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)

The hologenome concept of evolution is a hypothesis about the evolution of animals and plants. It asserts that the evolution of animals and plants was partially triggered by their interactions with their symbiotic microbiomes. In that vein, the hologenome concept posits that the holobiont (animal host + symbionts of the microbiome) is a unit of selection. -/- The hologenome concept has been severely criticized on the basis that selection on holobionts would only be possible if there were a tight transgenerational (...) host-genotype-to-symbiont-genotype connection. As our current evidence suggests that this is not the case for most of the symbiont species that compose the microbiome of animals and plants, the opportunity for holobiont selection is very low in relation to the opportunity for selection on each of the species that compose the host microbiome. Therefore, holobiont selection will always be disrupted ‘from below’, by selection on each of the species that compose the microbiome. -/- This thesis constitutes a conceptual effort to defend philosophically the hologenome concept. I argue that the criticism according to which holobiont selection requires tight transgenerational host-genotype-to-symbiont-genotype connection is grounded on a metaphysical view of the world according to which the biological hierarchy needs to be nested, such that each new level of selection includes every entity from below. Applied to hologenomes, it entails that the hologenome is a collection of genomes, and selection of hologenomes is assumed to entail cospeciation of the host with the species that constitute its microbiome. -/- Against that interpretation, I propose the ‘stability of traits’ account, according to which hologenome evolution is the result of the action of natural selection in a non-nested hierarchical world. In that vein, hologenome evolution does not entail cospeciation, and thus it does not require tight transgenerational host-genotype-to-symbiont-genotype connection. By embracing a multilevel selection perspective, I argue that hologenome evolution results from the simultaneous action of natural selection on each of the lineages that compose the microbiome, and on the assemblage composed by the host genome plus the functional traits of its microbiome. Hologenome selection occurs when the evolution of the traits of the microbiome result from their effects on the fitness of the host, and it can take the form of multilevel selection 1, or multilevel selection 2. In both cases, hologenome selection entails the evolution of microbiome traits, as well as evolution of the host genome, rather than cospeciation of lineages. (shrink)

Racial constructionists, anti-naturalists, and anti-realists have challenged users of the biological race concept to provide and defend, from the perspective of biology, biological philosophy, and ethics, a biologically informed concept of race. In this paper, an ontoepistemology of biology is developed. What it is, by this, to be "biological real" and "biologically meaningful" and to represent a "biological natural division" is explained. Early 18th century race concepts are discussed in detail and are shown to be both sensible and not greatly (...) dissimilar to modern concepts. A general biological race concept (GBRC) is developed. It is explained what the GBRC does and does not entail and how this concept unifies the plethora of specific ones, past and present. Other race concepts as developed in the philosophical literature are discussed in relation to the GBRC. The sense in which races are both real and natural is explained. Racial essentialism of the relational sort is shown to be coherent. Next, the GBRC is discussed in relation to anthropological discourse. Traditional human racial classifications are defended from common criticisms: historical incoherence, arbitrariness, cluster discordance, etc. Whether or not these traditional human races could qualify as taxa subspecies – or even species – is considered. It is argued that they could qualify as taxa subspecies by liberal readings of conventional standards. Further, it is pointed out that some species concepts potentially allow certain human populations to be designated as species. It is explained why, by conventional population genetic and statistical standards, genetic differences between major human racial groups are at least moderate. Behavioral genetic differences associated with human races are discussed in general and in specific. The matter of race differences in cognitive ability is briefly considered. Finally, the race concept is defended from various criticisms. First, logical and empirical critiques are dissected. These include: biological scientific, sociological, ontological, onto-epistemological, semantic, and teleological arguments. None are found to have any merit. Second, moral-based arguments are investigated in context to a general ethical frame and are counter-critiqued. Racial inequality, racial nepotism, and the “Racial Worldview" are discussed. What is dubbed the Anti-Racial Worldview is rejected on both empirical and moral grounds. Finally, an area of future investigation – the politics of the destruction of the race concept – is pointed to. (shrink)

The genealogy-based classificatory programs of Kant and Darwin are briefly discussed for context. It is detailed how in biology there is no unambiguous term to reference infraspecific-level descent-based divisions. The term lineage population is introduced and defined for analytic purposes as one of a set of inter-fertile divisions of organisms into which members are arranged by propinquity of descent. It is argued that the lineage population concept avoids the ambiguities associated with related biological and anthropological concepts and polysemes such as (...) population, ethnicity, and race. Other terms and concepts, such as form, cline, cluster, geographic population, breeding population, genetic population, breed, species, subspecies, ancestry, geographic ancestry, biogeographic ancestry, ancestral population, ancestry population, natural division, and population lineage, are discussed in relation to this concept. It is concluded that the lineage population concept is a useful analytic tool which describes, in line with the Kantian/Darwinian perspective, an interesting class of biological variation. (shrink)

Biodiversity is a key concept in the biological sciences. While it has its origin in conservation biology, it has become useful across multiple biological disciplines as a means to describe biological variation. It remains, however, unclear what particular biological units the concept refers to. There are currently multiple accounts of which biological features constitute biodiversity and how these are to be measured. In this paper, I draw from the species concept debate to argue for a set of desiderata for the (...) concept of “biodiversity” that is both principled and coheres with the concept’s use. Given these desiderata, this concept should be understood as referring to difference quantified in terms of the phylogenetic structure of lineages, also known as the ‘tree of life’. (shrink)

-/- Because species names play an important role in scientific communication, it is more important that species be understood to be taxa than that they be equated with functional ecological or evolutionary entities. Although most biologists would agree that taxa are composed of organisms that share a unique common history, 2 major challenges remain in developing a species-as-taxa concept. First, grouping: in the face of genealogical discordance at all levels in the taxonomic hierarchy, how can we understand the nature of (...) taxa? Second, ranking: what criteria should be used to designate certain taxa in a nested series as being species? The grouping problem can be solved by viewing taxa as exclusive groups of organisms— sets of organisms that form a clade for a plurality of the genome (more than any conflicting set). However, no single objective criterion of species rank can be proposed. Instead, the species rank should be assigned by practitioners based on the semisubjective application of a set of species-ranking criteria. Although these criteria can be designed to yield species taxa that approximately match the ecological, evolutionary, and morphological entities that taxonomists have traditionally associated with the species rank, such a correspondence cannot be enforced without undermining the assumption that species are taxa. The challenge and art of monography is to use genealogical and other kinds of data to assign all organisms to one and only one species-ranked taxon. Various implications of the species-as-ranked-taxa view are discussed, including the synchronic nature of taxa, fossil species, the treatment of hybrids, and species nomenclature. I conclude that, although challenges remain, adopting the view that species are ranked taxa will facilitate a much-needed revolution in taxonomy that will allow it to better serve the biodiversity informatic needs of the 21st century. (shrink)

For more than fifty years, taxonomists have proposed numerous alternative definitions of species while they searched for a unique, comprehensive, and persuasive definition. This monograph shows that these efforts have been unnecessary, and indeed have provably been a pursuit of a will o’ the wisp because they have failed to recognize the theoretical impossibility of what they seek to accomplish. A clear and rigorous understanding of the logic underlying species definition leads both to a recognition of the inescapable ambiguity that (...) affects the definition of species, and to a framework-relative approach to species definition that is logically compelling, i.e., cannot not be accepted without inconsistency. An appendix reflects upon the conclusions reached, applying them in an intellectually whimsical taxonomic thought experiment that conjectures the possibility of an emerging new human species. (shrink)

This paper examines the species problem in microbiology and its implications for the species problem more generally. Given the different meanings of ‘species’ in microbiology, the use of ‘species’ in biology is more multifarious and problematic than commonly recognized. So much so, that recent work in microbial systematics casts doubt on the existence of a prokaryote species category in nature. It also casts doubt on the existence of a general species category for all of life (one that includes both prokaryotes (...) and eukaryotes). Prokaryote biology also undermines recent attempts to save the species category, such as the suggestion that species are metapopulation lineages and the idea that ‘species’ is a family resemblance concept. (shrink)

Biologists and philosophers that debate the existence of the species category fall into two camps. Some believe that the species category does not exist and the term 'species' should be eliminated from biology. Others believe that with new biological insights or the application of philosophical ideas, we can be confident that the species category exists. This paper offers a different approach to the species problem. We should be skeptical of the species category, but not skeptical of the existence of those (...) taxa biologists call 'species.' And despite skepticism over the species category, there are pragmatic reasons for keeping the word 'species.' This approach to the species problem is not new. Darwin employed a similar strategy to the species problem 150 years ago. (shrink)

There is an interesting parallel between two debates in different domains of contemporary analytic philosophy. One is the endurantism– perdurantism, or three-dimensionalism vs. four-dimensionalism, debate in analytic metaphysics. The other is the debate on the species problem in philosophy of biology. In this paper I attempt to cross-fertilize these debates with the aim of exploiting some of the potential that the two debates have to advance each other. I address two issues. First, I explore what the case of species implies (...) regarding the feasibility of particular positions in the endurantism– perdurantism debate. I argue that the case of species casts doubt on the recent claim that three-dimensionalism and four-dimensionalism are equivalent descriptions of the same underlying reality. Second, and conversely, I examine whether the metaphysical worry about three-dimensionalism and four-dimensionalism can help us to better understand the nature of biological species. I show that analyzing the thesis that species are individuals against the background of the endurantism– perdurantism debate allows us to explicate two different ways in which this thesis can be interpreted. (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)

After having reconstructed a minimal biological characterisation of species, we endorse an “empirical approach” based on the idea that it is the peculiar evolutionary history of the species at issue—its peculiar origination process, its peculiar metapopulation structure and the peculiar mixture and strength of homeostatic processes vis à vis heterostatic ones—that determines species’ identity at a time and through time. We then explore the consequences of the acceptance of the empirical approach in settling the individuals versus kinds dispute. In particular, (...) while conceptual arguments have been proposed to show that species can be equally treated as individuals and kinds because mereology’s and set-theory’s languages are inter-translatable, we advance instead a causal argument to sustain the claim that each species is both a kind and an individual. (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)

Historians tend to speak of the problem of the origin of species or the species question, as if it were a monolithic problem. In reality, the phrase refers to a, historically, surprisingly fluid and pluriform scientific issue. It has, in the course of the past five centuries, been used in no less than ten different ways or contexts. A clear taxonomy of these separate problems is useful or relevant in two ways. It certainly helps to disentangle confusions that have inevitably (...) emerged in the literature in its absence. It may, secondly, also help us to gain a more thorough understanding, or sharper view, of the history of evolutionary thought. A consequent problem-centric look at that history through the lens of various origin of species problems certainly yields intriguing results, including and particularly for our understanding of the genesis of the Wallace–Darwin theory of evolution through natural selection. (shrink)