The world is biologically complex. Scientists have always known this and it is not a new discovery. Rather than accepting complexity as an everyday wonder, scientists are surprised that the world is indeed complex and some are annoyed with those who describe complexity in simple statements or methods. Here are a couple of examples:
"Historical biogeography has recently experienced a significant advancement in three integrated areas. The first is the adoption of an ontology of complexity, replacing the traditional ontology of simplicity, or a priori parsimony; simple and elegant models of the biosphere are not sufficient for explaining the geographical context of the origin of species and their post-speciation movements, producing evolutionary radiations and complex multi-species biotas" (Brooks, 2005: 79).We see no problem with simplifying a complex world in order to communicate in the form of classifications. We know for instance that a cat is a highly complex creature. So complex in fact, that the term cat or Felis silvestris and the classification of the Felidae are satisfactory in communicating that we are in fact referring to a tabby and everything associated with its complexity. These terms and classification are not however sufficient in explaining the highly complex nature of cat behaviour, sexual reproduction or neural activity. Classification is not about explaining complexity - this is job of General Biology.
"The problem can be reduced to deciding when a collection of trees—a 'forest'—is a better explanation for evolutionary relationships among a set of sequences than is a single tree" (Ane and Sanderson 2005: 146).
Classification, an integral part of comparative biology, attempts to convey what information we have (i.e., about cats) without having to divulge and detail all its complexity (i.e., sexual behaviour). The aim of classification is to summarize (not reduce*) a relationship based on known homologues without recourse to inference. That means, comparative biology is about "simplicity" not causality or interconnectivity (sensu reductionism). We can for instance classify all mammals based on their hair and vertebrates based on the presence of forearms. The more complexity we introduce, the less unique traits there are to compare (i.e., eye colour). Since comparative biology is about comparing and classifying, explicit unobserved explanatory mechanisms have little to do classifications. They are statements about a type of complexity reserved for general biology (i.e., physiology, behaviour, sexual reproduction etc.). Although such explanations are unique events (or a series of events) based on careful considerations of general biological laws and processes, they can however be represented by a single classification.
Let us say for instance that the trilobite Eoharpes guichenensis evolved from E. cristatus which then evolved into E. primus. This can be represented as an anagenetic event and drawn accordingly. Another person may object to this explanation and suggest that E. guichenensis evolved into E. cristatus and E. primus through cladogenesis. Another may see that both explanations have avoided the explanation that E. guichenensis evolved in E. primus and E. primus into E. cristatus.
Regardless of how these species of Eoharpes have evolved, the phylogenetic trees and be summarized or simplified as relationships in the cladogram: E. guichenensis (E. cristatus, E. primus). What is more, is that the nodes on the cladogram are not events, ancestors or morphotypes, but simply junctions supported by homologues. Rather than accepting the cladogram as means of communicating three or more different evolutionary scenarios, it is rejected as being too simplistic or as an explicit scenario (i.e. "cladification" of Mayr and Bock, 2002).
As systematists and biogeographers, that is comparative biologists, we study the shadows of the past. We are at best able to find gross relationships between taxa or areas. The ability to extract any pattern at all from the bits and pieces of information at hand is an extraordinary achievement, but for some this is not enough. A complex world it seems must be shown to be complex, as though this something that is not already appreciated. The ability to communicate and understand such complexity is impossible without "simplification", that is, classifications. Simplifying the complexity that surrounds us is not a crime but a way to understand the world and to communicate that information to others. Without classification, complexity becomes a curse, which leaves us dumbfounded in a sea of information.
*It is important to note that reduction is not simplification. Mechanical explanations for instance are reductions. The philosophy of reductionism revolves around causality and not natural classification.
Ané, C. & Sanderson, M.J. 2005. Missing the Forest for the Trees: Phylogenetic Compression and Its Implications for Inferring Complex Evolutionary Histories. Systematic Biology 54: 146 – 157.
Brooks D.R. 2005. Historical biogeography in the age of complexity: expansion and integration. Revista Mexicana de Biodiversidad vol. 76: 79- 94
Mayr, E. & Bock, W.J. 2002. Classifications and other ordering systems. Journal of Zoological Systematics and Evolutionary Research, 40, 169-194.