Progress on the Origin of Species

D espite the biases that a single author inevitably brings to a subject, only one or a few closely interacting authors can bring coherence, synthesis, and vision to a broad and complex topic. A symposium volume just doesn't do the job. Few topics in biology are as simultaneously encompassing, complex, and controversial as the origin of species, i.e., speciation. Speciation is, after all, the process responsible for biological diversity, at least of sexual organisms, so it is hardly a minor topic. But even though recent years have seen the publication of symposia on speciation and books on the ever-contentious issue of species concepts, it has been 23 years since Verne Grant's authoritative Plant Speciation [1] and 41 years since Ernst Mayr's magisterial and highly infl uential Animal Species and Evolution [2]—the last syntheses of research on speciation. Now, two outstanding new books not only treat speciation as a conceptually unifi ed topic in both plants and animals for the fi rst time, but also provide rich review and analysis of a vast subject that has progressed at least as much since Mayr and Grant wrote as in the century that preceded their work. These books are very different, but wonderfully complementary. Gavrilets reviews and adds to mathematical theories and simulation studies of speciation and related issues, such as fi tness landscapes and selection in heterogeneous environments. A deep reading of his book will require considerably more mathematical competence than most evolutionary biologists (including this reviewer) have, but Gavrilets provides excellent verbal explanations of the models' assumptions and conclusions, as well as comparisons and critiques of related models. Gavrilets cites empirical studies (with which he has very broad familiarity) plentifully, but as a theoretician, he does not evaluate them or describe them in depth. That task is undertaken by Coyne and Orr, who introduce most topics with a verbal overview of theory, review empirical evidence and its bearing on hypotheses, and conclude with incisive assessments of what they think we know and what remains uncertain or unexplored. Like Gavrilets, they offer a number of novel ideas or suggestions about how to proceed. Coyne and Orr have both worked mostly on speciation genetics in Drosophila, so it is hardly surprising that their treatment of speciation bears a strong genetic emphasis and draws heavily on Drosophila work (perforce, since this is almost the only source of evidence on some topics, such as the …