Abstract

Since the early days of embryology, a central puzzle for biologists has been how a fertilized egg can execute a clearly defined and reproducible program that leads ultimately to a complex organism. It was clear that all of the information necessary to create the adult must already reside in the zygote, but how that information was translated into a complex organism was obscure. Even as recently as the late 1940s, the molecular mechanisms associated with early development were unknown and, in a sense, unknowable, given the available knowledge and technology. In the preceding centuries, embryologists had described in detail the progression of events during embryonic development, in both vertebrates and ..