I wonder why life uses the particular proteins that it does, about 10^6 different proteins, I think? Evolution cannot explain it because the number of possible proteins is far far too large to ever come into existence anywhere in the visible universe, let alone on Earth. And evolutionary selection only works on stuff that exists.
Is there some chemical or other explanation, or is this an unresolved paradox in biology?
The median number of amino acids in a human protein is 375. Most are longer than 200 and maybe all are longer than 100. The 20 different kinds of amino acids can be combined to 20^375 = 10^487 different proteins which have the length 375.
If the entire crust of the Earth consisted of proteins which all were 375 long and each protein mutated once every nanosecond during 5 billion years and each mutation resulted in a protein which is unique in time and space, and there exists 100 such "protein Earths" around every star and 1000 billion stars in each of 1000 billion galaxies in the visible universe, it still only adds up to something like 10^100 proteins. Adding 10^37 years until the last star remnant has cooled down to less than 1 Kelvin, doesn't change this picture, almost all of the possible proteins will literally never exist anywhere. Even if I'm off by a factor a million on each of those numbers, only one in 10^300 of all possible median length proteins could ever exist.
Since our mind-bendingly small subset of possible proteins supports life, shouldn't we expect that many many (as in 10^300) other potential subsets of different proteins would do so too? And can we conclude that if DNA/protein based life has originated somewhere else, it will not have even one single protein in common with us or with any other independent origin of life? Or is this focus on proteins somehow invalid?