If something only happened once in our planet’s history, without which we wouldn’t be here, then that doesn’t tell us about how likely it is (anthropic reasoning, we’re only on the planets where it happened). If it happened multiple times on a single planet, then it can’t be TOO unlikely, and probably common enough that a significant fraction of planets with prokaryotic cells anything like ours will eventually end up with eukaryotic cells.
It’s the same kind of argument as if we found life that independently evolved on another world in our own solar system. If life evolved twice independently on two adjacent planets even though those planets differ in significant ways (number and size of moons, geologic history, temperature, light exposure) then abiogenesis must be common enough that it happens on a substantial fraction of all planets, and can’t be the reason we don’t see lots of other civilizations nearby.
If something only happened once in our planet’s history, without which we wouldn’t be here, then that doesn’t tell us about how likely it is (anthropic reasoning, we’re only on the planets where it happened). If it happened multiple times on a single planet, then it can’t be TOO unlikely, and probably common enough that a significant fraction of planets with prokaryotic cells anything like ours will eventually end up with eukaryotic cells.
It’s the same kind of argument as if we found life that independently evolved on another world in our own solar system. If life evolved twice independently on two adjacent planets even though those planets differ in significant ways (number and size of moons, geologic history, temperature, light exposure) then abiogenesis must be common enough that it happens on a substantial fraction of all planets, and can’t be the reason we don’t see lots of other civilizations nearby.