On pages 175-176, Coyne describes what he calls divergent selection, based on geographic barriers in flowering plants, hummingbirds, and bees. He suggests that in one isolated region containing more hummingbirds than bees, flowers may evolve to become better suited to pollination by hummingbirds than bees- and the other way around in a region characterized by more bees. Then he speculates, that over time, should these two types of flowers that have evolved distinctly from one another suddenly be placed in the same location, the geographic barrier having disappeared, and the area containing equal amounts of bees and hummingbirds, then these flowers would each have their own type of pollinator and would not cross pollinate as a result, for they are now two different species. How difficult is it to maintain the ability to mix genes with closely related species (defining species by the definition given on page 172) or at least with those species derived from a common ancestor? Why would different species adapt their reproductive organs to become better suited for their own species rather than a wider range of potential mates? Wouldn't it be to the advantage of the flower placed back in the location described above to be able to be pollinated by both bees and hummingbirds? To what extent would it not? Why don't we see greater potential to mix genes and reproduce across species if sex has evolved as a means for genetic diversity?