The polishing happened in two steps. Around 1923 the English music-hall and radio comedian John Foster Hall (1867–1945), performing as “The Revd. Vivian Foster, the Vicar of Mirth,” put it in an adult’s mouth on the record The Parson Addresses His Flock: “We are all here on earth to help others; what on earth the others are here for, I don’t know.” The children are gone; the pulpit does the work.
Three years later a second polish produced the version on this page. Lord Dewar, by then a professional dinner-table wit, was reported delivering it as one epigram among several — “Hope is the undergarment of optimism,” “Life is full of trials, with an occasional conviction.” The tighter, first-person “I often wonder” construction is the one that stuck on quote sites.
Auden comes last, and he comes as a reader. He dropped Foster Hall’s wording into his 1942 essay on Bernard Shaw as a parenthetical aside, and used it again in 1948 in “Squares and Oblongs.” Edward Mendelson notes that Auden never claimed credit for it — but a famous name attached to a good line is hard to detach, and the real source stayed unknown to Auden scholars until a 2002 letter in The Spectator identified it.