Have you been making a list over the years like me? If so, you did what I didn't, and made notes, and you've brought up some I'd forgotten about.
Many alien races are derived from Earth creatures: insects, lizards etc.
Quite right! In fairness, vaguely insectoid life elsewhere doesn't seem extremely implausible. Where my suspension of disbelief suffers is when roughly human sized and shaped aliens are insectoid. The same goes for reptilians. This also connects with the observation that many sci-fi species have recognisably human gender characteristics. A five foot eight inch tall clearly female reptile woman, with boobs? Seems highly unlikely.
The predominance of Roman, Greek or ancient Egyptian fashions and architecture among intelligent humanoid alien races.
I hadn't actually really noticed this one. I'd add 'Nazi' style fascist societies as being overly represented among alien humanoids. There are probably others. I suppose it's a kind of narrative shorthand.
The concept of "desert planets" (or ice planets, etc.) where the temperature is bearable for humans, yet strangely uniform from pole to equator to other pole.
Nearly all planets have near Earth-normal gravity. (Written SF from the classic era is rather better in this regard, but films and series are rubbish at it.)
Oh, how could I have forgotten this particularly persistent bugbear from my earlier posts? The planet of a single geographical feature, still large enough to have Earthlike gravity, and able to support human life, even though it's entirely covered by ice, or rock, or desert.
Star Wars is a particular offender, of course, but I kind of give it a pass because it's two thirds fantasy anyway.
Slave traders in a universe where AI, robots and machinery can do pretty much anything a slave can do, but better.
Yeah, what's that all about? Machines are more reliable, require less rest, are less likely to rise up against their owners. Can be stored upright in a cupboard without constantly complaining.
Not only that, but the majority of alien species can breathe an Earth-normal atmosphere. It is always presented as a "scientific detail" if one species needs a special breathing medium.
Yes, so you get space stations full of species from all over the galaxy, most of which are not, for some reason, lying on the floor, dead or gasping for breath.
"My scanner is detecting life forms..." From orbit, you are somehow able to pick up evidence of life forms, not by their cities, roads, or visible presence, but by some strange bio-radiation that scanners can detect.
Also on the subject of, "My scanner is detecting lifeforms..." It is always assumed this means intelligent animals. No one ever says, "Oh, it might just be bacteria, or grass, or fish, or field mice."
Scanners have always perplexed me. I'm not sure on what kind of radiation most of them work, or whether they actively send out radiation or passively receive it from the targets, or both, since ships seem to know when they're being scanned. What information they give seems highly plot driven. Sometimes it's 'scanners are detecting life aboard, captain.' Other times it's, 'scanners are detecting four lifeforms, including one Farcican chewing some gum, a Unlikelian scratching his balls, A Ridiculon with five credits thirty two cents in his pocket, and a Stupidoid who usually smokes a pipe but is on nicotine patches.'
