There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact. Mark Twain The recent explosion in ou. r knowledge of basis physiologic processes, molecular biology, and genetic regulatory mech anisms has resulted, in large measure, from a single concep tual advance: the realization that, at the molecular level, evolutionarily divergent organisms are more similar than different. Thus, in Escherichia coli and Homo sapiens, the enzymatic pathways for the utilization of galactose and glu cose are the same, although more than...