UNDERSTANDING THE ORIGIN OF SPECIES

Abstract

‘‘The origin of new species, signifying the origin of essentially irreversible discontinuities with entirely new potentialities, is the most important single event in evolution.’’ (Mayr 1963, p. 11). In proportion to its importance, speciation is poorly understood. Meaningful facts about speciation do not come easily, so progress is made at nearly the same slow but steady pace as the process itself. Dobzhansky’s Genetics and the Origin of Species, published in 1937, and Mayr’s Animal Species and Evolution, published in 1963, remain the only major books on speciation, and the 1989 volume Speciation and Its Consequences edited by Otte and Endler was the last compilation devoted to the subject. The recent effort edited by D. J. Howard and S. H. Berlocher is a collection of 33 chapters dedicated to Guy Bush, who broke ranks while a Harvard graduate student to study sympatric speciation. We are fortunate that the celebration of his 65th birthday provided an opportunity for a major review of speciation studies. Chapters are devoted to species concepts, modes of speciation, reproductive barriers, the genetics of speciation, and hybridization. As expected, sympatric speciation gets considerable attention, and all the contributors on this subject take a decidedly favorable stance. There is a dearth of papers on plants, but the new generation of botanists is to blame, not the organizers. Molecular phylogenies have replaced the extensive biosystematic studies that were once common in botany, and plant speciation studies have suffered as a result. Drosophila retain their status as the system of choice for studying the genetics of speciation. Ecology, as usual, gets short shrift. In the summary that follows I discuss some of the major topics and make suggestions for future work.