I wonder if the great filter is not one, but multiple coincidences brought upon by "intelligent" life and the natural lifetime of a planet and/or solar system. If Mars had intelligent life and now it doesn't how does that bode for Earthlings? Can life really adapt given the lack of evidence anywhere? I wonder how will space travel to the next possible habitable planets work. Shoot in all directions and hope that life…
It would not surprise me if civilizations evolved in the same way life did on Earth. Life evolved in the sea. At some point life evolved to leave the sea and go to land, whether the sea was no longer hospitable enough, or in search of better food. Life continued to evolve on Land, specializing into different groups and colonizing different lands. Perhaps civilizations evolve on their planet, then at some point they l…
The most probable scenario is that life is born multiple times, in multiple places, when conditions permit it.
There's no evidence of life moving across planets of different star systems.