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)

Die von der Beobachtung des menschlichen Auges unabhängigen genetischen Relationen zwischen den Individuen sind für die Begründung des Artbegriffs das Wesentliche. Die Tatsache, dass die Systematiker in der Praxis meist rein morphologisch arbeiten und nur in wenigen Ausnahmefällen das Verhalten der Individuen einander gegenüber direkt studieren, ändert daran durchaus nichts.Es gibt zwei grundverschiedene Weisen die Individuen und deren genetische Relationen zu betrachten. Entweder man schaut “horizontal”, d.h. innerhalb einer kurzen Zeitspanne, oder man übersieht das Ganze “vertikal”, d.h. ohne zeitliche Begrenzung.Anhand (...) einer Kombination von Abstammungslehre und Ergebnissen der Genetik wirde in Modell formiert, an dem die mögliche Modell-Objektivität von bestimmten Gruppierungen von Individuen zu Arten abgemessen wird.Bei der horizontalen Betrachtungsweise gibt es modell-objektive Arten nach der DefinitionMayr's : “Species are groups of actually or potentially interbreeding natural populations, which are isolated from other such groups”. Gruppe A ist so innerhalb der arbiträr begrenzten Periode p eine modell-objektive Art in der Relation zu Gruppe B.Vertikal sind keine modell-objektiven Gruppierungen von Individuen möglich. So müssen Arten einander gegenüber arbiträr abgegrenzt werden.Eine horizontale Art kann manchmal arbiträr in trinominal benannte Unterarten aufgeteilt werden, auf Grund von geographisch lokalisierten morphologischen Merkmalen. Eine analoge trinominale Benennung von stratigraphischen Rassen oder vertikalen Unterarten, nach zeitlich lokalisierten Merkmalen, ist sehr verwirrend. Es gibt keinen einzigen zwingenden Grund vertikal neben Arten, als eine spezielle Kategorie, auch noch Unterarten zu konstruieren. (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)

I begin with a description of the benefits and limits of DNA barcoding as presented by its advocates not its critics. Next, I argue that due to the mutually dependent relationship between defining and delimiting species, all systems of classification are grounded in theory, even if only implicitly. I then proceed to evaluate DNA barcoding in that context. In particular, I focus on the barcoders’ use of a sharp boundary by which to delimit species, arguing that this boundary brings along (...) additional theoretical commitments inconsistent with the way taxonomists conceive of species, viz., as entities that have vague boundaries and that cannot be defined by any single attribute other than ancestry. Given these inconsistencies, I conclude that even if groupings based on DNA barcodes match those of an existing taxonomy, the two systems of classification are not necessarily tracking the same entities, i.e., species. (shrink)

This essay supposes that the question of what treatment of animals is morally acceptable cannot be decided in any straightforward way by appeals to 'equal consideration of interests' or to animal rights. Instead it seeks to survey a variety of proposals as to how we ought to adjudicate interspecific conflicts of interests - proposals that are both 'speciesist' and 'non-speciesist' in nature. In the end one proposal is defended as the most reasonable one, and is claimed to provide a partial (...) basis for developing an adequate theory of interspecific justice. In the course of this argument the challenge posed by radical critics of current treatment of animals (e.g. Tom Regan and Peter Singer) is considered. The schema of a theory developed here partly supports and partly conflicts with positions they have defended. Regarding the latter point it proposes a non-anthropocentric basis for discounting the interests of sentient animals. (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)

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)