Metaphors and the role of genes in development.

In describing the flawless regularity of developmental processes and the correlation between changes at certain genetic loci and changes in morphology, biologists frequently employ two metaphors: that genes 'control' development, and that genomes embody 'programs' for development. Although these metaphors have an admirable sharpness and punch, they lead, when taken literally, to highly distorted pictures of developmental processes. A more balanced, and useful, view of the role of genes in development is that they act as suppliers of the material needs of development and, in some instances, as context-dependent catalysts of cellular changes, rather than as 'controllers' of developmental progress and direction. The consequences of adopting this alternative view of development are discussed.