Marc Ereshefsky

The question of whether biologists should continue to use the Linnaean hierarchy has been a hotly debated issue. Invented before the introduction of evolutionary theory, Linnaeus's system of classifying organisms is based on outdated theoretical assumptions, and is thought to be unable to provide accurate biological classifications. Marc Ereshefsky argues that biologists should abandon the Linnaean system and adopt an alternative that is more in line with evolutionary theory. He traces the evolution of the Linnaean hierarchy from its introduction to the present. He illustrates how the continued use of this system hampers our ability to classify the organic world, and then goes on to make specific recommendations for a post-Linnaean method of classification. Accessible to a wide range of readers by providing introductory chapters to the philosophy of classification and the taxonomy of biology, the book will interest both scholars and students of biology and the philosophy of science.

A number of authors argue that while species are evolutionary units, individuals and real entities, higher taxa are not. I argue that drawing the divide between species and higher taxa along such lines has not been successful. Common conceptions of evolutionary units either include or exclude both types of taxa. Most species, like all higher taxa, are not individuals, but historical entities. Furthermore, higher taxa are neither more nor less real than species. None of this implies that there is no distinction between species and higher taxa; the point is that such a distinction is more subtle than many authors have claimed.

This paper examines the species problem in microbiology and its implications for the species problem more generally. Given the different meanings of ‘species’ in microbiology, the use of ‘species’ in biology is more multifarious and problematic than commonly recognized. So much so, that recent work in microbial systematics casts doubt on the existence of a prokaryote species category in nature. It also casts doubt on the existence of a general species category for all of life (one that includes both prokaryotes and eukaryotes). Prokaryote biology also undermines recent attempts to save the species category, such as the suggestion that species are metapopulation lineages and the idea that ‘species’ is a family resemblance concept.

A number of authors have argued that the thesis that species are individuals has important implications for macroevolutionary theory. More specifically, some authors claim that the thesis lends support to the Theory of Punctuated Equilibrium and indicates the existence of species selection. In this paper, I argue that the alleged individuality of species is neither necessary nor sufficient for the truth of that theory or for the existence of species selection. I also argue, contrary to the claims of some, that the individuality of a group is not a necessary requirement for a group to be a unit of selection.

Darwin offered an intriguing answer to the species problem. He doubted the existence of the species category as a real category in nature, but he did not doubt the existence of those taxa called ‘‘species’’. And despite his scepticism of the species category, Darwin continued using the word ‘‘species’’. Many have said that Darwin did not understand the nature of species. Yet his answer to the species problem is both theoretically sound and practical. On the theoretical side, DarwinÕs answer is confirmed by contemporary biology, and it offers a more satisfactory answer to the species problem than recent attempts to save the species category. On the practical side, DarwinÕs answer frees us from the search for the correct theoretical definition of ‘‘species’’. But at the same time it does not require that we banish the word ‘‘species’’ from biology as some recent sceptics of the species category advocate. Ó The Willi Hennig Society 2010

We tend to think that there are different types of biological taxa: some taxa are species, others are genera, while others are families. Linnaeus gave us his ranks in 1731. Biological theory has changed since Linnaeus’s time. Nevertheless, the vast majority of biologists still assign Linnaean ranks to taxa, even though that practice is at odds with evolutionary theory and even though it causes a number of practical problems. The Linnaean ranks should be abandoned and alternative methods for displaying the hierarchical relations of taxa should be adopted

Paul Thompson, John Beatty, and Elisabeth Lloyd argue that attempts to resolve certain conceptual issues within evolutionary biology have failed because of a general adherence to the received view of scientific theories. They maintain that such issues can be clarified and resolved when one adopts a semantic approach to theories. In this paper, I argue that such conceptual issues are just as problematic on a semantic approach. Such issues arise from the complexity involved in providing formal accounts of theoretical laws and scientific explanations. That complexity is due to empirical and pragmatic considerations, not one's adherence to a particular formal approach to theories. This analysis raises a broader question. How can any formal account properly represent the complex nature of empirical phenomena?