l remember many elders speculating that once the earth is full theres a chance mankind may go on to inhabit the rest of the universe.
I may be wrong but I do think that was speculated in one of their publications at one time .
And the reasons put forward then was that the planets are in different stages of being prepared for human habitation .
Or something along those lines .Most likely it was stated between the 60`s - 80`s time frame.