 When Davis retired from Harvard in 1911, the study of landscape evolution was nearly monopolized by his theories.It was characteristic of Davis to react violently and disdainfully to criticism, particularly to the German criticism in the 1920s headed by Walther Penck; it was also his characteristic to choose to attack the most vulnerable points of that criticism.Since that time, with a less dogmatic approach and greater knowledge, some authors note that Penck's and Davis' ideas have become more compatible and even complementary since the advent of modern tectonic theory.