Embryonic Induction

Definition

Before the rise of genetics, Hans Spemann in 1901 already emphasized the role of inducers at the tissular scale, a role which can be played by many chemical substances, as Joseph Needham recognized later (Order and life), leading to the “paradox of an apparently nonspecific stimulus eliciting a specific developmental response” (Jacobson and Sater 1988, p. 341). Inducers trigger the development of sets of cells, morphogenetic fields, likely to develop into specific cell fates. The neural crest, for example, is a transitory structure which among other things gives rise to the nervous system. Morphogenetic fields can until some stage be induced into other fates by proper induction as it has been shown by Spemann and Mangold’s sea urchin experiments. This proves the plasticity proper to early development.

The experimental investigation of the nature of inducers as well as the relation between morphogenetic fields and organizers has been a main endeavor of embryology in the...