On the dynamics of evolutionary discontinuities

Intraspecific competition and selection in polymorphic populations are considered as gradual, yet highly nonlinear, processes which possibly lead to structurally unstable states in species and ecosystems. Discontinuous genetic and morphological changes may thus occur, which are interpreted as evolutionary “catastrophes,” that is, instantaneous transitions between distant, secularly stable evolutionary branches. It is argued that evolutionary gradualism and saltationism represent complementary modes of macroevolution corresponding respectively to the local and global topographical structure of adaptive surfaces.