How is intelligent alien life explained in Alien (1979) and Aliens (1986)?

Basically the title, since it seems in both movies they don’t bat an eye at “derelict alien ship”, which seems to indicate it’s not a novel concept or somehow not surprising?The “mom and pop survey team” casually discovers what appears to be a non-human ship and don’t hesitate going in?Also, the marine platoon complains about the mission being “another bug hunt” during the briefing on the Sulaco, so non-intelligent alien life is pretty much a given?I’m asking specifically about the two movies since Prometheus retcons the Engineers / Builders into the lore.LE: Some of the comments made me think / revisit Aliens (1986), here are some clues: - early in the movie the marines mention "Arcturian poontang", it stands to reason that species would be at least at the human level of intelligence (hopefully...)the platoon is hoping for a "stand up fight" instead of "another bug hunt", which I see as them having routinely faced off against non / less intelligent life forms in the defense of Earth's space colonial interests; some comments think of "bug hunt" as rebels, but I find it unlikelyRipley states getting the organism past "ICC quarantine would be impossible" and in the same scene Burke mentions "the rights to it would be worth millions to the company's bio-weapons division"; this would indicate there is a plethora of alien life for such a division to exist as well as for quarantine procedures to be in place for protection and / or as result of previous exposure;there is a line at the hearing at the start of the movie when the smoking lady says they've not seen "anything like this in over 300 surveyed worlds", which can also be interpreted as having found life on those worlds, but not threatening to humans or not such an exotic one.There are more lines indirectly tied to alien life and the overall tone is always casual and nonchalant so I think it safe to assume that while not explained directly: - non-intelligent life is fairly common and of limited threat to humans (but enough to require military intervention here and there): - intelligent life is present and somewhat common with at least one specific example in the Arcturians; they are also physiologically close / compatible with humans via /r/movies https://ift.tt/3mxpRR2