The article reviews the concepts of phenotypic plasticity, genetic assimilation, and phenotypic accommodation, and their roles in evolutionary theory. It discusses the ongoing debate about these concepts, particularly the criticisms raised by G. de Jong regarding the importance of phenotypic plasticity and the lack of clear examples of genetic assimilation. The authors argue that phenotypic plasticity is a crucial mechanism for survival under novel environmental conditions, and that genetic assimilation can occur through selection on the expression of phenotypic plasticity. They also address the role of quantitative genetics in evolutionary theory, emphasizing that plasticity is a proximate cause of developmental changes, while natural selection is an ultimate cause of adaptation. The article concludes that these new perspectives on phenotypic plasticity and genetic assimilation are not a threat to the Modern Synthesis but rather an expansion of its current understanding, and that they are generally compatible with current quantitative genetic models.The article reviews the concepts of phenotypic plasticity, genetic assimilation, and phenotypic accommodation, and their roles in evolutionary theory. It discusses the ongoing debate about these concepts, particularly the criticisms raised by G. de Jong regarding the importance of phenotypic plasticity and the lack of clear examples of genetic assimilation. The authors argue that phenotypic plasticity is a crucial mechanism for survival under novel environmental conditions, and that genetic assimilation can occur through selection on the expression of phenotypic plasticity. They also address the role of quantitative genetics in evolutionary theory, emphasizing that plasticity is a proximate cause of developmental changes, while natural selection is an ultimate cause of adaptation. The article concludes that these new perspectives on phenotypic plasticity and genetic assimilation are not a threat to the Modern Synthesis but rather an expansion of its current understanding, and that they are generally compatible with current quantitative genetic models.