How Do Functional New Complex Networks Evolve?
Complex traits require co-ordinated expression of many transcription factors and signaling pathways to guide their development. Creating a developmental program de novo would involve linking many genes one-by-one, requiring each mutation to drift into fixation, or to confer some selective advantage at every intermediate step in order to spread in the population. While this lengthy process is not completely unlikely, it could be circumvented with fewer steps by recruiting a top regulator of an already existing gene network, i.e., by means of gene network co-option. Subsequent modifications of the co-opted network could further optimize its role in the new developmental context. Gene network co-option is hardly a new concept, but surprisingly, no test has ever been developed to distinguish it from alternative mechanisms. While gene network co-option is often proposed to explain instances where the same set of developmental genes are expressed in two different developmental contexts [8–14
