Every living cell employs a network of chemical reactions to construct and control a huge variety of chemical compounds. Biologists, physicists, and mathematical scientists have developed and applied techniques of network analysis to study how biochemical compounds interact with one another. The studies suggest that very complex biological systems may result from the interconnection of far simpler processes, and further suggest that insight into complex systems may be gained from models that are themselves conglomerates or networks of simpler models.
Here I discuss four theoretical papers, each describing how a specific network carries out a function in a particular group of organisms. Painstaking work of biologists has filled in tens of thousands of reaction processes occurring in cells and has told us what reactions are important for a given biological function. Thus the biologists traced out the interactions among the different chemical compounds that work together. Those connections have given...