Making Sense of Transcription Networks

When transcription regulatory networks are compared among distantly related eukaryotes, a number of striking similarities are observed: a larger-than-expected number of genes, extensive overlapping connections, and an apparently high degree of functional redundancy. It is often assumed that the complexity of these networks represents optimized solutions, precisely sculpted by natural selection; their common features are often asserted to be adaptive. Here, we discuss support for an alternative hypothesis: the common structural features of transcription networks arise from evolutionary trajectories of “least resistance”—that is, the relative ease with which certain types of network structures are formed during their evolution. Have the structures of transcriptional networks evolved for optimal function under selective pressure or is neural drift through a course of “least resistance” a more likely explanation for their properties?