6 - Intuiting Evolution

Summary

In this chapter I survey how biologists and paleontologists have used their imagination and evolutionary intuitions to animate phylogenetic narratives. Many authors intuited the direction of character evolution from clues provided by the threefold parallelism. The form changes that can be observed during ontogeny, and those inferred from the stratigraphic sequence of fossils, have inbuilt time axes that can be used as shortcuts for proposing lineages of changing forms. But interpreting the polarity of character change suggested by the systematic leg of the threefold parallelism was less straightforward. Many researchers intuited or imposed the direction of evolutionary change by proposing smoothly transitional linear series of observed or imagined forms. Some evolutionary intuitions date back to pre-evolutionary times, while others emerged from the search for evolutionary laws, such as Cope’s rule of phyletic size increase. When the first molecular phylogenies were published, researchers often muted their once vocal evolutionary intuitions to accept sometimes deeply puzzling results. The complete suppression of the evolutionary imagination is associated with the flawed but widespread strategy of using observed differences between taxa as prima facie evidence against monophyly and homology. It frequently diverts phylogenetic debates into fruitless avenues.