In Foundation, the galaxy is populated by only one type of life form: humans. Analomies have sprung up, like mutants and genetically enginered hemaphrodites, but there are no true aliens. One very important fact pointed out in the last book in the Foundation series, is that this peace and serenity may not last. On the world of Gaia, another seed had been planted a long time ago, as an alternative to the Foundation. Now they rise up, ready to transform the galaxy into one being, Galaxia. The purpose of this is the same as the government that the Foundation has been creating: to make humankind more stable, to become a better race of beings. Yet they are not sure that they are doing the right thing. They call on Golan Trevize, who has the ability to tell what is "right", to help them decide. He decides on Galaxia, on the slow process of creating the galaxy as one superbeing. But he doesn't know why. He searches throughout the entire last book, and finds the answer on the moon of Earth: If an invading force from another galaxy comes, they will invietably turn humans against humans. If humankind is one living organism, a. k. a. Galaxia, this is impossible, as the galaxy will act as one, driving these invaders away. Unfortunately, we never get to see what happens, even though Asimov leaves us with a very suspensful ending. The reason for this is simple: the author passed away.