Erwin, D. H.
Arguments over macroevolution versus microevolution have waxed and waned through most of the twentieth century. Initially, paleontologists and other evolutionary biologists advanced a variety of non-Darwinian evolutionary processes as explanations for patterns found in the fossil record, emphasizing macroevolution as a source of morphologic novelty. Later, paleontologists, from Simpson to Gould, Stanley, and others, accepted the primacy of natural selection but argued that rapid speciation produced a discontinuity between micro- and macroevolution. This second phase emphasizes the sorting of innovations between species. Other discontinuities appear in the persistence of trends (differential success of species within clades), including species sorting, in the differential success between clades and in the origination and establishment of evolutionary novelties. These discontinuities impose a hierarchical structure to evolution and discredit any smooth extrapolation from allelic substitution to large- scale evolutionary patterns. Recent developments in comparative developmental biology suggest a need to reconsider the possibility that some macroevolutionary discontinuites may be associated with the origination of evolutionary innovation. The attractiveness of macroevolution reflects the exhaustive documentation of large-scale patterns which reveal a richness to evolution unexplained by microevolution. If the goal of evolutionary biology is to understand the history of life, rather than simply document experimental analysis of evolution, studies from paleontology, phylogenetics, developmental biology, and other fields demand the deeper view provided by macroevolution.