Speciation: Where Are We Now? An Introduction to a Special Issue on Speciation

Although modern evolutionary biology started with a seminal volume whose title identified the origin of species as the central theme of the new theory (Darwin 1859), the topic of speciation received relatively little attention for several decades following the publication of the origin of species. Darwin and his contemporaries devoted much more attention to explain how changes occurred within species rather than how species originated. In fact, a search of the published scientific literature using web of science reveals that between 1864 and 1939 only 21 journal articles had the word speciation in their title (Fig. 1). As already summarized by Coyne and Orr (2004) interest in the origin of species greatly increased during the development of the modern synthesis, when mendelian genetics was reconciled with biogeography and natural selection by people like Dobzhansky (1937) and Mayr (1942). Mayr was the first to focus on the importance of species, introducing the biological species concept (BSC), which has dominated speciation research for the past seven decades, and championed the idea of speciation in allopatry. Dobzhansky’s work pointed out the importance of understanding how changes in allele frequencies could produce genetically distinct groups and the importance of reproductive isolating mechanisms. Between the 1940s and the 1970s, while the biogeography of speciation remained an active area of research for systematists and naturalists, the mechanisms of origin of barriers to reproductive isolation received relatively little attention by geneticists. During that time period most workers in fact remained more interested in demonstrating the strength and influence of natural selection in the wild, and in explaining how genetic variation accumulates and persists within species (e.g., Lewontin 1974). Starting in the 1980s however, the availability of new empirical tools such as molecular genetics, and theoretical and methodological approaches, such as phylogenetic and comparative methods, led to resurgence in interest in the origin of species. Speciation research, once predominantly the domain of systematists, paleontologists, and some geneticists, started to attract the interests of workers in other fields of biology, such as ecologists, ethologists, genome biologists, and developmental biologists. This caused a shift from largely pattern-oriented studies of speciation, in which often the description of patterns was accompanied by the suggestion of some (often untestable) hypotheses regarding what might have caused the events, to more process-oriented studies, in which attempts were made to directly test and explore the process. This resurgence of interest in speciation has been one of the main developments in evolutionary biology during the past 25 years, and has led to a new phase of speciation studies (Coyne and Orr 2004). During this new phase many of the major conclusions about speciation reached since 1859 have been re-examined. The debate over species concepts, once mostly the domain of systematists and philosophers, was reinvigorated through the active involvement of students of different branches of biology (e.g., F. Santini (&) Department of Ecology and Evolutionary Biology, University of California at Los Angeles, 610 Charles Young Dr. South, Los Angeles, CA 90095, USA e-mail: santini@ucla.edu