Ancient Astronauts: Almost certainly happened in at least a few times and places, for the same the-Galaxy-is-old-and-relatively-life-rich reasons that are why half the systems in it are practically knee-deep in elder-race trash.

Also, technically, connected with the origins of the eldrae and greenlife in general from prehistoric Earth, although given that Earth is not found and not likely to be in canon, no-one has a clue where those fossils of so-called Pseudoeldrae archaea came from, or exactly what they have to do with anything anyway, even if we’d clearly recognize an offshoot of genus Homo if we saw one.

Averted in the “alien abduction” meme sense, just because, as mentioned, lighthuggers ain’t that subtle.