As dsRNA-mediated interference (RNAi) libraries become more widely available, genome-wide loss of function experiments in cell culture are likely to become a routine laboratory tool. RNAi screens can then be conducted to test gene functions in different assays in a variety of cell types and across species. In comparing these large phenotypic data sets, researchers will gain a new perspective, enabling them to see each gene as part of a fluid network that is remodelled in response to changes in environmental and developmental context, and with the passage of evolutionary time.