Early in his book, Professor MacAskill considers the provocative hypothesisthat the best man ever to have lived was a Ukrainian named Viktor Zhdanov. Working with the World Health Organization, Mr. Zhdanov called for a systematic campaign to eradicate smallpox. He presented a visionary plan, sold the organization on the idea and, by accelerating the end of smallpox, probably saved many millions of lives. If you haven’t heard of him, or haven’t thought of him lately, that’s evidence that the effective-altruism movement has something to offer. Even for small givers, a more rational approach to philanthropy can focus attention on areas that make the biggest enduring contribution to human welfare.