Evolution of the protein repertoire

Most proteins have been formed by gene duplication, recombination, and divergence. Proteins of known structure can be matched to about 50 % of genome sequences, and these data provide a quantitative description and can suggest hypotheses about the origins of these processes. During the course of evolution, forms of life with increasing complexity have arisen. What are the mechanisms that have produced the increases in protein repertoires that underlie the evolution of more complex forms of life? How are proteins organized to form path-ways? Answers to such questions at the mo-lecular level began to appear 40 years ago (1), but it is only with the advent of complete genome sequences that we have begun to get a comprehensive view