Biological Networks: Does Function Follow Form?

Recently, studies of biological networks have focused on various topological measures (primarily degree distributions and subgraphs). Relating such graph-theoretic statistics to function is difficult, since a given topology does not uniquely determine function. In fact, a topology's ability to support multiple functions may itself provide a selective advantage to an organism, since a topology with multiple functions can be adaptable (on the time scale of the individual) or evolvable (on the time scale of the species). Here we present a quantitative measure of circuit function and use this measure to test if circuits with well-defined function or functions are common, and if evolvable topologies exist among them.