True, but we have a lot of evidence of Earth and it's history of life, and basically no evidence of alien worlds. So we are warranted in being more certain about our beliefs about Earth.Agreed on both points.
The preponderance of evidence indicates that we're the only ones we know about. Likewise, we can either surmise that humans are the only technologically capable, intelligent sentient species in the Universe based upon the preponderance of evidence, or we can surmise we're the only ones we know about.
I respect that you put stock in the red Queen hypothesis.Agreed about the resilience of more primitive lifeforms, I'm still inclined to the Red Queen hypothesis that intelligence and sentience are the inevitable consequence of species survival for both predator and prey.
That said, due to the vast distances involved and the unlikely probability that life will generate, we might be the only lifeforms in our galaxy. Out of the two trillion+ galaxies in the Universe, that's still a lot of eventual sentient species.
That deals with evolution by natural selection and genetics.
The first hurdle to get over is the origin of life itself. We have made barely any progress in the last 70 years in understanding how biology somehow emerges from inanimate chemistry.
The cockroaches will still be here long after homo sapiens are extinct and gone. So if nature has an ideal blueprint for a successful and resilient species, it doesn't seem to be a bipedal hominid with a large brain.
Agreed on the exceptional rarity of life.