• Dr. I. J. Good; "The Human Preserve"; Spaceflight 7 (September 1965):167-170 (note that this is the magazine published by the British Interplanetary Society, ISSN 0038-6340; they don't sell back-issues that far, don't appear to have been scanned by IA or Google Books, and only seems to be available through universities with print collections that far back like UWash)

In The Many Worlds of Hugh Everett, there's an interesting endnote:

Good and Everett were acquainted: both did work for IDA’s communications division in Princeton (probably cryptographic tasks for the National Security Agency). Among Everett’s papers is a copy of a treatise by Good called “The Human Preserve.” It speculates that our galaxy is secretly governed by telepathic “Chief Entities” who preserve inter-stellar law and order in what amounts to a galactic zoo. Good said that self-replicating intelligent machines would long ago have taken over the zoo were it not for intervention by the Chief Entities, whose beneficent occupation saves us from descending into anarchy. The analogy between guardianship by the Chief Entities and the American national security state’s promotion of its role as a “global policeman” was intentional.

We're all familiar with his essay on superintelligent machines, and it seems this links up.