 A fourth discovery of evolutionary developmental biology was the importance of developmental plasticity for evolution (Nijhout 1990; Gilbert 2001; Pigliucci 2001). By the end of the 20th century, the roles of temperature, sunlight, diet, crowding, maternal behaviors, and predation were seen to have major roles in effecting phenotypes in plants and animals. Thus, the environment not only selected variations, it helped produce them. Since evo-devo postulated that changes in development cause evolution, and since developmental plasticity played a role in development, then it became necessary to look at changes in plasticity as being part of evolution. In the early years of the 21st century, developmental plasticity was seen to play roles in evolutionary change (West-Eberhard 2003; Abouheif et al. 2014; Suzuki &amp; Nijhout 2006; Rajakumar et al. 2018; Levis &amp; Pfennig 2020), and the notion of ‘plasticity-first evolution’ (or ‘development-first evolution’) integrated data from numerous sources into a program where the physiological ability to alter one’s phenotype due to environmental agents could become canalized and genetically fixed by selection. The mechanisms by which such plasticity-first evolution was effected (unmasking and selection of cryptic genetic variants, stress-related inability of molecular chaperones to allow proper folding of mutant proteins, etc.) became a new research program.