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Abstract

The question of how a complex organism can develop from a Single fertilized egg has fascinated biologist for more than two centuries. In earlier times, basic insights have been obtained from experiments in which normal development has been perturbed. Like all other biological processes, development must be accomplished by interactions of molecules. From the regulations observed after experimental perturbations one cannot deduce directly the molecular interactions involved, however, these observations allow one to work out hypothetical interactions that have the same dynamic properties. A theory of development has to describe concentration changes of the relevant substances as functions of space and time. We have worked out several mathematically formulated models for different developmental situations that where able to describe many of the observations rather precisely. Since the molecular basis of development was completely unknown at that time, these models made firm predictions on the general types of interactions on which development is based.