We visualise developmental biology as the study ofprogressive changes that occurwithin cells, tissues and organisms themselves during their life span. A good exampleofa field ofdevelopmentalbiology in whichthis conceptis encapsulatedis thatofsomitogenesis. The somitewas identifiedas the primordialunit underlyingthe segmentedorganisationofvertebrates more than two centuries ago. The spectacular discoveries and achievements inmolecularbiologyin the last fifty years have created a gene-basedrevolution in both the sorts ofquestions as well as the approaches one can use in developmental biology...