One thing that gives me pause for thought: even here on Earth, we are all, likely, descendants of a single organism: https://en.wikipedia.org/wiki/Last_universa

One thing that gives me pause for thought: even here on Earth, we are all, likely, descendants of a single organism: https://en.wikipedia.org/wiki/Last_universal_common_ancestor https://en.wikipedia.org/wiki/Last_universal_common_ancestor . It doesn't necessarily mean that the 0-1 creation of life happened exactly once on Earth (maybe it happened many times but the other lineages died out), but I think it makes this argument likely. We see a near-infinite menagerie of different organisms, from archaea and bacteria to reptiles and mammals, each finding its own niche, yet we don't see, on our own planet, any other blueprint for 0-1 life creation. Everything is DNA/RNA and cells, based on carbon and water, etc. And here we know conditions are just right, and we have studied the Earth like no other alien world. I'd expect, if the universe is in fact teaming with life, that we would see "aliens" on our own planet. But all we see is descendants of LUCA. It seems to me that either "life" is in fact vanishingly rare, or there's lots of other life forms we don't notice (including on Earth). My gut feeling is on the former.