Using fixed number of base pairs rather than different number to encode all amino acids manifests that organisms probably do not know the distribution of amino acids across all protein sequences and assume equal probability for all amino acids. In this way organisms can change protein sequences and amino acid distributions flexibly and efficiently under changing environments. Otherwise, organisms have to change the codon system when the distributions change. For evolution, it is impossible for a living organism to know the future protein sequences and the amino acid distributions across the sequences. In order to generate any unknown future sequences efficiently, living organisms need to use a mechanism that can encode any protein sequences efficiently. In fact, all organisms use a mechanism that can reduce the maximal entropy to 0, which means equal probability for all amino acids when encoding protein sequences. For the same reason, organisms may not know the distribution of bases across all nucleotide sequences, and may assume equal probability for all bases even though the actual probability distribution across some genomes may not be equal at all. For biological information, most cases are like this with maximum entropy needed to be reduced and equal probability need to be assumed by organisms, so formula I=log(N) can be used to calculate the information.