Why do men like women with flat stomachs and smooth skin? Because flat stomachs mean no pregnancy, and smooth skin indicates good health!
Why do women like strong men? Because it signifies their ability to better protect their offspring.
These aesthetic preferences evolved from ancient harsh environments and cannot be arbitrarily altered by interstellar civilizations. Indeed, a third-level civilization like humanity can alter appearances, but it can't change its fundamental aesthetic preferences.
If human civilization were altered to resemble frogs, human civilization would collapse in minutes. Aesthetics are a kind of philosophy contained within our genes!
Besides appearance being an important identifier for civilizations, other factors like survival environments, gravity, atmospheric pressure, air composition, and so on, are also critical identifiers.
The difficulty of altering such aspects is immense, and the probability of repetition among different civilizations is low.
