Interactions with yellowjackets offer opportunities to reflect on what it is to encounter radical alterity and the conditions that are necessary for the limited empathy such encounters afford us. Effort must be made to set aside automatic judgments, and neither simulation nor theorizing can be sufficient to give us reliable insights, but mindful attentiveness can at least help us attend to the possibilities of interaction and tentative interpretation.

We argue that C. Darwin and more recently W. Hennig worked at times under the simplifying assumption of an eternal biosphere. So motivated, we explicitly consider the consequences which follow mathematically from this assumption, and the infinite graphs it leads to. This assumption admits certain clusters of organisms which have some ideal theoretical properties of species, shining some light onto the species problem. We prove a dualization of a law of T.A. Knight and C. Darwin, and sketch a decomposition result (...) involving the internodons of D. Kornet, J. Metz and H. Schellinx. A further goal of this paper is to respond to B. Sturmfels’ question, “Can biology lead to new theorems?”. (shrink)

Marc Ereshefsky argues that pluralism about species suggests that the species concept is not theoretically useful. It is to be abandoned in favor of several concrete species concepts that denote real categories. While accepting species pluralism, the present paper rejects eliminativism about the species category. It is argued that the species concept is important and that it is possible to make sense of a general species concept despite the existence of different concrete species concepts.

Ernst Mayr's typological/population distinction is a conceptual thread that runs throughout much of his work in systematics, evolutionary biology, and the history and philosophy of biology. Mayr himself claims that typological thinking originated in the philosophy of Plato and that population thinking was first introduced by Charles Darwin and field naturalists. A more proximate origin of the typological/population thinking, however, is found in Mayr's own work on species. This paper traces the antecedents of the typological/population distinction by detailing Mayr's changing (...) views of species between 1942 and 1955. During this period, Mayr struggles to refine the biological species concept in the face of tensions that exist between studying species locally and studying them as geographically distributed collections of variable populations. The typological/population distinction is first formulated in 1955, when Mayr generalizes from the type concept versus the population concept in taxonomy to typological versus population thinking in biology more generally. Mayr's appeal to the more general distinction between typological and population thinking coincides with the waning status of natural history and evolutionary biology that occurs in the early 1950s and the distinction plays an important role in Mayr's efforts to legitimate the natural historical sciences. (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)

Biologists and philosophers that debate the existence of the species category are split into two main camps. Some believe that the species category does not exist and that the term ‘species’ should be junked. Others believe that given new biological insights and the application of philosophical ideas, we can show that the species category does exist. This paper charts a position between skeptics and defenders of the species category. That position holds that the species category does not exist, yet those (...) taxa we call ‘species’ do exist. And, despite skepticism over the species category, there are pragmatic reasons to keep the word ‘species.’ This approach to the species category is far from new, for it is the one that Darwin suggested. Hence it is dubbed ‘Darwin’s solution to the species problem.’. (shrink)

Homeostatic Property Cluster (HPC) theory suggests that species and other biological taxa consist of organisms that share certain similarities. HPC theory acknowledges the existence of Darwinian variation within biological taxa. The claim is that “homeostatic mechanisms” acting on the members of such taxa nonetheless ensure a significant cluster of similarities. The HPC theorist’s focus on individual similarities is inadequate to account for stable polymorphism within taxa, and fails properly to capture their historical nature. A better approach is to treat distributions (...) of traits in species populations as irreducible facts, explained in terms of selection pressures, genealogy, and other evolutionary factors. We call this view Population Structure Theory (PST). PST accommodates the view, implicit in biological systematics, that species are identified by reference to particular historical populations. (shrink)

Philosophical discussions of species have focused on multicellular, sexual animals and have often neglected to consider unicellular organisms like bacteria. This article begins to fill this gap by considering what species concepts, if any, apply neatly to the bacterial world. First, I argue that the biological species concept cannot be applied to bacteria because of the variable rates of genetic transfer between populations, depending in part on which gene type is prioritized. Second, I present a critique of phylogenetic bacterial species, (...) arguing that phylogenetic bacterial classification requires a questionable metaphysical commitment to the existence of essential genes. I conclude by considering how microbiologists have dealt with these biological complexities by using more pragmatic and not exclusively evolutionary accounts of species. I argue that this pragmatism is not borne of laziness but rather of the substantial conceptual problems in classifying bacteria based on any evolutionary standard. (shrink)

I argue that defenders of general duties of species preservation are faced with an impossible task. I distinguish derivative from non-derivative value and argue that the derivative value of species can yield only limited and contingent duties of preservation. There can be no general duty of species preservation unless all species have non-derivative value. Ongoing controversy over the ’species’ notion has not deterred some from claiming settled authority for whatever notion appears most conducive to their favored account of species value. (...) This is a mistake. The actual task is to state biologically plausible criteria for a ’species’ notion and to make the case that these criteria demarcate something of moral value. I argue that the task is made impossible by the same basic biological facts that led Darwin to the view that species are “merely artificial combinations made for convenience.‘. (shrink)

Species serve as both the basic units of macroevolutionary studies and as the basic units of taxonomic classification. In this paper I argue that the taxa identified as species by the Phylogenetic Species Concept (Mishler and Brandon 1987) are the units of biological organization most causally relevant to the evolutionary process but that such units exist at multiple levels within the hierarchy of any phylogenetic lineage. The PSC gives us no way of identifying one of these levels as the privileged (...) level on which taxonomic classifications can be based. (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)

What Is Biodiversity? is a theoretical and conceptual exploration of the biological world and how diversity is valued. Maclaurin and Sterelny explore not only the origins of the concept of biodiversity, but also how that concept has been shaped by ecology and more recently by conservation biology. They explain the different types of biodiversity important in evolutionary theory, developmental biology, ecology, morphology and taxonomy and conclude that biological heritage is rich in not just one biodiversity but many. Maclaurin and Sterelny (...) also explore the case for the conservation of these biodiversities using option value theory, a tool borrowed from economics. (shrink)

The correct explanation of why species, in evolutionary theory, are individuals and not classes is the cladistic species concept. The cladistic species concept defines species as the group of organisms between two speciation events, or between one speciation event and one extinction event, or (for living species) that are descended from a speciation event. It is a theoretical concept, and therefore has the virtue of distinguishing clearly the theoretical nature of species from the practical criteria by which species may be (...) recognized at any one time. Ecological or biological (reproductive) criteria may help in the practical recognition of species. Ecological and biological species concepts are also needed to explain why cladistic species exist as distinct lineages, and to explain what exactly takes place during a speciation event. The ecological and biological species concepts work only as sub-theories of the cladistic species concept and if taken by themselves independently of cladism they are liable to blunder. The biological species concept neither provides a better explanation of species indivudualism than the ecological species concept, nor, taken by itself, can the biological species concept even be reconciled with species individualism. Taking the individuality of species seriously requires subordinating the biological, to the cladistic, species concept. (shrink)

The purpose of this paper is to test the contemporary concept of biological species against some of the problems caused by treating species as spatiotemporally extended entities governed by criteria of persistence, identity, etc. After outlining the general problem of symmetric division in natural objects, I set out some useful distinctions (section 1) and confirm that species are not natural kinds (section 2). Section 3 takes up the separate issue of species definition, focusing on the Biological Species Concept (BSC). Sections (...) 4 and 5 examine the matter of species identity over space and time respectively, as determined by the BSC. Both gradualistic and punctuated equilibrium models of speciation are discussed. In section 6 I argue that the BSC fails to determine adequate criteria for dealing with certain kinds of speciation. Section 7 moves speculatively beyond the BSC to a brief examination of alternatives. (shrink)

RESUMEN: La biología evolucionista no ha logrado definir un concepto de especie que satisfaga a todos sus colaboradores. El presente panorama crítico de las principales propuestas y sus respectivas dificultades apunta, por un lado, a ilustrar los procesos de formación de conceptos en las ciencias empíricas y, por otro, a socavar la visión parateológica del conocimiento y la verdad que inspiró inicialmente a la ciencia moderna y prevalece aún entre muchas personas educadas. El artículo se divide en dos partes. La (...) primera atiende al concepto biológico (o genético) de especie adoptado por Theodosius Dobzhansky y Ernst Mayr alrededor de 1940, así como a las alternativas introducidas para superar sus limitaciones. La segunda parte estudia la tradición “cladista” fundada por Willi Hennig (1950) y sus ramificaciones. Varios conceptos de especie que no era fácil integrar en estos dos grupos se omitieron en aras de la coherencia y la brevedad de la exposición.ABSTRACT: Evolutionary biology has not suceeded in defining a concept of species that will satisfy all researchers. This critical survey of the main proposals and their respective difficulties tends, on the one hand, to throw light on the processes of concept formation in the empirical sciences, and, on the other, to undermine the paratheological vision of knowledge and truth that initially inspired modern science and still prevails among many educated persons. The article is divided into two parts. The first part concerns the biological (or genetical) concept of species which was adopted by Theodosius Dobzhansky and Ernst Mayr ca. 1940 and some alternatives which were subsequently introduced to overcome its limitations. The second part deals with several branches of the cladist tradition founded by Willi Hennig (1950). Various concepts of species that could not be easily integrated in either group were omitted for the sake of coherence and brevity. (shrink)

The project of this paper is to understand what a phylogenetic tree represents and to discuss some of the implications that this has for the practice of systematics. At least the first part of this task, if not both parts, might appear trivial—or perhaps better suited for a single page in a textbook rather than a scholarly research paper. But this would be a mistake. While the task of interpreting phylogenetic trees is often treated in a trivial way, their interpretation (...) is tied to foundational conceptual questions at the heart of systematics—questions whose answers are hotly disputed. I have previously argued that widely shared ideas about the meaning and interpretation of phylogenetic trees are inconsistent with species concepts other than some genealogical version of a phylogenetic species concept (Velasco 2008). Here I rely on a similar approach and concentrate on the implications of the necessary conditions underlying the inferences that we make using phylogenetic trees. I argue that common practices for the interpretation and use of trees are in conflict and that unacceptable principles about species as units of phylogeny must be given up. According to the view that I will develop, all phylogenetic trees depict the history of populations. The branches on trees represent collections of population lineages through time and the splits represent population lineage splits. This is true regardless of whether the tips of the trees are themselves populations, or are species or higher taxa. Although this conclusion might be paired naturally with a view that species must be monophyletic groups, this population-centric view of trees is independent of that view of species. If we still want to have species that are paraphyletic groups of populations, this is permissible as long as we also do not treat species as the units of phylogeny. This population-centric view opposes a species-centric view of phylogeny and might be called a “rank-free” approach since it entails that we do not need to determine which groups are species (which is partly a ranking question) in order to build a tree. This conclusion and the argument for it are meant to be consistent with, but not require, acceptance of the conclusions of Velasco (2008) regarding species. (shrink)

A common view is that species occupy a unique position on the Tree of Life. Evaluating this claim requires an understanding of what the Tree of Life represents. The Tree represents history, but there are at least three biological levels that are often said to have genealogies: species, organisms, and genes. Here I focus on defending the plausibility of a gene-based account of the Tree. This leads to an account of species that are determined by gene genealogies. On this view, (...) an exclusive group is a group of organisms that forms a clade for a higher proportion of the genome than any conflicting clade. Taxa occupy a unique position in what can be called the ‘primary concordance tree’. But each gene has its own historical ‘Tree of Life’. I conclude by arguing that both organismal pedigrees with their corresponding Tree as well as gene genealogies and their trees are objectively real and play important, but different, roles in biological practice. (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)

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)

Defining Species: A Sourcebook from Antiquity to Today provides excerpts and commentary on the definition of «species from source material ranging from the ...

"--Joel Cracraft, American Museum of Natural History "This is not the potted history that one usually finds in texts and review articles.

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)

Speciation is an aspect of evolutionary biology that has received little philosophical attention apart from articles mainly by biologists such as Mayr (1988). The role of speciation as a terminus a quo for the individuality of species or in the context of punctuated equilibrium theory has been discussed, but not the nature of speciation events themselves. It is the task of this paper to attempt to bring speciation events into some kind of general scheme, based primarily upon the work of (...) Sergey Gavrilets on adaptive landscapes, using migration rate, or gene flow, as the primary scale, and concluding that adaptive and drift explanations are complementary rather than competing. I propose a distinction between intrinsic and extrinsic selection, and the notion of reproductive reach and argue that speciation modes should be discriminated in terms of gene flow, the nature of selection maintaining reproductive reach, and whether the predominant cause is selective or stochastic. I also suggest that the notion of an adaptive “quasispecies” for asexual species is the primitive notion of species, and that members of reproductively coherent sexual species are additionally coadapted to their mating partners. (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 cladistic species concept proposed by Ridley (1989) rests on an undefined notion of speciation and its meaning is thus indeterminate. If the cladistic concept is made determinate through the definition of speciation, then it reduces to a form of whatever species concept is implicit in the definition of speciation and fails to be a truly alternative species concept. The cladistic formalism advocated by Ridley is designed to ensure that species are monophyletic, that they are objectively real entities, and that (...) they are individuals. It is argued that species need not be monophyletic in order to be real entities, and that ancestor-descendant relations are not the only relations that confer individuality on entities. The species problem is recast in terms of a futile quest for a definition of that single kind of entity to which the term species should uniquely apply. (shrink)