The development of all units -- egg, embryo, regenerate, bud -- all involve the problem of emergent form.
-- N.J. Berrilll, Growth, Development and Pattern
One of the continuing enigmas in biology is how genes contribute to the process of embryonic development whereby a coherent, functional organism of specific type is produced. How are the developmental pathways stabilized and spatially organized to yield a sea urchin or a lily or a giraffe? The problem here is that genes are themselves participants in the developmental process. They do not occupy a privileged position in making decisions about alternative pathways of differentiation. Yet they clearly constrain the possibilities open to cells: lilies do not make muscle or nerve cells, giraffes do not make the water-conducting elements of plants. How do genes act and interact within the context of cells so as to bring about these units of structure and function? How do cells act and interact within the context of the organism to generate coherent wholes, the different types of organism that populate the planet? It is not genes that generate this coherence, for they can only function within the living cell, where their activities are highly sensitive to context. The answer has to lie in principles of dynamic organization that are still far from