Biological species have been treated traditionally as spatiotemporally unrestricted classes. If they are to perform the function which they do in the evolutionary process, they must be spatiotemporally localized individuals, historical entities. Reinterpreting biological species as historical entities solves several important anomalies in biology, in philosophy of biology, and within philosophy itself. It also has important implications for any attempt to present an "evolutionary" analysis of science and for sciences such as anthropology which are devoted to the study of single (...) species. (shrink)

Ernst Mayr has argued that Darwinian theory discredited essentialist modes of thought and replaced them with what he has called "population thinking". In this paper, I characterize essentialism as embodying a certain conception of how variation in nature is to be explained, and show how this conception was undermined by evolutionary theory. The Darwinian doctrine of evolutionary gradualism makes it impossible to say exactly where one species ends and another begins; such line-drawing problems are often taken to be the decisive (...) reason for thinking that essentialism is untenable. However, according to the view of essentialism I suggest, this familiar objection is not fatal to essentialism. It is rather the essentialist's use of what I call the natural state model for explaining variation which clashes with evolutionary theory. This model implemented the essentialist's requirement that properties of populations be defined in terms of properties of member organisms. Requiring such constituent definitions is reductionistic in spirit; additionally, evolutionary theory shows that such definitions are not available, and, moreover, that they are not needed to legitimize population-level concepts. Population thinking involves the thesis that population concepts may be legitimized by showing their connections with each other, even when they are not reducible to concepts applying at lower levels of organization. In the paper, I develop these points by describing Aristotle's ideas on the origins of biological variation; they are a classic formulation of the natural state model. I also describe how the development of statistical ideas in the 19th century involved an abandoning of the natural state model. (shrink)

The concept of individuality as applied to species, an important advance in the philosophy of evolutionary biology, is nevertheless in need of refinement. Four important subparts of this concept must be recognized: spatial boundaries, temporal boundaries, integration, and cohesion. Not all species necessarily meet all of these. Two very different types of pluralism have been advocated with respect to species, only one of which is satisfactory. An often unrecognized distinction between grouping and ranking components of any species concept is necessary. (...) A phylogenetic species concept is advocated that uses a grouping criterion of monophyly in a cladistic sense, and a ranking criterion based on those causal processes that are most important in producing and maintaining lineages in a particular case. Such causal processes can include actual interbreeding, selective constraints, and developmental canalization. The widespread use of the biological species concept is flawed for two reasons: because of a failure to distinguish grouping from ranking criteria and because of an unwarranted emphasis on the importance of interbreeding as a universal causal factor controlling evolutionary diversification. The potential to interbreed is not in itself a process; it is instead a result of a diversity of processes which result in shared selective environments and common developmental programs. These types of processes act in both sexual and asexual organisms, thus the phylogenetic species concept can reflect an underlying unity that the biological species concept can not. (shrink)

The “species-as-individuals” thesis takes species, or taxa, to be individuals. On grounds of spatiotemporal boundedness, any biological entity at any level of complexity subject to evolutionary processes is an individual. From evolutionary theory flows an ontology that does not countenance universal properties shared by evolving entities. If austere nominalism were applied to evolving entities, however, nature would be reduced to a mere flow of passing events, each one a blob in space–time and hence of passing interest only. Yet if there (...) is genuine biodiversity in nature, if nature is genuinely carved into species, and taxa, then these evolutionary entities will be genuinely differentiated into specific kinds, each species being one of its kind. Given the fact that evolving entities have un-sharp boundaries, an appropriately weak, “non-essentialist” concept of natural kind has to be invoked that does not allow for strong identity conditions. The thesis of this paper is that species are not either individuals, or natural kinds. Instead, species are complex wholes (particulars, individuals) that instantiate a specific natural kind. (shrink)

Biologists and philosophers have long recognized the importance of species, yet species concepts serve two masters, evolutionary theory on the one hand and taxonomy on the other. Much of present-day evolutionary and systematic biology has confounded these two roles primarily through use of the biological species concept. Theories require entities that are real, discrete, irreducible, and comparable. Within the neo-Darwinian synthesis, however, biological species have been treated as real or subjectively delimited entities, discrete or nondiscrete, and they are often capable (...) of being decomposed into other, smaller units. Because of this, biological species are generally not comparable across different groups of organisms, which implies that the ontological structure of evolutionary theory requires modification. Some biologists, including proponents of the biological species concept, have argued that no species concept is universally applicable across all organisms. Such a view means, however, that the history of life cannot be embraced by a common theory of ancestry and descent if that theory uses species as its entities.These ontological and biological difficulties can be alleviated if species are defined in terms of evolutionary units. The latter are irreducible clusters of reproductively cohesive organisms that are diagnosably distinct from other such clusters. Unlike biological species, which can include two or more evolutionary units, these phylogenetic species are discrete entities in space and time and capable of being compared from one group to the next. (shrink)

Although it is possible to regard a species as a set with a special internal structure, it is preferable to regard a species as an individual precisely to emphasize this internal structure. It is necessary to recognize, moreover, that two organisms that are part of a single entity with respect to one process need not be part of a single entity with respect to another process. Furthermore, choosing to regard two entities (with respect to one process) as conspecific is not (...) to deny that there are two entities within this species. Thus, the systematist need not propose formal names for every entity he discovers, but the names he proposes ought to be as faithful to the relationship among the entities as is possible. (shrink)

It has been argued that human restoration of nature is morally problematic because artificially restored natural entities are artifacts, which are ontologically different from natural entities and hence essentially devoid of the moral standing that natural entities have. I discuss the alleged assimilation of restored natural entities to artifacts, and argue that it does not follow from the ontological differences, if any, between the artifactual and the natural that the former is morally inferior to the latter. This defense against the (...) devaluation of restored natural entities is aimed at narrowing the ethical gap between the wild and thetamed, which is often endorsed by ecocentric environmental ethics. (shrink)

Scientists must sometimes choose between competing definitions of key terms. The degree to which different definitions facilitate important dis- coveries should ultimately guide decisions about which terms to accept. In the short run, rules of thumb can help. One such rule is to regard with suspicion any definition that turns a seemingly important empiri- cal matter into an a priori exercise. Several prominent definitions of eco- logical “stability” are suspect, according to this rule. After evaluating alternatives, I suggest that the (...) faulty definitions resulted from an over- emphasis on population dynamics in community ecology. Machine met- aphors of nature may have given rise to a related problem of experimen- tal design. (shrink)

Scientists must sometimes choose between competing definitions of key terms. The degree to which different definitions facilitate important discoveries should ultimately guide decisions about which terms to accept. In the short run, rules of thumb can help. One such rule is to regard with suspicion any definition that turns a seemingly important empirical matter into an a priori exercise. Several prominent definitions of ecological “stability” are suspect, according to this rule. After evaluating alternatives, I suggest that the faulty definitions resulted (...) from an overemphasis on population dynamics in community ecology. Machine metaphors of nature may have given rise to a related problem of experimental design. (shrink)

A major issue in philosophical debates on the species problem concerns the opposition between two seemingly incompatible views of the metaphysics of species: the view that species are individuals and the view that species are natural kinds. In two recent papers in this journal, Olivier Rieppel suggested that this opposition is much less deep than it seems at first sight. Rieppel used a recently developed philosophical account of natural kindhood, namely Richard Boyd’s “homeostatic property cluster” theory, to argue that every (...) species taxon can be conceived of as an individual that constitutes the single member of its own specific natural kind. In this paper I criticize Rieppel’s approach and argue that it does not deliver what it is supposed to, namely an account of species as kinds about which generalized statements can be made. (shrink)

We attempt to defend the species-as-individuals hypothesis by examining the logical role played by the binomials (e.g., "Homo sapiens," "Pinus ponderosa") in biological discourse about species. Those who contend that the binomials can be properly understood as functioning in biological theory as singular terms opt for an objectual account of species and view species as individuals. Those who contend that the binomials can in principle be eliminated from biological theory in favor of predicate expressions opt for a predicative account of (...) species and view species as kinds. We contend that biologists' talk about species is talk about species as individuals, and we conclude that the most plausible account of species is an objectual account. (shrink)

We examine the evolution of the concept of stability in community ecology, arguing that biologists have moved from an emphasis on biotic communities characterized by static balance, to one of dynamic balance (returning to equilibrium after perturbation), to the current concept of stability as persistence. Using Wimsatt's (1987) analysis of how false models can often lead to better ones, we argue that failed attempts to link complexity with stability have significant heuristic value for community ecologists. Nevertheless, we argue that, (A) (...) because there is no common characteristic that stability terms presuppose, community ecology might be better served by abandoning the concept of stability and by employing instead specific terms such as 'persistence', 'resistance', and 'variability'. (B) The current emphasis (of stability terms) on persistence of species provides little basis for explaining possible mechanisms that might account for persistence. (shrink)