Geek alert: my theory on how humans colonised the Star Wars Galaxy.

Which is basically that, at some hypothetical point in our future, a group of (post-human? Sith?) Force-sensitive individuals (for reasons of their own, good or evil) basically manipulated organic matter on hundreds (or thousands) of worlds, in thousands of different time periods, making them both habitable for humans and, more importantly, making certain that humans would emerge, probably fully grown, a la the "Pod People" (Invasion of the Body Snatchers) on these worlds.

Of course, as one interpretation of Special Relativity states that one travelling faster than light will also back in time, then the further on travels in space, the further back one would travel in time.

Being further back in time, by either method, would allow for (ironically) higher human populations the further away from Earth you went simply due to the extra time a planetary population would have to grow to its natural limits.