I have been reading Sean Carroll’s book “Endless forms, Most beautiful”, which tracks recent progress in the field of evolutionary developmental biology. One of the themes of the book is the pivotal role of 'genetic switches’ within the genome, which determine when and where in the course of development of the embryo genes will be expressed. The activation of these switches is itself determined by proteins which themselves had been translated as a result of the action of other switches and so forth. Carrol writes: