Imagine a scholar sets out to find the one moral principle that every major civilization in human history has independently arrived at — not through contact or borrowing, but through its own philosophical and religious reflection. The principle that appears in ancient China and ancient India, in the Hebrew scriptures and the Christian Gospels, in Islam and Confucianism and Buddhism and Stoicism and Kantian ethics. Is there such a principle?

There is. Treat others as you would wish to be treated. Do not do to others what you would not want done to you. In one form or another, the Golden Rule appears in virtually every major ethical and religious tradition humanity has ever produced — across thousands of years and thousands of miles of cultural separation, arrived at independently, again and again.

That convergence is philosophically ex ...