Perspective: Genetic assimilation and a possible evolutionary paradox: can macroevolution sometimes be so fast as to pass us by?

The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the "hardening" of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology.