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Positive Darwinian Selection in Gene Evolution

When Charles Darwin proposed the theory of evolution by natural selection, he was concerned with phenotypic evolution. Because all phenotypes have their genetic basis, natural selection indirectly acts on genotypes through its action on phenotypes. In this article, I review the roles of positive Darwinian selection in the evolution of genes, focusing on the work conducted in my laboratory in the last decade. Using real examples, I show that different forms of positive selection can promote amino acid substitutions, cause parallel amino acid changes, increase the rate of insertion/deletion substitutions, accelerate gene loss, and enhance gene expression noise. Although positive selection probably does not account for the majority of changes in DNA sequence evolution, it can and did shape DNA sequence evolution in many different ways and is undoubtedly an important force in molecular evolution.