It's entirely a human concept
I am sorry, there is no polite way to say this: Oh ye gods of basic education, that's utter nonsense. Evolutionary principles work across all of time and space. They (would) apply to Thargoids just as they apply to any other life form. Either they are able to increase their numbers, or they go extinct, in which case they couldn't (COULDN'T) have evolved in the first place.