A sound understanding of the interrelationship between evolutionary theory and taxonomic theory is probably more important now than it ever has been since Darwin first developed his theory of evolution in The Origin of Species by Means of Natural Selection. This is not just because there are doubts over the precise nature of this relationship, as exemplified in the debate on pattern and process in taxonomy, but also because there are advances being made in other biological disciplines, such as molecular genetics, immunology, protein chemistry and microbiology, which call into question the limits of our understanding of structure and function in biological systems.

Since Darwin, the hierarchy, as discovered in nature through classification, has been wedded to evolutionary theory. Evolution provided an explanation which accounted for our perception of the hierarchy. In the past decade, this view has come under fire from a number of quarters, most conspicuously from taxonomists themselves. Surprisingly this attack has not been grounded in recent advances from other empirical disciplines: rather, taxonomists have argued over what the ‘proper’ methods of classification should be, generally motivated by a desire to find some adamantine system which is not at the mercy of theoretical change. The situation has some similarities with early twentieth-century physics, where in the face of a rapidly advancing theoretical science, retrenchment to a position of dogmatism by opponents of the advances was never very far away.