Natural Selection and the Concept of a Protein Space

SALISBURY¹ has argued that there is an apparent contradiction between two fundamental concepts of biology-the belief that the gene is a unique sequence of nucleotides whose function it is to determine the sequence of amino-acids in a protein, and the theory of evolution by natural selection. In brief, he calculated that the number of possible amino-acid sequences is greater by many orders of magnitude than the number of proteins which could have existed on Earth since the origin of life, and hence that functionally effective proteins have a vanishingly small chance of arising by mutation. Natural selection is therefore ineffective because it lacks the essential raw material-favourable mutations.