The morphogenesis of evolutionary developmental biology

Evolution is not a speculation but a fact; and it takes place by epigenesis. Thomas Huxley (1893) p. 202 But it has become increasingly clear from research in embryology that the processes whereby the structures are formed are as important as the structures themselves from the point of view of evolutionary morphology and homology. Gavin de Beer (1954) p. 136 Developmental biology is experiencing a two-fold revolution. The first phase of the revolution began in the 1970s, when developmental biology began to make use of recombinant DNA technologies to explain the mechanisms by which genetic instruc-tions specified phenotypes composed of different cell types and organs. This newly empowered science identified the transcription factors, paracrine factors, and signal transduction cascades in-volved in the two most central processes of developmental biol-ogy—differentiation and induction. This ongoing phase of th