-marital children was to punish them for the sins of their parents, it explained, and doing so violated the equal protection clause of the Constitution. In fact, however, the inheritance rules had reflected a simple selection bias – much like the stigma that traditional societies routinely attached to illegitimacy: The societies that survived were those where more children lived to reproductive age; in harsh environments (the norm until a few centuries ago) whether children survived turned on the level of investment adults made in them; men tend not to invest in children whose paternity they do not know; hence, non-marital children had been substantially less likely to survive. In such a world, the stigma and disabilities attached to illegitimacy had helped minimize the number of non-surviving children by channeling sex into stable dyadic relationships. The earlier Japanese inheritance rule had promoted that relational stability by helping women hold men to their promises. In order to induce women to marry them, men routinely promise to invest in the children they bear together. The pre-2013 rule had assured women that if their husbands breached those promises in life, they could at least trust the law to favor their children in his death. On the strength of those promises, they had married and bore children within marriage. After 2013, the courts no longer offered them that assurance. Keywords: inheritance law, non-marital intestate shares, surrogate punishment, marital capital, evolutionary biology