Evolving responsively: Adaptive mutation

A basic principle of genetics is that the likelihood that a particular muta tion occurs is independent of its phenotypic consequences. The concept of a daptive mutation seemed to challenge this principle with the discoveries of mutations stimulated by stress, some of which allow adaptation to the stre ss. The emerging mechanisms of adaptive genetic change cast evolution, deve lopment and heredity into a new perspective, indicating new models for the genetic changes that fuel these processes.