Genetic networks as transmitting and amplifying devices for natural genetic tinkering

Genes never act in isolation but only through webs of functional connections called 'genetic networks'. The term 'genetic network', however, embraces a number of conceptually distinct entities. These include metabolic gene networks, protein 'interactomes', transcriptional networks, and the molecularly diverse networks that underlie development. That last category is the most complex and the one of most direct relevance to morphological evolution. It will be argued here that most microevolutionary 'tinkering' involves changes in such genetic networks. Unfortunately, the conceptual and technical problems in elucidating and characterizing these networks are substantial. In consequence, relatively few developmental genetic networks, and their evolutionary alterations, have yet been characterized in any detail. Nevertheless, the generic functional properties of these networks can help explain certain aspects of evolutionary change. In particular, the ways that development genetic networks act as both transmitting and amplification devices for genetic change will be described. The relationship of these properties to the sometimes puzzlingly rapid rates of organismal evolution will be discussed.