system
Given the following post, respond as if you're commenting on Reddit:
human
Of the 64 potential amino acids, why does the human body only utilize 20 of them? 

Additionally, could "foreign" amino acids code for gene expression, or even physical manifestations of things we have never seen - or would our DNA repair techniques oust new amino acids that are introduced to our genome?
gpt
It's backwards.  Codons evolved to represent the 20+ amino acids.  Although there are 64 codons, many are duplicates, coding for the same amino acid.  There's no such thing as "foreign" amino acids becoming integrated into our cells as it's impossible to code them by the existing coding scheme.  Even if you somehow brought alien amino acids to earth, they would go unused as protein build blocks.