ABSTRACT
The work of D'Arcy Thompson, Alan Turing, Wolpert, and their successors provided a basis for the view that biological pattern and form are not specified by a detailed genetic program or blueprint, but are emergent properties of relatively simple processes occurring in particular physical or chemical contexts. What distinguishes biological patterns from chemical and physical ones is that the former have both an ontogenetic and an evolutionary history. Understanding biological pattern formation therefore requires explanation of the pattern, its ontogeny, and its diversity. Lewis Held has produced a formal taxonomy of pattern-forming models in development. The fact that theoretical models for biological pattern formation generally rely on diffusion or reaction-diffusion of molecules has been criticized by experimental developmental biologists on the grounds that the existence of diffusion morphogens has never been proven. The molecular-genetic mechanisms for patterning that have been elucidated to date appear to be relatively simple.
