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.

In this chapter I discuss the anatomy of evolutionary storytelling. Historical narratives are woven around central subjects that lend them continuity through time. The central subjects of phylogenetic scenarios are lineages of hypothetical ancestors. These define the pathways of homology along which evolutionary change is reconstructed, and they root the power of phylogenetic hypotheses to explain the evolution of form by allowing characters in descendants to be traced back to ancestral precursors. De novo origins of novel traits are chinks in the explanatory armory of phylogenetic hypotheses. Hypothetical ancestors have therefore often been deliberately equipped with characters that provide suitable precursors of the traits that await evolutionary explanation. I will argue that the precursor potential of hypothetical ancestors functioned as an early phylogenetic optimality criterion used in the construction and judging of scenarios.

Finally, in this chapter I offer a concluding meditation on the undiminished value, indeed the necessity, of evolutionary storytelling, if our goal is to go beyond the trees and try to understand what may have happened along life’s myriad evolving lineages. As soon as one looks at a tree and asks ‘what does this mean?’, one becomes an evolutionary storyteller. Some dismiss such stories as pure fiction, and would prefer not to go beyond the tree. But for those of us who wish to peer over the phylogenetic frontier, these stories are how we generate our understanding of evolution, or at least how we try to.

This chapter explains why I wrote this book and it provides an outline of each chapter. This book traces the history of the scientific discipline that I call narrative phylogenetics from its origin in the second half of the nineteenth century to today. Narrative phylogenetics is a storytelling discipline that is concerned with tracing the evolution of lineages, and it is driven by speculations about the evolutionary process and the evolutionary descent of characters from precursors in hypothetical ancestors. Although phylogenetics has developed enormously since then, narrative phylogenetic reasoning remains visible in the scientific debates of today.