In Poul Anderson's "Genesis," the whole galaxy is coalescing into a sort of brain comprised of hugely intelligent "nodes." The node on Earth has broken contact with the rest of the galactic brain. A secret agent in human form investigates and learns that the Earth node is carrying out strange experiments on human civilizations--both "real" humans struggling to survive and "virtual" humans endlessly replaying variations on key events in human history.

Published in Far Futures. Reprinted in The Year's Best Science Fiction: Thirteenth Annual Collection.