Divergent Uses of "Parallel Evolution" during the History of The American Naturalist

The mechanistic link between natural selection and parallel evolution is well established. Natural selection is the only known deterministic process that can regularly overcome chance and historical contingency to generate the evolution of similar characteristics in independent populations inhabiting similar environments. However, the ready inference of natural selection from parallel evolution has been established only relatively recently. Here, I review the use of "parallel evolution" in the first 125 years of The American Naturalist and show that there were other well-accepted definitions of the term through the history of the field. I discuss the legacy of those alternative ideas and how they helped to shape evolution and ecology as we know them today and finish by discussing a geometric use for "parallel" that may reduce terminological confusion.