We discuss theoretical and experimental approaches to three distinct
developmental systems that illustrate how theory can influence experimental work
and vice-versa. The chosen systems – Drosophila melanogaster,
bacterial pattern formation, and pigmentation patterns – illustrate the
fundamental physical processes of signaling, growth and cell division, and cell
movement involved in pattern formation and development. These systems exemplify
the current state of theoretical and experimental understanding of how these
processes produce the observed patterns, and illustrate how theoretical and
experimental approaches can interact to lead to a better understanding of
development. As John Bonner said long ago
`We have arrived at the stage where models are useful to suggest
experiments, and the facts of the experiments in turn lead to new and improved
models that suggest new experiments. By this rocking back and forth between the
reality of experimental facts and the dream world of hypotheses, we can move
slowly toward a satisfactory solution of the major problems of developmental
biology.'