This paper aims to offer a new argument in defence bacterial species pluralism. To do so, I shall first present the particular issues derived from the conflict between the non-theoretical understanding of species as units of classification and the theoretical comprehension of them as units of evolution. Secondly, I shall justify the necessity of the concept of species for the bacterial world, and show how medicine and endosymbiotic evolutionary theory make use of different concepts of bacterial species due to their (...) distinctive purposes. Finally, I shall show how my argument provides a new source of defence for bacterial pluralism. (shrink)

At least 22 concepts of species are in use today and many of these are notably incompatible in their accounts of biological diversity. Much of the traditional turmoil embodied in the species problem ultimately derives from the packaging of inappropriate criteria for species into a single concept. This results from a traditional conflation of function of concepts with their applications, definitions with concepts, taxonomic categories with groups, and the ontological status of real species with teleological approaches to recover them. Analogous (...) to classifications of supraspecific taxa, our forging inappropriate and ambiguous information relating to theoretical and operational discussions of species ultimately results in a trade-off between convenience, accuracy, precision, and the successful recovery of natural biological diversity. Hence, none of these expectations or intentions of species or classifications is attainable through composite, and possibly discordant, concepts of biological diversity or its descent. Reviewing and evaluating the concepts of species for their theoretical and operational qualities illustrates that a monistic, primary concept of species, applicable to the various entities believed to be species, is essential. This evaluation reveals only one theoretical concept as appropriate for species, the Evolutionary Species Concept. This conceptualization functions as a primary concept and is essential in structuring our ideas and perceptions of real species in the natural world. The remaining concepts are secondary, forming a hierarchy of definitional guidelines subordinate to the primary concept, and are essential to the study of species in practice. Secondary concepts should be used as operational tools, where appropriate, across the variance in natural diversity to discover entities in accord with the primary concept. Without this theoretical and empirical structuring of concepts of species our mission to achieve reconciliation and understanding of pattern and process of the natural world will fail. (shrink)

I should like to offer my greatest thanks to Paul Griffiths for providing the opportunity for this exchange, and to commentators Gillian Brown, Steven Fuller, Stefan Linquist, and Erika Milam for their generous and thought-provoking comments. I shall do my best in this space to respond to some of their concerns.

This article examines the critique of the biological species concept advanced by protozoan geneticist Tracy Sonneborn at the 1955 AAAS symposium on "the species problem," published subsequently in 1957. Although Sonneborn was a strong proponent of a population genetical conception of species, he became critical of the biological species concept for its failure to incorporate asexual and obligatory inbreeding organisms. It is argued that Sonneborn's intimate knowledge of the ciliate protozoan Paramecium aurelia species complex brought him into conflict with a (...) growing pressure in the biological sciences to emphasize universal principles of life. Faced with the need to defend the value of P. aurelia as an investigative tool, Sonneborn argued that the sharp break in nature between sexual and asexual organisms posited by proponents of the biological species concept was not an existential feature of the living world, but rather the misleading consequence of an operational definition of species based only upon sexual organisms. Drawing upon his knowledge of the immense variability of P. aurelia, he proposed instead a continuum of breeding systems from obligatory outbreeding to asexual organisms, and a more broadly unifying definition of species that incorporated asexual as well as sexual organisms. Paradoxically, the push for unification that then characterized the evolutionary synthesis served to debar critical consideration of Sonneborn's more unificatory alternative, and his underlying contention that biological anomaly could serve as an important source of conceptual unification. (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)

Ernst Mayr''s historical writings began in 1935 with his essay Bernard Altum and the territory theory and have continued up through his monumentalGrowth of Biological Thought (1982) and hisOne Long Argument: Charles Darwin and the Genesis of Modern Evolutionary Thought (1991). Sweeping in their scope, forceful in their interpretation, enlisted on behalf of the clarification of modern concepts and of a broad view of biology, these writings provide both insights and challenges for the historian of biology. Mayr''s general intellectual formation (...) was guided by the GermanBildung ideal, with its emphasis on synthetic and comprehensive knowledge. His understanding of how to write history was inspired further by the example of the historian of ideas Arthur Lovejoy. Some strengths and limitations of this approach are explored here through attention to Mayr''s treatment of the French biologist J.-B. Lamarck. It is contended that Mayr''s contributions to the history of biology are not restricted to his own very substantial historical writings but also include his encouragement of other scholars, his development of an invaluable archive of scientific correspondence, and his insistence that historians who write about evolution and related subjects acquire an adequate understanding of the principles of Darwinian biology. (shrink)

This paper critically examines the biology of species identity and the morality of crossing species boundaries in the context of emerging research that involves combining human and nonhuman animals at the genetic or cellular level. We begin with the notion of species identity, particularly focusing on the ostensible fixity of species boundaries, and we explore the general biological and philosophical problem of defining species. Against this backdrop, we survey and criticize earlier attempts to forbid crossing species boundaries in the creation (...) of novel beings. We do not attempt to establish the immorality of crossing species boundaries, but we conclude with some thoughts about such crossings, alluding to the notion of moral confusion regarding social and ethical obligations to novel interspecies beings. (shrink)

Morphology and its relevance for systematics is a promising field for the application of biosemiotic principles in scientific practice. Genital coupling in spiders involves very complex interactions between the male and female genital structures. As exemplified by two spider species,Nephila clavipesandNephila pilipes ssp. fenestrata, from a biosemiotic point of view the microstructures of the male bulb’s embolus and the corresponding female epigynal and vulval parts form the morphological zone of an intraspecific communication and sign-interpreting process that is one of the (...) prerequisites for sperm transfer. Hence these morphological elements are of high taxonomic value, as they play an essential role in mating and fertilization and consequently in establishing and preserving a reproductive community. Morphology clearly benefits from a biosemiotic approach, as biosemiotics helps to sort out species-specific morphological characters and to avoid problematic typological interpretations. (shrink)

The allegedly alternative theories of Phyletic Gradualism and Punctuated Equilibria are examined as regards the nature of their differences. The explanatory value of both models is determined by establishing their actual connection with reality. It is concluded that they are to be considered complementary rather than mutually exclusive at all levels of infraspecific, specific, and supraspecific evolution. So, in order to be described comprehensively, the pathways of evolution require at least two distinct models, each based on a discrete range of (...) real phenomena. [Phyletic Gradualism; Punctuated Equilibria; evolutionary theories; divergence models; additive speciation; microevolution; macroevolution; anagenesis.]. (shrink)

Many attempts have been made at supporting either one of the allegedly complementary divergence models Phyletic Gradualism and Punctuated Equilibria by patterns found in specific fossil sequences. However, assessing each model's connection with reality via such “individual case histories” appears not to constitute a relevant approach. Instead, in order to correctly establish the possible merits of both concepts, the claims of each have to be verified against general evolutionary theory. This is being pointed out herein by analyzing cladogenesis at the (...) specific level as an example. [Phyletic Gradualism; Punctuated Equilibria; evolutionary theory; divergence models; case histories; additive speciation.]. (shrink)

Richard Boyd’s Homeostatic Property Cluster Theory is becoming the received view of natural kinds in the philosophy of science. However, a problem with HPC Theory is that it neglects many kinds highlighted by scientific classifications while at the same time endorsing kinds rejected by science. In other words, there is a mismatch between HPC kinds and the kinds of science. An adequate account of natural kinds should accurately track the classifications of successful science. We offer an alternative account of natural (...) kinds that better recognizes the diversity of epistemic aims scientists have for constructing classifications. That account introduces the idea of a classificatory program and provides criteria for judging whether a classificatory program identifies natural kinds. (shrink)

During the 1930s, Aleksandr Promptov—a student of the founder of Russian population genetics Sergei Chetverikov—developed an elaborate concept of speciation in birds. He conducted field investigations aimed at giving a naturalistic content to the theoretical formulations and laboratory models of evolutionary processes advanced within the framework of population genetics, placing particular emphasis on the evolutionary role of bird behavior. Yet, although highly synthetic in combining biogeographical, taxonomic, genetic, ecological, and behavioral studies, Promptov's speciation concept was ignored by the architects of (...) the 1930s and 1940s evolutionary synthesis, including Theodosius Dobzhnasky, Ernst Mayr, and Julian Huxley. In this article, I argue that the story of Promptov's concept and its reception by other evolutionists challenges the traditional presentation of the synthesis as a singular, international process of the unification of biology, which led to the creation of a universal synthetic theory of evolution. It suggests that during the same time period, within largely the same theoretical framework, there were multiple, intrinsically local, attempts at creating synthetic evolutionary concepts. These concepts were often quite particular—in their taxonomic applicability, in their explanations of various evolutionary factors, and in the range of disciplines unified in the synthesis. Apparently, these concepts ran contrary to the universal aspirations of the synthesis architects, and as a result, they were disregarded, first by the architects and later by historians of the evolutionary synthesis. (shrink)

The Evolutionary Synthesis is often seen as a unification process in evolutionary biology, one which provided this research area with a solid common theoretical foundation. As such, neo-Darwinism is believed to constitute from this time onward a single, coherent, and unified movement offering research guidelines for investigations. While this may be true if evolutionary biology is solely understood as centred around evolutionary mechanisms, an entirely different picture emerges once other aspects of the founding neo-Darwinists’ views are taken into consideration, aspects (...) potentially relevant to the elaboration of an evolutionary worldview: the tree of life, the ontological distinctions of the main cosmic entities , the inherent properties of self-organizing matter, evolutionary ethics, and so on. Profound tensions and inconsistencies are immediately revealed in the neo-Darwinian movement once this broader perspective is adopted. This pluralism is such that it is possible to identify at least three distinct and quasi-incommensurable epistemological/metaphysical frameworks as providing a proper foundation for neo-Darwinism. The analysis of the views of Theodosius Dobzhansky, Bernhard Rensch, and Ernst Mayr will illustrate this untenable pluralism, one which requires us to conceive of the neo-Darwinian research agenda as being conducted in more than one research programme or research tradition at the same time. (shrink)

Species pluralism allows for multiple species concepts. Given the overwhelming number of such concepts, this seems like an obvious interpretation of how `species' is used in contemporary biology. But why has it taken so long for this approach to be considered? I argue that part of the reason pluralism was overlooked due to the widespread use of a particular rhetorical strategy developed by Ernst Mayr. This strategy provided a framework for debates about the correct conception of species. That is, the (...) strategy offered a means of comparing modern concepts with a monistic-essentialist understanding of species. I ask what would happen if we replaced this concept with Aristotle's own pluralist-essentialist understanding of species. As recent scholarship shows, Aristotle's philosophy of biology allows for an approach to classification that is in practice highly pluralistic. From this new framework we can understand what sort of assumptions are at stake between modern forms of species pluralism. My analysis shows that the essentialist story told by Mayr and others left us asking the wrong questions about how to conceive of species in an evolutionary world. Having a deeper understanding of Aristotle's approach to the classification of animals allows us to shift focus from the so-called species problem in order to raise four issues that are relevant to current debates. These are questions about: the explanatory power of taxonomic ranks, the importance of the species category problem, whether species are constituted by intrinsic or extrinsic properties, and how to interpret the ``cross-cutting'' metaphor endemic to the pluralist literature. In order to get to these questions I will first explain what sort of claim species pluralism is at the most general level, and a gloss on the standard interpretation of the historical shift from species monism to species pluralism. (shrink)

The dichotomy between ‘typological thinking’ and ‘population thinking’ features in a range of debates in contemporary and historical biology. The origins of this dichotomy are often traced to Ernst Mayr, who is said to have coined it in the 1950s as a rhetorical device that could be used to shield the Modern Synthesis from attacks by the opponents of population biology. In this two-part essay I argue that the origins of the typology/population dichotomy are considerably more complicated and more interesting (...) than is commonly thought. In this first part, I will argue that Mayr's dichotomy was based on two distinct type/population contrasts that had been articulated much earlier by George Gaylord Simpson and Theodosius Dobzhansky. Their distinctions made eminent sense in their own, isolated contexts. In the second part, I will show how Mayr conflated these type/population distinctions and blended in some of his own, unrelated concerns with ‘types’ of a rather different sort. Although Mayr told his early critics that he was merely making “a temporary oversimplification,” he ended up burdening the history and philosophy of biology with a troubled dichotomy. (shrink)

The Committee on Common Problems of Genetics, Paleontology, and Systematics (United States National Research Council) marks part of a critical transition in American evolutionary studies. Launched in 1942 to facilitate cross-training between genetics and paleontology, the Committee was also designed to amplify paleontologist voices in modern studies of evolutionary processes. During coincidental absences of founders George Gaylord Simpson and Theodosius Dobzhansky, an opportunistic Ernst Mayr moved into the project's leadership. Mayr used the opportunity for programmatic reforms he had been pursuing (...) elsewhere for more than a decade. These are evident in the Bulletins he distributed under Committee auspices. In his brief tenure as Committee leader, Mayr gained his first substantial foothold within the coalescing community infrastructure of evolutionary studies. Carrying this momentum forward led Mayr directly into the project to launch the journal Evolution. The sociology of interdisciplinary activity provides useful tools for understanding the Committee's value in the broad sweep of change in evolutionary studies during the synthesis period. (shrink)

Numerous concepts exist for biological species. This diversity of ideas derives from a number of sources ranging from investigative study of particular taxa and character sets to philosophical aptitude and world view to operationalism and nomenclatorial rules. While usually viewed as counterproductive, in reality these varied concepts can greatly enhance our efforts to discover and understand biological diversity. Moreover, this continued "turf war" and dilemma over species can be resolved if the various concepts are viewed in a hierarchical system and (...) each evaluated for its inherent level of consilience. Under this paradigm a theoretically appropriate, highly consilient concept of species capable of colligating the abundant types of species diversity offers the best guidance for developing and employing secondary operational concepts for identifying diversity. Of all the concepts currently recognized, only the non-operational Evolutionary Species Concept corresponds to the requisite parameters and, therefore, should serve as the theoretical concept appropriate for the category Species. As operational concepts, the remaining ideas have been incompatible with one another in their ability to encompass species diversity because each has restrictive criteria as to what qualifies as a species. However, the operational concepts can complement one another and do serve a vital role under the Evolutionary Species Concept as fundamental tools necessary for discovering diversity compatible with the primary theoretical concept. Thus, the proposed hierarchical system of primary and secondary concepts promises both the most productive framework for mutual respect for varied concepts and the most efficient and effective means for revealing species diversity. (shrink)

Speciation is a central but elusive issue in evolutionary biology. Over the past sixty years, the subject has been studied within a framework conceived by Ernst Mayr and Theodosius Dobzhansky and subsequently developed further by numerous other workers. In this “isolation” theory, the evolution of reproductive isolation is a key element of speciation; natural selection is given only secondary importance while gene flow is considered prohibitive to the process. In this paper, I argue that certain elements in this approach have (...) produced confusion and irreconcilability among students of speciation. The more prominent debates in speciation (i.e., the species definition, sympatry/allopatry, and the role of reinforcement) all derive from an inherent conflict between the “isolation” theory and Darwin's “selection” view on species and speciation (in which disruptive selection is crucial). New data, mainly from field ecology, molecular population genetics, laboratory studies with Drosophila and computer analysis, all suggest that the isolation theory may no longer be the most desirable vantage point from which to explore speciation. Instead, environmental selection in large populations, often unimpeded by ongoing gene flow, appears to be the decisive element. The traditional preoccupation with reproductive isolation has created gaps in our knowledge of several crucial issues, mainly regarding the role of environmental selection and its connection with mate selection. BioEssays 22:1134–1141, 2000. © 2000 John Wiley & Sons, Inc. (shrink)

Species are central to biology, but there is currently no agreement on what the adequate species concept should be, and many have adopted a pluralist stance: different species concepts will be required for different purposes. This thesis is a multidimensional analysis of species pluralism. First I explicate how pluralism differs monism and relativism. I then consider the history of species pluralism. I argue that we must re-frame the species problem, and that re-evaluating Aristotle's role in the histories of systematics can (...) shed light on pluralism. Next I consider different forms of pluralism: evolutionary and extra-evolutionary species pluralism, which differ in their stance on evolutionary theory. I show that pluralism is more than a debate about the species category, but a debate about which concepts are legitimate and a claim about how they interact with one another. Following that, I consider what sort of ontology is required for different forms of species pluralism. I argue that pluralists who deny the unity of biology will require a further plurality of frameworks, while those that ground their pluralism in evolution need only one framework. Finally, I consider what pluralism means for biological practice. I argue that species concepts are tools, and reflect on how pluralism can illuminate the way systematists approach the discovery of new species of yeast. Pluralism can make sense of the way species concepts are used, and can be developed to aid researchers in thinking about how to use the right tools for the right jobs. (shrink)

I propose we abandon the unit concept of "the evolutionary synthesis". There was much more to evolutionary studies in the 1920s and 1930s than is suggested in our commonplace narratives of this object in history. Instead, four organising threads capture much of evolutionary studies at this time. First, the nature of species and the process of speciation were dominating, unifying subjects. Second, research into these subjects developed along four main lines, or problem complexes: variation, divergence, isolation, and selection. Some calls (...) for 'synthesis' focused on these problem complexes (sometimes on one of these; other times, all). In these calls, comprehensive and pluralist compendia of plausibly relevant elements were preferred over reaching consensus about the value of particular formulae. Third, increasing confidence in the study of common problems coincided with methodological and epistemic changes associated with experimental taxonomy. Finally, the surge of interest in species problems and speciation in the 1930s is intimately tied to larger trends, especially a shifting balance in the life sciences towards process-based biologies and away from object-based naturalist disciplines. Advocates of synthesis in evolution supported, and were adapting to, these larger trends. (shrink)

Recent discoveries of geographical patterns in microbial distribution are undermining microbiology’s exclusively ecological explanations of biogeography and their fundamental assumption that ‘everything is everywhere: but the environment selects’. This statement was generally promulgated by Dutch microbiologist Martinus Wilhelm Beijerinck early in the twentieth century and specifically articulated in 1934 by his compatriot, Lourens G. M. Baas Becking. The persistence of this precept throughout twentieth-century microbiology raises a number of issues in relation to its formulation and widespread acceptance. This paper will (...) trace the conceptual history of Beijerinck’s claim that ‘everything is everywhere’ in relation to a more general account of its theoretical, experimental and institutional context. His principle also needs to be situated in relationship to plant and animal biogeography, which, this paper will argue, forms a continuum of thought with microbial biogeography. Finally, a brief overview of the contemporary microbiological research challenging ‘everything is everywhere’ reveals that philosophical issues from Beijerinck’s era of microbiology still provoke intense discussion in twenty-first century investigations of microbial biogeography. (shrink)

Ernst Mayr''s scientific career continues strongly 70 years after he published his first scientific paper in 1923. He is primarily a naturalist and ornithologist which has influenced his basic approach in science and later in philosophy and history of science. Mayr studied at the Natural History Museum in Berlin with Professor E. Stresemann, a leader in the most progressive school of avian systematics of the time. The contracts gained through Stresemann were central to Mayr''s participation in a three year expedition (...) to New Guinea and The Solomons, and the offer of a position in the Department of Ornithology, American Museum of Natural History, beginning in 1931. At the AMNH, Mayr was able to blend the best of the academic traditions of Europe with those of North America in developing a unified research program in biodiversity embracing systematics, biogeography and nomenclature. His tasks at the AMNH were to curate and study the huge collections amassed by the Whitney South Sea Expedition plus the just purchased Rothschild collection of birds. These studies provided Mayr with the empirical foundation essential for his 1942Systematics and the Origin of Species and his subsequent theoretical work in evolutionary biology as well as all his later work in the philosophy and history of science. Without a detailed understanding of Mayr''s empirical systematic and biogeographic work, one cannot possibly comprehend fully his immense contributions to evolutionary biology and his later analyses in the philosophy and history of science. (shrink)

The dichotomy between ‘typological thinking’ and ‘population thinking’ features in a range of debates in contemporary and historical biology. The origins of this dichotomy are often traced to Ernst Mayr, who is said to have coined it in the 1950s as a rhetorical device that could be used to shield the Modern Synthesis from attacks by the opponents of population biology. In this two-part essay, I argue that the origins of the typology/population dichotomy are considerably more complicated and more interesting (...) than is commonly thought. In the first part, I argued that Mayr's dichotomy was based on two distinct type/population contrasts that had been articulated much earlier by George Gaylord Simpson and Theodosius Dobzhansky. Their distinctions made eminent sense in their own, isolated contexts. In this second part, I will show how Mayr conflated these type/population distinctions and blended in some of his own, unrelated concerns with ‘types’ of a rather different sort. Although Mayr told his early critics that he was merely making “a temporary oversimplification,” he ended up burdening the history and philosophy of biology with a troubled dichotomy. (shrink)