The Controversial Cope’s, Haeckel’s and Dollo’s Evolutionary Rules: The Role of Evolutionary Retrogradation

The goal of this chapter is to discuss old problems and recent polemics related to the famous Cope’s, Dollo’s and Haeckel’s rules. The first concerns phyletic size increase: that sort of trend is observed in a multitude of phyla and shows several exceptions during periods of environmental stress. The second rule is discussed with some details because evolutionary reversions of trends are also frequent during stress episodes. The third trend, terminal addition, is very common and one can observe numerous cases where characters that are added late in phylogeny are also the first to be deleted during external stress phases. The addition of new elements at the end of ontogeny is frequently concomitant with size increases (Cope’s trend).