When the human human brain is discussed, I frequently hear an argument that goes like this "If there was a simple chemical solution for people to be smarter, nature would've already found it". I'm thinking about the probability of discovering (either naturally or pharmacologically) an agent that would make humans smarter.
Assuming that a cell is a biological computer which "computes in terms of proteins", there are 5000(?) different proteins per cell, there are X billion of humans/ancestors that have been around, a gene for each protein could've mutated at some point in the past. As far as I understand, proteins are made of amino acids through some metabolic cycle. Does this mean that there's a finite number of proteins that are possible within a human brain cell? Does science have a rough idea of what percentage of different kinds of proteins have been "found" and tried by brain cells over the history of humans/primates? Is it 1%? 25%?