In the chapter The Origin of Species, Coyne describes how the majority of species that form the diversity of the biosphere we live in. The predominant pro-evolution theory is that different species were caused by a single population being separated geographically and evolving in a different manner from its distanced kin until a point where if the two populations were reintroduced, they would be unable to reproduce with each other and therefore recombine their genes. However, can we really expect that of the millions (and perhaps billions depending on the classification system) of species in the world that they all were separated by a landmass forming across the sea or a mountain chain rising amidst a forest? Granted that the earth has been around for a long time and that the planet has changed a lot since life first inhabited it but what other possible ways could a population evolve separately from another population of the same species to the point where it can no longer share genes and becomes a different species? Dr. Coyne also gives the example of flowers adapting to different pollinators and therefore not being able to recombine their genes so obviously this one is exempt.