I defend a radical interpretation of biological populations—what I call population pluralism—which holds that there are many ways that a particular grouping of individuals can be related such that the grouping satisfies the conditions necessary for those individuals to evolve together. More constraining accounts of biological populations face empirical counter-examples and conceptual difficulties. One of the most intuitive and frequently employed conditions, causal connectivity—itself beset with numerous difficulties—is best construed by considering the relevant causal relations as ‘thick’ causal concepts. I (...) argue that the fine-grained causal relations that could constitute membership in a biological population are huge in number and many are manifested by degree, and thus we can construe population membership as being defined by massively multidimensional constructs, the differences between which are largely arbitrary. I end by showing that positions in two recent debates in theoretical biology depend on a view of biological populations at odds with the pluralism defended here. (shrink)

Essentialism is widely regarded as a mistaken view of biological kinds, such as species. After recounting why (sections 2-3), we provide a brief survey of the chief responses to the “death of essentialism” in the philosophy of biology (section 4). We then develop one of these responses, the claim that biological kinds are homeostatic property clusters (sections 5-6) illustrating this view with several novel examples (section 7). Although this view was first expressed 20 years ago, and has received recent discussion (...) and critique, it remains underdeveloped and is often misrepresented by its critics (section 8). (shrink)

After decades of debates about species concepts, there is broad agreement that species are evolving lineages. However, species classification is still in a state of disorder: different methods of delimitation lead to competing outcomes for the same organisms, and the groups recognised as species are of widely different kinds. This paper considers whether this problem can be resolved by developing a unitary scale for evolutionary independence. Such a scale would show clearly when groups are comparable and allow taxonomists to choose (...) a conventional threshold of independence for species status. Existing measurement approaches to species delimitation are typically shot down by what I call the heterogeneity objection, according to which independently evolving groups are too heterogeneous to be captured by a single scale. I draw a parallel with the measurement of temperature to argue that this objection does not provide sufficient reasons to abandon the measurement approach, and that such an approach may even help to make the vague notion of evolutionary independence more precise. (shrink)

I defend a radical interpretation of biological populations—what I call population pluralism—which holds that there are many ways that a particular grouping of individuals can be related such that the grouping satisfies the conditions necessary for those individuals to evolve together. More constraining accounts of biological populations face empirical counter-examples and conceptual difficulties. One of the most intuitive and frequently employed conditions, causal connectivity—itself beset with numerous difficulties—is best construed by considering the relevant causal relations as ‘thick’ causal concepts. I (...) argue that the fine-grained causal relations that could constitute membership in a biological population are huge in number and many are manifested by degree, and thus we can construe population membership as being defined by massively multidimensional constructs, the differences between which are largely arbitrary. I end by showing that positions in two recent debates in theoretical biology depend on a view of biological populations at odds with the pluralism defended here. 1 Introduction2 Biological Population, Broad and Narrow3 Difficulties with Narrow Biological Population Conditions3.1 Against the genealogical condition3.2 Against the conspecificity condition3.3 Against the proximity condition3.4 Against the typology condition4 Causal Connectivity5 Massively Multidimensional Population Constructs6 Population Uniqueness and Natural Selection6.1 Statisticalism and its discontents6.2 Price at what price?7 Conclusion. (shrink)

We argue for a new conventionalism about many kinds of evolutionary groups, including clades, cohesive units, and populations. This rejects a consensus, which says that given any one of the many legitimate grouping concepts, only objective biological facts determine whether a collection is such a group. Surprisingly, being any one kind of evolutionary group typically depends on which of many incompatible values are taken by suppressed variables. This is a novel pluralism underlying most any one group concept, rather than a (...) familiar pluralism claiming many concepts are legitimate. Consequently, we must help biological facts determine grouphood, even when given a single grouping concept. (shrink)

There is growing agreement among taxonomists that species are independently evolving lineages. The central notion of this conception, evolutionary independence, is commonly operationalized by taxonomists in multiple, diverging ways. This leads to a problem of operationalization-dependency in species classification, as species delimitation is not only dependent on the properties of the investigated groups, but also on how taxonomists choose to operationalize evolutionary independence. The question then is how the operationalization-dependency of species delimitation is compatible with its objectivity and reliability. In (...) response to this problem, various taxonomists have proposed to integrate multiple operationalizations of evolutionary independence for delimiting species. This paper first distinguishes between a standard and a sophisticated integrative approach to taxonomy, and argues that it is unclear how either of these can support the reliability and objectivity of species delimitation. It then draws a parallel between the measurement of physical quantities and species delimitation to argue that species delimitation can be considered objective and reliable if we understand the sophisticated integrative approach as assessing the coherence between the idealized models of multiple operationalizations of evolutionary independence. (shrink)

According to the species-as-individuals thesis(hereafter S-A-I), species are cohesive entities. Barker and Wilson recently pointed out that the type of cohesion exhibited by species is fundamentally different from that of organisms (paradigmatic individuals), suggesting that species are homeostatic property cluster kinds. In this article, I propose a shift in how to approach cohesion in the context of S-A-I: instead of analyzing the different types of cohesion and questioning whether species have them, I focus on the role played by cohesion in (...) the identity of individuals. This shift allows us to recognize why cohesion matters to S-A-I, as well as to reconceive the analogy between species and organisms (paradigmatic individuals), and also allows us to highlight the context sensitivity of both ‘‘cohesion’’ and ‘‘individuals.’’ From this perspective, I identify two problems in Barker and Wilson’s argumentation. Firstly, the authors fail to recognize that species are individuals even if they do not have the same type of cohesion that organisms have. Secondly, their argument relies on a misinterpretation of S-A-I. I conclude that species cohesion is still best framed as a feature of species individuality rather than a feature of species as homeostatic property cluster kinds. The arguments presented here contribute to the re-articulation and reevaluation of S-A-I in the face of contemporary discussions. (shrink)

Evolutionary conceptions of species place special weight on each species having dynamic independence as a unit of evolution. However, the idea that species have their own historical fates, tendencies, or roles has resisted systematic analysis. Growing evidence from population genomics shows that many paradigm species regularly engage in hybridization. How can species be defined in terms of independent evolutionary identities if their genomes are dynamically coupled through lateral exchange? I introduce the concept of a “composite lineage” to distinguish species and (...) subspecies on the basis of the proportion of a group’s heritable traits that are uncoupled from reproductive exchange. (shrink)