The movie's thematic is heavily based on cycles. There are a lot of things that paradoxically come to existence out of nowhere and close a cycle, a loophole. Like Cooper sending himself to the Nasa base, and future super humans creating the wormhole to save themselves in the past.

So I think there is one more hidden cycle. The clue: old Murph's words at the end are: "Brand, she's out there (...) by the light of our new sun, in our new home (...)"

What if we took the meaning of the word "new" as "young"?

The planet that Brand landed on is actually the Earth, in it's early days, millions of years ago.
The worm hole actually leads to the same solar system as our own, but millions of years in the past.
The human race is closing a cycle: they are going to the past to populate their own young Earth. They are they're own creation.

In the past of our own Earth, they prospered and managed to evolve into the super humans that eventually created the worm hole to close their own cycle and save their ancestrals (us).

You would have to believe that some event untold in the movie happened to explain why there are no super humans in the present day at the Earth. Maybe the advanced humans left the Earth for some better planet, or moved into a new universe, or all of the advanced humans died due to some catastrophe, whatever, use your imagination. But the cavemen (ancestrors of the homo sapiens race) are they breed, and they stayed in the Earth and managed to evolve into us, closing the cycle.

There is a book and documentary called "The Chariots Of The Gods" by Erich von Däniken, which is quite famous and probably known by Nolan. In some languages it was released with a title that would translate to english as "Were the Gods Astronauts?". It expresses the author's belief that the Earth was visited by alien astronauts in the past. It connects well with this hidden plot in Interstellar.

One could argue that the early Earth would never be as habitable as Brand's planet, and the other planets in our solar system could never look like those other planets seen in the movie. But hey, it's science fiction, maybe they could have been like that in the past in the movie's universe.

And about the Gargantua? We never had a black hole near our solar system. But maybe it was created just to attract Cooper into Murph's 4-dimensional room, and was deleted by the super humans just after Cooper was released near Saturn.

ancient astronaut theory. we are the ancient astronauts to Brand's planet's future. and any bacteria that came from us that landed on any of those 11 other planets could, one day, sprout into greater life on those planets. thus making us the ancient astronauts on any/all of the 12.