Farmer and Norman Packard developed the concept of "metadynamics", i.e. co-evolving networks and dynamical systems. For example, the nodes of the network might represent chemical species and the edges their possible reactions, whose kinetics give rise to a system of differential equations. As new species are produced the set of reactions changes and the kinetics are in turn altered. This concept was used to model the immune system and the origin of life. Joint work with Richard Bagley produced a simulation of an autocatalytic set of polymers in which a few species are maintained at high concentration, with many of the properties of a metabolism; the autocatalytic set evolved through time in a manner resembling the evolution of living systems, but without a genetic code.