The Evolution Of Future Histories

Extrasolar colonists and interstellar traders are complementary, not contradictory. Thus, James Blish's Okies could have traded with his Adapted Men. However, the logic of the pantropy series took it into a remote future when Earth had changed enough to be recolonized by Adapted Men whereas the logic of the Okies with their antiagathics had some of them surviving until the end of the universe which, for narrative purposes, came sooner than expected with a cosmic collision. The two series, having acquired incompatible endings, also acquired different although parallel beginnings. References to Oc dollars, the ultraphone and "gods of all stars" in The Seedling Stars suggest a stage in their composition when the two series could have been one.

Poul Anderson's Technic History features a Terran Empire ruled from Archopolis whereas both his "The Star Plunderer" and his "The Chapter Ends" refer to a First Empire ruled from Sol City. However, "The Star Plunderer" became a pivotal story in the Technic History whereas "The Chapter Ends" became the culmination of the Psychotechnic History.

In Robert Heinlein's works, Dahlquist, the Space Patrol, Rhysling, a Stone Family in Luna City and particular versions of Martians and Venerians link five early Scribner Juveniles to The Green Hills Of Earth, Volume II of the Future History, but the Juveniles are incompatible with the Future History as a whole. Thus, Heinlein wrote what I call a Juvenile Future History.

So far, this post has referred to three sf authors each writing two future histories but the real situation is more complicated. Anderson wrote several future histories (see here). Blish gave his Okies the instantaneous Dirac communicator but then had to develop the full implications of this communicator in a third future history. My advice: read them all.