Simak has been called a pastoral writer, a stronghold of old USA communal values. In contrast with other more pessimistic SF writers, he should be a good all american farming boy. Many SF tales of those years (40-60 of the 20th century)are optimistic and show a great confidence on the capabilities of humans and technical progress.
Nevertheless, this novel is far from that: he portraits a world in which technology has made Earth useless, the struggle for life is over, and so society falls apart. Through succesive generations of a family (all of them fail their high mission) he describes Earth's decay: first society as such, then the planet itself is abandoned for Mars or Jupiter where men become Jovians, a more gifted race, then the last humans go back to the stone ages. Only robots and gentically modified and speaking dogs stay behind to prepare a better future to those men, a task which seems nearly doomed to failure due to our intrinsic violence. On the other side, some of those misfits left behind turn into mutants with extraordinary mental powers (telepathy, superior intelligence, extravagant whims) and create a new breed of ants which in their turn take the same menacing trait as men.
Dogs and the last of the robots are left to wonder what could be, what will be...
Not all together an optimistic tale. There are robots, there are stars, but Simak is not Asimov and there's not a happy ending but a melancholic one.