DEMYSTIFYING DARWIN'S MYSTERY OF MYSTERIES

Throughout the decades and into the present, we read of Darwin’s mystery of mysteries. This refers to the process by which new species come into being, or speciation, which some thought Darwin considered to be mysterious. In part, this characterization is discouraging, as we know a great deal about how new species form. The mystery over how species originate stems from the definition of species itself. Species concepts differ in their complexity and the types of biological aspects involved. The more complicated the species concept, the more mysterious speciation becomes. Even across different species concepts, there is little disagreement that speciation involves an allopatric phase. Nearly all avian sister species (by whatever definition) are allopatric or parapatric, and sympatry increases with genetic distance. The rank of species under the biological species concept requires reproductive isolation which can be pre-mating, post-mating, can involve ecological, behavioral, physiological and morphological characters, and involve many or few genes. If one adheres to the biological species concept, speciation is about as mysterious as it can be. This obtains because reproduction can occur in a large number of ways, perhaps never the same way twice. If one adopts a phylogenetic species concept, which requires only diagnosable taxa, speciation is not mysterious. In allopatry, divergence occurs via natural selection, sexual selection, or genetic drift, and from molecular data we have a range of estimates of how long this process occurs. I argue that at least in birds, the evolution of reproductive isolation is indeed mysterious, but because it need not be a part of how we define species, ignoring it demystifies speciation. Defining species based on diagnostic characters would result in greater exchange of information between paleontologists and neonatologists, except for the fact that I believe most speciation events in birds involve changes in vocal and plumage coloration, traits not evident in the fossil record.