Introduction

The chapters that follow in Part II deal with the diversity of cardiovascular development among the various phylogenetic groupings. The goal of this chapter, however, is to bring together some specific aspects of cardiovascular development beneath an evolutionary umbrella and to demonstrate that the study of cardiovascular change at an evolutionary level can provide insights into some of the basic concepts of cardiovascular development. Superficially, it may be difficult to see how this is possible. After all, evolutionary change is characterized as occurring either within or between populations over many generations and involving a change in gene distribution (Resnik, 1995). In contrast, developmental change occurs within an individual over one generation and need not involve a change in gene frequency. Hence, as recognized by Thompson (1917; see De Beer, 1958), ontogeny is concerned with the timing of the expression of certain genes, as well as with the relative rates of gene expression (expression of some genes may be accelerated, whereas for others it is retarded). Phylogeny is concerned more with whether or not specific genes are present and expressed. Yet it is clear that there are many similarities between certain aspects of cardiovascular change (sequences of events, changes in structures, and rearrangements of designs) occurring at an evolutionary level and those occurring during development. These similarities are explored in this chapter.

One false assumption that the reader may make about this chapter is that it resurrects the “theory of recapitulation.” It does not. Haeckel's theory of recapitulation stated that “ontogeny is a short recapitulation of phylogeny” and “phylogeny is the mechanical cause of ontogeny” (1866; as quoted by De Beer, 1958).