For many long-time science fiction readers, the TV series Firefly "clicked" immediately, unlike most television* (and even cinematic) SF.
At least, it did for me, and it was only recently that I realized why. The universe of Firefly is a very familiar one, with deep antecedents in age-of-Campbell SF. H. Beam Piper's Terro-Human Future History neatly brackets the series, with a central government ("Terran Federation" rather than "Alliance" but both including a Parliament) and a war of consolidation (Piper's "System States War" vs. the "Unification War") and the events in Firefly occurring after the war but before The Cosmic Computer.
While Piper's fictional stage-setting includes faster-than-light travel and Whedon's does not, travel times are comparable, as are the range of planetary cultures and their socioeconomic variations, both internal and external.
...But it's not just Piper; the Serenity's own work niche was greatly presaged in Andre Norton's novels of the Free Trader Solar Queen, one of many independent traders operating at the fringes of an interstellar civilization, often in conflict with large, corporate ventures (Blue Sun, anyone?).
Piper and Norton served as a template for many SF works to follow; thus parallels and echoes can be found in the work of C. J. Cherryh, Lois McMaster Bujold, Greg Bear and many others -- a company into which Firefly fits quite comfortably. You cannot say the same of much SF on the large or small screen; Babylon 5 was, in its better moments, Cherryh-esque, but without any dust in the corners or broken pipes.
Whedon, corny-Western dialog and all, managed to tap into a nice corner of SF turf without leaving muddy bootprints; he and his writers may not have realized exactly what they were doing, but they were clever enough to play it as they found it.
* Star Trek, for example, is very much its own self-contained thing, a TV (and later film) drama that merely happens to take place in a far future framework -- and that's not to fault it, that's what it set out to be; Gene Roddenberry described TOS as "Wagon Train to the stars." But it has weak ties to SF's own history as a result.
5 weeks ago