Why do ppl have a preference for certain features in humans?

i hate ot gneralise but just bear with me..why do so many ppl (not all but majority) preffer blue or green eyes? What makes ppl have a preference for smaller noses as opposed to large noses? is there a scientific explanationn for it all?..like example: ppl like ppl with clear skin cause it shows the person is in good health therefore clear skin is more attractive..just an example..how about long hair on girls as opposed to short hair..can you give me resons why a feature is more popular or is considered more beautifull and the reasons behind it? thanks…i know beauty is in the eye of the beholder but let's face it there are certain facial feature preferences with models etc that tend to be more popular