Some philosophers of biology state that the metaphysical status of biological species is context determined by the use different branches of biology make of their corresponding proper names, so that one and the same biological species can be both an individual and a natural kind. In this paper, I aim to undermine the idea, often associated with the present thesis, according to which the debate about the metaphysical status of biological species should be deflated, since it would be possible to (...) translate every sentence from natural-kind talk to individual-talk and vice versa. I offer a charitable interpretation of the principle grounding such an idea and show how it is in tension with independent theoretical biological notions. (shrink)

Biological individuality is a major topic of discussion in biology and philosophy of biology. Recently, several objections have been raised against traditional accounts of biological individuality, including the objections of monism, theory-centrism, ahistoricity, disciplinary isolationism, and the multiplication of conceptual uncertainties. In this introduction, I will examine the current philosophical landscape about biological individuality, and show how the contributions gathered in this special issue address these five objections. Overall, the aim of this issue is to offer a more diverse, unifying, (...) and scientifically informed conception of what a biological individual is. (shrink)

This paper argues that a plant together with the symbiotic fungus attached to its roots, a mycorrhizal collective, is an evolutionary individual, and further, that mycorrhizal individuality has important implications for evolutionary theory. Theoretical individuation is defended and then employed to show that mycorrhizal collectives function as interactors according to David Hull’s replicator-interactor model of evolution by natural selection, and because they have the potential to engage in pseudo-vertical transmission, mycorrhizal collectives also function as Darwinian individuals, according to Peter Godfrey-Smith’s (...) Darwinian Populations model of evolution by natural selection. Mycorrhizae in nature usually connect the roots of multiple plants, so mycorrhizal individuality entails the existence of overlapping evolutionary individuals, and because the potential to engage in pseudo-vertical transmission comes in degrees, it follows that these overlapping evolutionary individuals also come in degrees. I suggest here that the degree of evolutionary individuality in a symbiotic collective corresponds to its probability of reproducing with vertical or pseudo-vertical transmission. This probability constitutes a fourth parameter of graded Darwinian individuality in collective reproducers and warrants an update to Godfrey-Smith’s 3D model. (shrink)

Philosophers are approaching a consensus that biological individuality, including evolutionary individuality, comes in degrees. Graded evolutionary individuality presents a puzzle when juxtaposed with another widely embraced view: that evolutionary individuality follows from being a selectable member of a Darwinian population. Population membership is, on the orthodox view, a bivalent condition, so how can members of Darwinian populations vary in their degree of individuality? This article offers a solution to the puzzle, by locating difference in degree of evolutionary individuality at the (...) level of population lineages, some of which are more Darwinian than others. In doing so, it sheds light on graded individuality in overlapping and nested population lineages, such as those that arise in multilevel selection and symbiotic collectives. (shrink)

Biological lineages move through time, space, and each other. As they do, they diversify, diverge, and grade away from and into one another. One result of this is genealogical discordance; i.e., the lineages of a biological entity may have different histories. We see this on numerous levels, from microbial networks, to holobionts, to population-level lineages. This paper considers how genealogical discordance impacts our study of species. More specifically, I consider this in the context of three framing questions: (1) How, if (...) at all, does genealogical discordance challenge, modify, or revise how we conceive of species? (2) How has growing appreciation of genealogical discordance impacted scientific practice? Of systematics in particular? (3) How do lineages at different levels diverge and diversify? All told, genealogical discordance enriches and complicates our taxonomic ontology, as well as the practice of reconstructing phylogenies. This presents both challenges and opportunities for the study of divergence and diversification. (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)