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)

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)

A far-reaching and influential view in evolutionary biology claims that species are cohesive units held together by gene flow. Biologists have recognized empirical problems facing this view; after sharpening the expression of the view, we present novel conceptual problems for it. At the heart of these problems is a distinction between two importantly different concepts of cohesion, what we call integrative and response cohesion. Acknowledging the distinction problematizes both the explanandum of species cohesion and the (...) explanans of gene flow that are central to the view we discuss. We conclude by tracing four broader implications for the study and conceptualization of species. (shrink)

Species concepts for bacteria and other microbes are contentious, because they are often asexual. There is a Problem of Homogeneity: every mutation in an asexual lineage forms a new strain, of which all descendents are clones until a new mutation occurs. We should expect that asexual organisms would form a smear or continuum. What causes the internal homogeneity of asexual lineages, if they are in fact homogeneous? Is there a natural “species concept” for “microbes”? Two main concepts (...) devised for metazoans and metaphytes have been applied to bacteria. One is the Recombination Concept, a revised form of the Biological Species Concept in which the homogenizing mechanism is the sharing of genome fragments, somewhat akin to sexual recombination. The other is the Ecological Species Concept, in which the ecological niche is that which maintains lineages as cohesive. In this paper I will discuss these two concepts, and offer an underlying model that conjoins them, and consider the implications for species concepts in general. In short, my argument is that asexual species are instances of the most primitive and underived notion of species, which I will call “quasispecies”, following Eigen, and that sexual species are merely one derived kind of species. Moreover, I will argue that there is a continuum of recombination from simple viral models in which each strain is a clone, through to obligate recombination of 50% of the parents’ genome, and that consequently there is no sharp division between “microbial” and more familiar species. (shrink)

The so-called ‘‘species problem’’ has plagued evolution- ary biology since before Darwin’s publication of the aptly titled Origin of Species. Many biologists think the problem is just a matter of semantics; others complain that it will not be solved until we have more empirical data. Yet, we don’t seem to be able to escape discussing it and teaching seminars about it. In this paper, I briefly examine the main themes of the biological and philosophical liter- atures on the (...) species problem, focusing on identifying common threads as well as relevant differences. I then argue two fundamental points. First, the species problem is not primarily an empirical one, but it is rather fraught with philosophical questions that require—but cannot be settled by—empirical evidence. Second, the (dis-)solution lies in explicitly adopting Wittgenstein’s idea of ‘‘family resemblance’’ or cluster concepts, and to consider spe- cies as an example of such concepts. This solution has several attractive features, including bringing together apparently diverging themes of discussion among bio- logists and philosophers. The current proposal is con- ceptually independent (though not incompatible) with the pluralist approach to the species problem advocated by Mishler, Donoghue, Kitcher and Dupre ́, which implies that distinct aspects of the species question need to be emphasized depending on the goals of the researcher. From the biological literature, the concept of species that most closely matches the philosophical discussion pre- sented here is Templeton’s cohesion idea. (shrink)

This paper isolates a hard, long-standing species problem: developing a comprehensive and exacting theory about the constitutive conditions of the species category, one that is accurate for most of the living world, and which vindicates the widespread view that the species category is of more theoretical import than categories such as genus, sub-species, paradivision, and stirp. The paper then uncovers flaws in several views that imply we have either already solved that hard species problem or (...) dissolved it altogether – so-called We Are Done views. In doing so the paper offers new criticisms of the general lineage species concept (GLSC), evolutionary species concept (EvSC), biological species concept (BSC), other similar concepts, Ereshefsky’s eliminative pluralism about the species category, and both Mishler’s pessimism and Wilkins’ phenomenalism about that category. Opposed to We Are Done views, the paper argues for a Revving Up view, on which we are nearly ready to begin the hard species problem in earnest. To help work towards these conclusions, the paper begins with an outline of a new kind of view of species (Barker 2019a), which proposes they are feedback systems of a mathematically specifiable and empirically testable sort. (shrink)

There is no question that the constituents of cells and organisms are joined together by the part-whole relation. Genes are part of cells, and cells are part of organisms. Species taxa, however, have traditionally been conceived of, not as wholes with parts, but as classes with members. But why does the relation change abruptly from part-whole to class-membership above the level of organisms? Ghiselin, Hull and others have argued that it doesn't. Cells and organisms are cohesive mereological sums, and (...) since species taxa are like cells and organisms in the relevant respects, they, too, are cohesive mereological sums. I provide further reasons in support of the thesis that species are mereological sums. I argue, moreover, that the advocate of this thesis is committed to a form of pluralism with respect to the species concept. (shrink)

Pluralisms of various sorts are popular in philosophy of science, including those that imply some scientific concept x should be eliminated from science in favour of a plurality of concepts x1, x2, … xn. This article focuses on influential and representative arguments for such eliminative pluralism about the concept species. The main conclusions are that these arguments fail, that all other extant arguments also fail, and that this reveals a quite general dilemma, one that poses a defeasible (...) presumption against many eliminative pluralisms about various scientific concepts. The article ends by outlining a novel integrative alternative in defence of species. 1) Introduction 2) The species Concept, the Category ‘Species’, and the ‘Species’ Category Problem 3) What Are Eliminative Pluralism about species, and the Arguments for It? 4) Evaluation of Arguments 4.1 Splitting? 4.2 Lumping? 4.3 The eliminative pluralist’s dilemma 5) More General Lessons6Species Cohesion: An Integrative Alternative7Conclusion. (shrink)

This paper proposes a new and testable view about the nature of species and other evolving lineages, according to which they are feedback systems. On this view, it is a mistake to think gene flow, niche sharing, and trait frequency similarities between populations are among variables that interact to cause some further downstream variable that distinguishes evolving lineages from each other, some sort of “species cohesion” for example. Instead, gene flow, niche sharing, similarities between populations, and other (...) causal variables feed into each other—instances of these at earlier times help cause instances of these same variables at later times. And any lineage-identifying cohesion just is the recurrence or cycling of these feedback relations within metapopulations over generations. Such cohesion can then be represented as variable M within multi-dimensional variable spaces, where values of M vary dynamically with the frequency and magnitude of feedback relations. Related conditions for being a species or other evolving lineage are then clarified. To argue for the development and testing of this view, the paper shows how it improves upon others. (shrink)

Different concepts define species at the pattern-level grouping of organisms into discrete clusters, the level of the processes operating within and between populations leading to the formation and maintenance of these clusters, or the level of the inner-organismic genetic and molecular mechanisms that contribute to species cohesion or promote speciation. I argue that, unlike single-level approaches, a multi-level framework takes into account the complex sequences of cause-effect reinforcements leading to the formation and maintenance of various patterns, and (...) allows for revisions and refinements of pattern-based characterizations in light of the gradual elucidation of the causes and mechanisms contributing to pattern formation and maintenance. (shrink)

There are a number of different species concepts currently in use. The variety results from differing desiderata and practices of taxonomists, ecologists and evolutionary theorists. Recently, arguments have been presented for pluralism about species. I believe this is unsatisfactory, however, because of the central role of species in biological theory. Taking the line that species are individuals, I ask what might individuate them. In other work I have argued that dynamical systems are individuated by their (...) class='Hi'>cohesion. I present here a version of a cohesion concept of species that accounts for the advantages of other species concepts, and is open-ended enough to accommodate additions to or changes in biological theory. On my account biological forces combine like Newtonian forces, to work on a common locus. Just as we might have an electromagnetic system, we might have an ecological species, if the dominant source of cohesion is ecology, but there is no certainty that biological species will divide up into elegant single principle types anymore than there is for physical systems. (shrink)

Samir Okasha argues that clade selection is an incoherent concept, because the relation that constitutes clades is such that it renders parent-offspring (reproduction) relations between clades impossible. He reasons that since clades cannot reproduce, it is not coherent to speak of natural selection operating at the clade level. We argue, however, that when species-level lineages and clade-level lineages are treated consistently according to standard cladist commitments, clade reproduction is indeed possible and clade selection is coherent if certain conditions (...) obtain. Despite clade selection's logical coherence, however, we share some of Okasha's pessimism. Whether or not clades are a unit of selection is ultimately a question of empirical support and theoretical import. (shrink)

Frank E. Zachos offers a comprehensive review of one of today's most important and contentious issues in biology: the species problem. After setting the stage with key background information on the topic, the book provides a brief history of species concepts from antiquity to the Modern Synthesis, followed by a discussion of the ontological status of species with a focus on the individuality thesis and potential means of reconciling it with other philosophical approaches. More than 30 different (...) species concepts found in the literature are presented in an annotated list, and the most important ones, including the Biological, Genetic, Evolutionary and different versions of the Phylogenetic Species Concept, are discussed in more detail. Specific questions addressed include the problem of asexual and prokaryotic species, intraspecific categories like subspecies and Evolutionarily Significant Units, and a potential solution to the species problem based on a hierarchical approach that distinguishes between ontological and operational species concepts. A full chapter is dedicated to the challenge of delimiting species by means of a discrete taxonomy in a continuous world of inherently fuzzy boundaries. Further, the book outlines the practical ramifications for ecology and evolutionary biology of how we define the species category, highlighting the danger of an apples and oranges problem if what we subsume under the same name ("species") is in actuality a variety of different entities. A succinct summary chapter, glossary and annotated list of references round out the coverage, making the book essential reading for all biologists looking for an accessible introduction to the historical, philosophical and practical dimensions of the species problem. (shrink)

Many phylogenetic systematists have criticized the Biological Species Concept (BSC) because it distorts evolutionary history. While defenses against this particular criticism have been attempted, I argue that these responses are unsuccessful. In addition, I argue that the source of this problem leads to previously unappreciated, and deeper, fatal objections. These objections to the BSC also straightforwardly apply to other species concepts that are not defined by genealogical history. What is missing from many previous discussions is the fact (...) that the Tree of Life, which represents phylogenetic history, is independent of our choice of species concept. Some species concepts are consistent with species having unique positions on the Tree while others, including the BSC, are not. Since representing history is of primary importance in evolutionary biology, these problems lead to the conclusion that the BSC, along with many other species concepts, are unacceptable. If species are to be taxa used in phylogenetic inferences, we need a history-based species concept. (shrink)

This chapter defends a pluralist understanding of species on which a normative species concept is viable and can support natural goodness evaluations. The central question here is thus: Since organisms are to be evaluated as members of their species, how does a proper understanding of species affect the feasibility of natural goodness evaluations? Philippa Foot has argued for a form of natural goodness evaluation in which living things are evaluated by how well fitted they are (...) for flourishing as members of their species, in ways characteristic of their species. She has further argued that assessments of moral goodness in humans are of the same evaluative form. However, natural goodness evaluations and, by extension, the natural goodness approach, do not garner justification in virtue of employing a scientifically privileged conception of species. The natural goodness approach is only justified given particular metaethical and normative commitments that are independent of naturalism, since the approach does not depend upon naturalism alone. (shrink)

Species are the basis of the taxonomic scheme. They are the lowest taxonomic category that are used as units for describing biodiversity and evolution. In this contribution we discuss the current species concept for prokaryotes. Such organisms are considered to represent the widest diversity among living organisms. Species is currently circumscribed as follows: A prokaryotic species is a category that circumscribes a (preferably) genomically coherent group of individual isolates/strains sharing a high degree of similarity in (...) (many) independent features, comparatively tested under highly standardized conditions. Although the number of described prokaryotic species is underrepresented in the living world, this phylo-phenetic or polythetic species concept currently in use is considered to be pragmatic, operational and universally applicable and successfully used for identification processes. (shrink)

The species concept is one of the oldest and most fundamental in biology. And yet it is almost universally conceded that no satisfactory definition of what constitutes a species has ever been proposed. The present article is devoted to an attempt to review the status of the problem from a methodological point of view. Since the species is one of the many taxonomic categories, the question of the nature of these categories in general needs to be (...) entered into. (shrink)

Species are the basis of the taxonomic scheme. They are the lowest taxonomic category that are used as units for describing biodiversity and evolution. In this contribution we discuss the current species concept for prokaryotes. Such organisms are considered to represent the widest diversity among living organisms. Species is currently circumscribed as follows: A prokaryotic species is a category that circumscribes a (preferably) genomically coherent group of individual isolates/strains sharing a high degree of similarity in (...) (many) independent features, comparatively tested under highly standardized conditions. Although the number of described prokaryotic species is underrepresented in the living world, this phylo-phenetic or polythetic species concept currently in use is considered to be pragmatic, operational and universally applicable and successfully used for identification processes. (shrink)

Students of later medieval semantics are familiar with the controversy that developed at the end of the thirteenth century over the signification of names. The debate focused on the signification of common nouns such as ‘man’ and ‘animal’: Do they signify an extramental thing or a mental representation of an extramental thing?Some authors at the end of the thirteenth century also discussed another question concerning what names signify, that is, whether they signify the composite of matter and form or only (...) the form of the composite. This second debate will not be considered in this article. Duns Scotus is commonly recognized as having played an important role in this debate.See Costantino Marmo, “Ontology and Semantics in the Logic of Duns Scotus,” in Umberto Eco and Costantino Marmo, ed., On Medieval Theory of Signs, (Amsterdam and Philadelphia: John Benjamins, 1989), pp. 161–63; and esp. Dominik Perler, “Duns Scotus on Signification,” Medieval Philosophy and Theology 3 (1993): 97–120. On the topic in general, see Paul Vincent Spade, “The Semantics of Terms,” in N. Kretzmann, A. Kenny, J. Pinborg, eds., The Cambridge History of Later Medieval Philosophy (Cambridge: Cambridge U.P., 1982), pp. 188–90; Jan Pinborg, “Bezeichnung in der Logik des XIII. Jahrhunderts,” in Albert Zimmermann, ed., Der Begriff der Repraesentatio im Mittelalter, Miscellanea Mediaevalia 8 (Berlin and New York: de Gruyter, 1971): 238–81; Elizabeth J. Ashworth, “Signification and Modes of Signifying in Thirteenth-Century Logic: A Preface to Aquinas on Analogy,” Medieval Philosophy and Theology 1 (1991): 43–53; Claude Panaccio, “From Mental Word to Mental Language,” Philosophical Topics 20 (1992): 125–47. In his Ordinatio, he alludes to a magna altercatio among his contemporaries concerning signification.John Duns Scotus, Ordinatio 1.27.1–3 n.83, in Commissio Scotistica, ed, Opera omnia 6 (Vatican City: Typis Polyglottis, 1963), p. 97. What is more, he gives, in his two commentaries on Aristotle’s Peri hermeneias, a detailed and fair analysis of the two contrasting positions on this issue.John Duns Scotus, Super Peri hermeneias 1.2, and Super Peri hermeneias 2.1, in Opera omnia 1 (Paris: L. Vivès, 1891), pp. 540–44, 582–85. Scotus’s logical commentaries are usually thought to have been composed before his theological writings, in the last decade of the thirteenth century. (shrink)

The nature of science is a primary goal in school science. Most teachers are not well-prepared for teaching NOS, but a sophisticated and in-depth understanding of NOS is necessary for effective teaching. Some authors emphasize the need for teaching NOS in context. Species, a central concept in biology, is proposed in this article as a concrete example of a means for achieving increased understanding of NOS. Although species are commonly presented in textbooks as fixed entities with a (...) single definition, the concept of species is a highly discussed one in the science and the philosophy of biology. A multitude of species concepts exist, reflecting both the views and interests of researchers and their utility in different organism groups. The present study serves to address the following questions: How do textbooks in Norwegian primary and lower secondary schools present the concept of species? Can inquiries into the concept of “species” serve to highlight aspects of NOS? A review of the available literature on species and species concepts in school is also performed. In the schoolbooks, the biological species concept is commonly used as the main definition, whereas the morphological species concept is represented by additional remarks of similarity. The potential and pitfalls of using the species concept for teaching NOS are discussed, with NOS being discussed both as a family resemblance concept and as a consensus list. Teacher education is proposed as a starting point for inducing a more sophisticated view of biology into schools. (shrink)

Integration (interaction among parts of an entity) is suggested to be necessary for individuality (contra, Metaphysics and the Origin of Species). A synchronic species is an integrated individual that can evolve as a unified whole; a diachronic lineage is a non-integrated historical entity that cannot evolve. Synchronic species and diachronic lineages are consequently suggested to be ontologically distinct entities, rather than alternative perspectives of the same underlying entity (contra Baum (1998), Syst. Biol. 47, 641–653; de Queiroz (1995), (...) Endless Forms: Species and Speciation, pp. 57–75; Genes, Categories and Species). Species concepts usually refer to either one or the other entity; for instance, the Biological Species Concept refers to synchronic species, whereas the Cladistic Species Concept refers to diachronic lineages. The debate over species concepts has often failed to recognise this distinction, resulting in invalid comparisons between definitions that attempt to delineate fundamentally different entities. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Reviewed by:Aristotle on the Concept of Shared Life by Sara BrillZoli FilotasSara Brill. Aristotle on the Concept of Shared Life. Oxford: Oxford University Press, 2020. Pp. 304. Hardback, $100.00.This book is a sweeping survey of Aristotle's approach to human life. It covers what might seem to be an idiosyncratic set of topics: friendship, animal behavior, commerce, tyranny, and motherhood are among the more prominent. But Sara Brill (...) pulls them together into a cohesive and illuminating picture, showing how each reflects Aristotle's conception of the concept "life" and the two Greek words, zôê and bios, that he uses to discuss it.The book rebukes thinkers who draw too sharp a contrast between animal life, on the one hand, and human politics, on the other. Until recently, Brill writes, that has been the dominant trend, uniting thinkers otherwise as different as Giorgio Agamben and David Keyt. For writers like them, human beings must overcome and sublimate their base, animal instincts (zôê, "mere life") in order to develop rational, uniquely human "ways of life" (bioi) like the lives of the citizen and the philosopher.For Brill, by contrast, the relationship between a person and the polis in Aristotle is "an intensified form of the relations between any animal and its proper habitat" (29). Indeed, every animal species has a distinctive way of life, a bios. The lavish discussion of animal "personality" or "character" (ethos) in the History of Animals suggests their range: lions are brave, cattle are stupid, dolphins are gentle, and so on. A personality not only helps an animal flourish in some habitat (topos) but also defines its relationships with other members of its species. So although Aristotle only classifies a few animal species as "political," Brill reminds us that there is a clear sense in which all are social.Aristotle famously claims that we humans are the "most political" of all animals, but Brill shows that this claim is both incomplete and misleading. For although Aristotle thinks that we outdo even bees in organized cooperation, he also stresses that we outdo even "warlike" eagles in our capacity for violence and solitude. Confronted with the opposition between solitary and gregarious ways of life, human beings "dualize" or "play a double game" (epamphoterizei) (HA I.1, 488a7). That is, much as frogs have water-dwelling and land-dwelling inclinations, humans are socially amphibious. Indeed, every human behavior—communal, solitary, and contentious alike—turns out to be an expression of animal nature. Brill points out that much of the Politics emphasizes the negative, the way that human beings make their own and each other's lives unlivable. Thus, although Aristotle embraces the sweetness of life, which has a distinct and intrinsic pleasure, his political project anticipates Nietzsche in squarely and unflinchingly studying its "horrors" (254).For Brill, the apex of human sociality in Aristotle is not politics but the so-called "perfect" friendship that Aristotle describes in Nicomachean Ethics VIII–IX and Eudemian Ethics VII. Perfect friends, Aristotle says repeatedly, "share a life" (suzên, cognate with zôê rather than bios). Friends grieve and rejoice together, perceive together, and philosophize together too. Brill emphasizes that this list includes the full range of psychic functions, from appetite all the way up to the highest forms of abstract thought. As they live together, friends build up a "nexus of meaning and value," a "world as it is created through the sharing of pleasure, judgment, and action" in which there "emerges a subjectivity which cannot be easily or simply conceived as 'mine'" (43, emphasis in original). In the best kinds of friendship, we realize that human life is lived by the partnership itself, not just the friends individually. [End Page 149]But Brill stresses that Aristotle thinks few people will ever find "perfect friendship." It is completely out of reach for most citizens of any real-world city. Yet for Aristotle, the flawed and diverse citizens of every polis nevertheless engage in a form of shared life: shared perception of the just and unjust. How is that possible? Through fragile institutions and customs, what Aristotle calls an "adornment of habits and an arrangement of correct laws" (Politics II.5... (shrink)

Summary The common view has been that Darwin regarded species as artificial and arbitrary constructions of taxonomists, not as distinct natural units. However, in his transmutation notebooks he clearly subscribed to the reality of species, on the basis of the criterion of non-interbreeding. A consequence of this biological species concept was his identification of the acquisition of reproductive isolation as the mark of the completion of speciation. He developed in the notebooks a theory of geographic speciation (...) on the grounds of (a) an empirical correlation between barriers and the geographical distributions of allied species, (b) the analogy of artificial isolation in the formation of new domesticated varieties, and (c) the logical consequence of blending inheritance. A brief discussion of Darwin's species concept in later writings concludes the paper. (shrink)

The biological species (biospecies) concept applies only to sexually reproducing species, which means that until sexual reproduction evolved, there were no biospecies. On the universal tree of life, biospecies concepts therefore apply only to a relatively small number of clades, notably plants andanimals. I argue that it is useful to treat the various ways of being a species (species modes) as traits of clades. By extension from biospecies to the other concepts intended to capture the (...) natural realities of what keeps taxa distinct, we can treat other modes as traits also, and so come to understand that theplurality of species concepts reflects the biological realities of monophyletic groups.We should expect that specialists in different organisms will tend to favour those concepts that best represent the intrinsic mechanisms that keep taxa distinct in their clades. I will address the question whether modes ofreproduction such as asexual and sexual reproduction are natural classes, given that they are paraphyletic in most clades. (shrink)

The longstanding species problem in biology has a history that suggests a solution, and that history is not the received history found in many texts written by biologists or philosophers. The notion of species as the division into subordinate groups of any generic predicate was the staple of logic from Aristotle through the middle ages until quite recently. However, the biological species concept during the same period was at first subtly and then overtly different. Unlike the (...) logic sense, which relied on definitions of the essence of both genus and species, biological species from the time of Epicurus were consistently considered to involve a reproductive element: in short, living species relied not on essential definitions, but on the generative cause, which might not be definable. I term this the generative conception of species: species were the generation by reproduction of form. This undercuts the claim that species before Darwin were essentialist, and divorces the notion of a type from that of essence. In fact, as late as the end of the nineteenth century, logicians explicitly treated biological “species” as a homonym only of logical essentialist species, and permitted considerable deviation from the type or form. At every point, species in logic were thought to be a subset, in effect, of some more general notion. I sketch a history of both philosophical and biological traditions of the species concept, before turning to the current conceptions. These are reconsidered in the light of this history, and in particular Mayr’s changing views are shown to be somewhat Whiggish, historiographically. Of the many touted biological species concepts, only one of which (Mayr’s) is called _the_ Biological Species Concept, none appears to capture all the relevant facts, intuitions, and operational requirements of biology. Cladistic conceptions, however, have much in common with the older philosophical literature, in that the natural group of cladism is the clade, or monophyletic group. After considering the Individuality Thesis, and the metaphysics of species, we see that species are the most particular terminal taxa in a clade, and that they are “defined” in terms of the particular synapomorphies, or evolved characters, that are causally responsible for keeping the lineages that organisms form distinct from one another. In this way, we can remain within the generative conception of species that has been in play for over two millennia, and yet avoid the pitfalls of prior attempts to find a universal conception of species. (shrink)

The phylogenetic species concept is applied for the first time to a major radiation of birds, the birds-of-paradise (Paradisaeidae) of Australasia. Using the biological species concept, previous workers have postulated approximately 40–42 species in the family. Of these, approximately 13 are monotypic and 27 are polytypic with about 100 subspecies. Phylogenetic species are irreducible (basal) clusters of organisms (terminal taxa) that are diagnosably distinct from other such clusters. Within the context of this concept, (...) approximately 90 species of paradisaeids are postulated to have diversified within Australasia. The phylogenetic species concept more accurately describes evolutionary diversity within the family and provides a better theoretical and empirical framework for analysing speciation, historical biogeography and patterns of morphological, behavioral and ecological diversification within this group than does the biological species concept. (shrink)

A natural starting place for developing a phylogenetic species concept is to examine monophyletic groups of organisms. Proponents of “the” Phylogenetic Species Concept fall into one of two camps. The first camp denies that species even could be monophyletic and groups organisms using character traits. The second groups organisms using common ancestry and requires that species must be monophyletic. I argue that neither view is entirely correct. While monophyletic groups of organisms exist, they should (...) not be equated with species. Instead, species must meet the more restrictive criterion of being genealogically exclusive groups where the members are more closely related to each other than to anything outside the group. I carefully spell out different versions of what this might mean and arrive at a working definition of exclusivity that forms groups that can function within phylogenetic theory. I conclude by arguing that while a phylogenetic species concept must use exclusivity as a grouping criterion, a variety of ranking criteria are consistent with the requirement that species can be placed on phylogenetic trees. (shrink)

Édouard Le Roy as early as 1901 observed the existence of an intellectual movement seeking to break from traditional positivism and set for himself the task of drawing up the program of this new positivism. Noting that this program precedes the Vienna Circle, I endeavor to determine its nature and to evaluate its impact on logical positivism. Viewed in this light, the discussions between Le Roy, Poincaré and Duhem appear more prolonged and substantial than is usually thought. What we have (...) here is perhaps not a homogeneous doctrine but a vigorous intellectual movement, from which logical positivists were able to borrow specific theses in their attempts to mitigate Mach's strict positivism; more important still, they had before them an example of neopositivism. History is not the only concern: among the issues debated, one encounters the claim that facts are theory-laden. This claim still stirs controversy today. An inquiry into the origins of the claim is one way of clarifying the arguments involved. (shrink)