"THE MOLECULAR BASIS OF COMPLEXITY: USING NETWORK ANALYSIS TO UNDERSTAND EVOLUTION" THE NOTION THAT BIOCHEMICAL PATHWAYS PORTEND EVOLUTIONARY HISTORY IS AS OLD AS THE STUDY OF THE PATHWAYS THEMSELVES. WHILE EARLY EFFORTS WERE TUNED TOWARDS PREBIOTIC CHEMISTRY - BEST PORTRAYED IN THE STATEMENT "METABOLISM RECAPITULATES BIOGENESIS," MORE RECENT STUDIES SUPPORT THE IDEA THAT WITHIN THE ARCHITECTURE AND TOPOLOGY OF BIOCHEMICAL NETWORKS IS EMBEDDED KEY INFORMATION ON THEIR EVOLUTION, RECRUITMENT OF GENES AND METABOLITES ACROSS THE NETWORK, ACQUISITION OF NEW FUNCTIONS FROM OTHER ORGANISMS, AND WHOLESALE DUPLICATIONS OF METABOLIC PATHWAYS. WHILE IN MANY WAYS ANALOGOUS TO THE HISTORICAL INFORMATION RECORDED IN GENE AND PROTEIN SEQUENCES, THE REQUIREMENTS FOR EXTRACTING EVOLUTIONARY INFORMATION ARE FUNDAMENTALLY DIFFERENT THAN THOSE USED FOR SEQUENCE ANALYSIS. THE GOAL OF THIS PROPOSAL IS TO DEVELOP A NEW APPROACH THAT INTEGRATES INFORMATION ON THE EVOLUTIONARY HISTORY OF ALL ENZYMES WITHIN A BIOCHEMICAL NETWORK WITH THE NEWLY DEVELOPED CAPABILITY TO MODEL NETWORK BEHAVIOR, NOT ONLY AS A FUNCTION OF THE AVAILABLE REPERTOIRE OF ENZYMES BUT ALSO CLOSELY APPROXIMATING THE CHANGING CHEMICAL MILIEUS THOUGHT TO HAVE EXISTED THROUGHOUT THE HISTORY OF THE EARTH.