In the distant future, humanity has spread among the stars.
Earth, that ancient green gem, has been long since left behind, and now most humans are a spreading wave of habitat ships, trundling through the depths of space from one star system to another.
When a habitat ship arrives, it gathers the easily accessible resources of that star system, builds itself bigger, and then wanders off to another star, travelling for another century or two.
But it is not the ability of the habitat ships to gather resources or to build that define this long era of human history, but rather that they can reorganize to split themselves into two or more habitat ships.
In this way, humans once again have the all-important ability to leave.
Anyone who is dissatisfied or disagrees with the way things are run on a habitat ship is free to leave with any like-minded individuals. They can ask the ship to split, and the ship will rebuild itself to become two smaller independent habitat ships, both capable of sustaining their human cargo in the same fully automated luxury that most people prefer.
This has led to a wild diversity of human cultures, human thought, human moralities, human... well, everything. Ideologies so incompatible that they would normally incite violence simply choose different directions in the infinite blackness of space, wandering along at relativistic speeds.
After thousands of generations worth of ships splitting apart, every possible creed, every possible variation, every possible variation on humanity is represented out there in the universe.
--
By its nature, this is not a way of life that is always maintained by those who practice it. Some offshoots of habitat ships choose to stop in star systems, descend deep into the gravity wells, and build whatever they choose. It is not a fast process to, say, convert a binary star system into a star and a ringworld, but that's what stasis is for, or perhaps sending some machines ahead of the habitat ship. (None of the Alderson Disk projects have quite finished, but the machines continue to churn away.)
This has thus had the effect of also seeding star systems with life, but the ever-expanding frontier of human life continues in all directions at nearly the speed of light, and--to those who live in the habitat ships--the best meta-civilization that has ever existed.
(I mean, otherwise they wouldn't be out there, right?)
