An important nuance here is that LUCA doesn't really imply there was only that one organism. There could be more organisms, it's just the one that we can trace,

An important nuance here is that LUCA doesn't really imply there was only that one organism. There could be more organisms, it's just the one that we can trace, similar to mitochondrial Eve (see the "popular reception" section): https://en.m.wikipedia.org/wiki/Mitochondrial_Eve https://en.m.wikipedia.org/wiki/Mitochondrial_Eve