According to many philosophical accounts, health is related to the functions and capacities of biological parts. But how do we decide what constitutes the health subject (that is, the bearer of health and disease states) and its biological parts whose functions are relevant for assessing its health? Current science, especially microbiome science, complicating the boundaries between organisms and their environments undermines any straightforward answer. This article explains why this question matters, delineates a few broad options, offers arguments against one option, (...) and draws some modest implications for philosophical accounts of human health. (shrink)

Microbiome research is changing how ecosystems, including animal bodies, are understood. In the case of humans, microbiome knowledge is transforming medical approaches and applications. However, the field is still young, and many conceptual and explanatory issues need resolving. These include how microbiome causality is understood, and how to conceptualize the role microbiomes have in the health status of their hosts and other ecosystems. A key concept that crops up in the medical microbiome literature is “balance.” A balanced microbiome is thought (...) to produce health and an imbalanced one disease. Based on a quantitative and qualitative analysis of how balance is used in the microbiome literature, this “think again” essay critically analyses each of the several subconceptions of balance. As well as identifying problems with these uses, the essay suggests some starting points for filling this conceptual gap in microbiome research. (shrink)

This essay argues for the importance of an organismic perspective in plant biology and considers some of its implications. These include an increased attention to plant-environment interaction and an emphasis on integrated approaches. Furthermore, this essay contextualizes the increased emphasis on the concept of organism in recent years and places the concept in a longer history. Recent developments in biology and worsening environmental crises have led researchers to study plant responses to changing environments with whole plant approaches that situate plants (...) in their environments, emphasizing the intricate and dynamic interaction between them. This renewed attention to the organism recalls the debates of the early twentieth century, when organicism was one of the three main frameworks in biology (along with vitalism and mechanism). Some scholars see this renewed importance today as a “return” of this earlier period. This essay argues that including insights from plant biology will benefit philosophy of biology research that examines the concept of organism and organicism now and in earlier periods. A comprehensive account of the concept of organism should involve a botanical conception of the organism as well as a zoological one (which is more frequently considered). Although this essay does not aim to present a conceptual analysis, it presents examples of how an organismic perspective can be useful for understanding concepts (such as phenotype, stress, etc.) and research processes (such as experiment set-ups, data processes, etc.) in plant biology. Philosophy of biology investigations that aim at a comprehensive understanding of the concept of organism can benefit greatly from examinations of cases in plant biology, both now and in the past. (shrink)

Biological individuality is without a doubt a key concept in philosophy of biology. Questions around the individuality of organisms, species, and biological systems can be traced throughout the philosophy of biology since the discipline’s inception, not to mention the sustained attention they have received in biology and philosophy more broadly. It’s high time the topic got its own Cambridge Element. McConwell’s Biological Individuality falls short of an authoritative overview of the debate on biological individuality. However, it sends a welcome message (...) to new and seasoned scholars to reorient the debate towards practically and politically relevant themes. (shrink)

This paper focuses on physiological integration in multicellular systems, a notion often associated with biological individuality, but which has not received enough attention and needs a thorough theoretical treatment. Broadly speaking, physiological integration consists in how different components come together into a cohesive unit in which they are dependent on one another for their existence and activity. This paper argues that physiological integration can be understood by considering how the components of a biological multicellular system are controlled and coordinated in (...) such a way that their activities can contribute to the maintenance of the system. The main implication of this perspective is that different ways of controlling their parts may give rise to multicellular organizations with different degrees of integration. After defining control, this paper analyses how control is realized in two examples of multicellular systems located at different ends of the spectrum of multicellularity: biofilms and animals. It focuses on differences in control ranges, and it argues that a high degree of integration implies control exerted at both medium and long ranges, and that insofar as biofilms lack long-range control (relative to their size) they can be considered as less integrated than other multicellular systems. It then discusses the implication of this account for the debate on physiological individuality and the idea that degrees of physiological integration imply degrees of individuality. (shrink)

Theoretical accounts of development exhibit several internal tensions and face multiple challenges. They span from the problem of the identification of the temporal boundaries of development (beginning and end) to the characterization of the distinctive type of change involved compared to other biological processes. They include questions such as the role to ascribe to the environment or what types of biological systems can undergo development and whether they should include colonies or even ecosystems. In this chapter we discuss these conceptual (...) issues, and we argue that adopting an organizational approach may help solve or clarify them. -/- While development is usually identified with the achievement of an adult form with the capability to reproduce and therefore maintain a lineage, adopting the organizational approach may provide a different strategy, which focuses also on the maintenance of the current organization of the organism. By doing so an organizational approach favors a switch in perspective which consists in analyzing how organisms maintain their viability at each moment of development rather than considering them as going through intermediate stages of a process directed toward a specific goal state. This developmental dimension of biological organization has yet to be given a general and detailed analysis within the organizational theoretical perspective, apart from some preliminary attempts. How a biological organization is maintained through a series of radical organizational changes and what these changes are issues that still require clarification. In this chapter we offer the beginnings of such an analysis of developmental transitions, understood as changes in functionality brought forth by regulatory mechanisms in the context of the continued maintenance of organizational viability at every step. (shrink)

Phylogenetic models traditionally represent the history of life as having a strictly-branching tree structure. However, it is becoming increasingly clear that the history of life is often not strictly-branching; lateral gene transfer, endosymbiosis, and hybridization, for example, can all produce lateral branching events. There is thus motivation to allow phylogenetic models to have a reticulate structure. One proposal involves the reconciliation of genealogical discordance. Briefly, this method uses patterns of disagreement – discordance – between trees of different genes to add (...) lateral branching events to phylogenetic trees of taxa, and to estimate the most likely cause of these events. I use this practice to argue for: (1) a need for expanded accounts of multiple-models idealization, (2) a distinction between automatic and manual de-idealization, and (3) recognition that idealization may serve the meso-level aims of science in a different way than hitherto acknowledged. (shrink)

This paper introduces the reconstitutor as a comprehensive unit of heredity within the context of evolutionary research. A reconstitutor is the structure resulting from a set of relationships between different elements or processes that are actively involved in the recreation of a specific phenotypic variant in each generation regardless of the biomolecular basis of the elements or whether they stand in a continuous line of ancestry. Firstly, we justify the necessity of introducing the reconstitutor by showing the limitations of other (...) evolutionary conceptions of the unit of heredity, such as the replicator, the reproducer, and the Darwinian individual. We argue that these conceptions are based on the requirement of lineage formation, which we argue to be unnecessary for the existence of evolutionary heredity. In the second part, we introduce the reconstitutor, which we base on the concept of Stability of Traits, and illustrate how it covers cases of hereditary phenomena not covered by the previous accounts. Secondly, we illustrate how the reconstitutor could serve as a platform to rethink ecological inheritance and other forms of inheritance that have been recently introduced under the song/singer model of evolution. (shrink)

This is an article in Thomas J.J. McCloughlin (Ed.) The Nature of Science in Biology: A Resource for Educators. Graphikon Teo, Dublin. -/- Abstract: Philosophers usually tend to think of animals when they think about life, plants often only appear in their works as on the margins, in the background; they are rarely in the centre. However, plant life involves unique processes, including remarkable modes of interaction between plants and their environments. Needless to say, plants are vital parts of ecosystems. (...) Serious attention to plants provides novel and interesting perspectives on many topics in philosophy of biology, including individuality, organisation and disease. Plant biology should have a substantial part in philosophy education. To support this assertion, this paper briefly describes three topics related to plant-environment interaction and explains some of their philosophical implications. These topics are growth, plant hormones and plant-plant microbiota interactions, all of which present crucial aspects related to some prevalent topics in philosophy of biology such as individuality, systems thinking, and holobiont. (shrink)

Microbiome research shows that human health is foundationally intertwined with the ecology of microbial communities living on and in our bodies. This challenges the categorical separation of organisms from environments that has been central to biomedicine, and questions the boundaries between them. Biomedicine is left with an empirical problem: how to understand causal pathways between host health, microbiota and environment? We propose a conceptual tool – environmentality – to think through this problem. Environmentality is the state or quality of being (...) an environment for something else in a particular context: a fully perspectival proposition. Its power lies partly in what Isabelle Stengers has called the efficacy of the word itself, contrasting the dominant sense of the word environment as something both external and fixed. Through three case studies, we argue that environmentality can help think about the causality of microbiota vis-a-vis host health in a processual, relational and situated manner, across scales and temporalities. We situate this intervention within historical trajectories of thought in biomedicine, focusing on the challenge microbiome research poses to an aperspectival body. We argue that addressing entanglements between microbial and human lives requires that the environment is brought into the clinic, thus shortening the conceptual gap between medicine and public health. (shrink)

Both concepts of the holobiont and the immune system are at the heart of an ongoing scientific and philosophical examination concerning questions of the organism’s individuality and identity as well as the relations between organisms and their environment. Examining the holobiont, the question of boundaries and individuality is challenging because it is both an assemblage of organisms with physiological cohesive aspects. I discuss the concept of immunity and the immune system function from the holobiont perspective. Because of the host-microbial close (...) relations of codependence and interdependence, the holobiont is more often than not confused with the host, as the host is the domain in which this entity exists. I discuss the holobiont unique ecological characteristics of microbial assemblages connected to a host in a network of interactions in which the host is one of the organisms in the community but also its landscape. Therefore, I suggest viewing the holobiont as a host-ecosystem and discuss the implication of such a view on the concept of immunity and the meaning of protection. Furthermore, I show that viewing the holobiont as a host ecosystem opens the possibility of using the same ecological definition of boundaries and immunity dealing with an ecological system. Thus, the holobiont’s boundaries and immunity are defined by the persistence of its complex system of interactions integrating existing and new interactions. This way of thinking presents a notion of immunity that materializes as the result of the complex interdependence relations between the different organisms composing the holobiont similar to that of an ecosystem. Taking this view further, I discuss the notion of immunogenicity that is ontologically heterogeneous with various causal explanations of the processes of tolerance and targeted immune response. Finally, I discuss the possible conceptualization of already existing and new biomedical practices. (shrink)

Mammalian placental pregnancy is a neglected problem case for theories of organismality. This example is closer to home than those typically discussed within philosophy of biology. I apply evolutio...

The units or levels of selection debate concerns the question of what kind of biological systems are stable enough that part of their evolution is a result of the process of natural selection acting at their level. Traditionally, the debate has concerned at least two different, though related, questions: the question of the level at which interaction with the environment occurs, and the question of the level at which reproduction occurs. In recent years, biologists and philosophers have discussed a new (...) aspect of this debate, namely the possibility that certain multi-species consortia formed by a host and its microbiome may act as a unit of selection. This thesis, however, has not been without criticism, as it is doubtful that such consortia could meet the conditions required to achieve the degree of stability that would allow them to experience natural selection. The purpose of this paper is to systematically examine such criticisms and to defend the thesis that the holobiont/hologenome can act as a genuine level of selection both in the form of an interactor and in the form of a reproducer. To do so, it will be argued that the microbiome should be characterized in functional rather than taxonomic terms. (shrink)

Both physiological and evolutionary criteria of biological individuality are underpinned by the idea that an individual is a functionally integrated whole. However, a precise account of functional integration has not been provided so far, and current notions are not developed in the details, especially in the case of composite systems. To address this issue, this paper focuses on the organisational dimension of two representative associations of prokaryotes: biofilms and the endosymbiosis between prokaryotes. Some critical voices have been raised against the (...) thesis that biofilms are biological individuals. Nevertheless, it has not been investigated which structural and functional obstacles may prevent them from being fully integrated physiological or evolutionary units. By contrast, the endosymbiotic association of different species of prokaryotes has the potential for achieving a different type of physiological integration based on a common boundary and interlocked functions. This type of association had made it possible, under specific conditions, to evolve endosymbionts into fully integrated organelles. This paper therefore has three aims: first, to analyse the organisational conditions and the physiological mechanisms that enable integration in prokaryotic associations; second, to discuss the organisational differences between biofilms and prokaryotic endosymbiosis and the types of integration they achieve; finally, to provide a more precise account of functional integration based on these case studies. (shrink)

This paper analyzes recent attempts to reject reproduction with lineage formation as a necessary condition for evolution by means of natural selection :560–570, 2008; Stud Hist Philos Sci Part C Stud Hist Philos Biol Biomed Sci 42:106–114, 2011; Bourrat in Biol Philos 29:517–538, 2014; Br J Philos Sci 66:883–903, 2015; Charbonneau in Philos Sci 81:727–740, 2014; Doolittle and Inkpen in Proc Natl Acad Sci 115:4006–4014, 2018). Building on the strengths of these attempts and avoiding their pitfalls, it is argued that (...) a robust formulation of evolution by natural selection without reproduction can be established. The main contribution of this paper is a reformulation of Lewontin’s three principles stating that minimal evolution by natural selection occurs when two conditions are met in a population: fitness-related variation and memory. Paradigmatic evolution by natural selection, which can generate adaptations, takes place when an additional condition is present, namely regeneration. (shrink)

Philosophy of immunology is a subfield of philosophy of biology dealing with ontological and epistemological issues related to the studies of the immune system. While speculative investigations and abstract analyses have always been part of immune theorizing, until recently philosophers have largely ignored immunology. Yet the implications for understanding the philosophical basis of organismal functions framed by immunity offer new perspectives on fundamental questions of biology and medicine. Developed in the context of history of medicine, theoretical biology, and medical anthropology, (...) philosophy of immunology differs from these related branches of study in its focus on traditional philosophical questions concerning identity, individuality, ecology, cognition, scientific methodology and theory construction. This broad agenda derives from immunology’s multifaceted research program that has developed from its initial clinical challenges of host defense, transplantation, autoimmunity, tumor immunology, and allergy. In addition to these well-established research areas, immunity is now understood to play a central role in other physiological functions, development, ecology, and evolutionary mechanics. Holding together these diverse domains of inquiry lie philosophical commitments oriented by organismal identity. In this regard, pertinent issues are raised concerning cognition (organization of immune perception and information processing), the character of individuality (framed by the ecological context of immune-mediated assimilation and rejection), and the dynamics of complex systems (understood as holistic systems biology). Indeed, immunology, in the context of cognitive science, evolutionary biology, environmental sciences, and development provides multi-focal perspectives for philosophy of science. (shrink)

Contemporary biological research has suggested that some host–microbiome multispecies systems (referred to as “holobionts”) can in certain circumstances evolve as unique biological individual, thus being a unit of selection in evolution. If this is so, then it is arguably the case that some biological adaptations have evolved at the level of the multispecies system, what we call hologenomic adaptations. However, no research has yet been devoted to investigating their nature, or how these adaptations can be distinguished from adaptations at the (...) species-level (genomic adaptations). In this paper, we cover this gap by investigating the nature of hologenomic adaptations. By drawing on the case of the evolution of sanguivory diet in vampire bats, we argue that a trait constitutes a hologenomic adaptation when its evolution can only be explained if the holobiont is considered the biological individual that manifests this adaptation, while the bacterial taxa that bear the trait are only opportunistic beneficiaries of it. We then use the philosophical notions of emergence and inter-identity to explain the nature of this form of individuality and argue why it is special of holobionts. Overall, our paper illustrates how the use of philosophical concepts can illuminate scientific discussions, in the trend of what has recently been called metaphysics of biology. (shrink)

A holobiont is a composite organism consisting of a host together with its microbiome, such as a coral with its zooxanthellae. To explain the often intimate integration between hosts and their microbiomes, some investigators contend that selection operates on holobionts as a unit and view the microbiome’s genes as extending the host’s nuclear genome to jointly comprise a hologenome. Because vertical transmission of microbiomes is uncommon, other investigators contend that holobiont selection cannot be effective because a holobiont’s microbiome is an (...) acquired condition rather than an inherited trait. This disagreement invites a simple mathematical model to see how holobiont selection might operate and to assess its plausibility as an evolutionary force. This paper presents two variants of such a model. In one variant, juvenile hosts obtain microbiomes from their parents (vertical transmission). In the other variant, microbiomes of juvenile hosts are assembled from source pools containing the combined microbiomes of all parents (horizontal transmission). According to both variants, holobiont selection indeed causes evolutionary change in holobiont traits. Therefore, holobiont selection is plausibly an effective evolutionary force with either mode of microbiome transmission. The modeling employs two distinct concepts of inheritance, depending on the mode of microbiome transmission: collective inheritance whereby juveniles inherit a sample of the collected genomes from all parents, as contrasted with lineal inheritance whereby juveniles inherit the genomes from only their own parents. A distinction between collective and lineal inheritance also features in theories of multilevel selection. (shrink)

Bourrat and Griffiths :33, 2018) have recently argued that most of the evidence presented by holobiont defenders to support the thesis that holobionts are evolutionary individuals is not to the point and is not even adequate to discriminate multispecies evolutionary individuals from other multispecies assemblages that would not be considered evolutionary individuals by most holobiont defenders. They further argue that an adequate criterion to distinguish the two categories is fitness alignment, presenting the notion of fitness boundedness as a criterion that (...) allows divorcing true multispecies evolutionary individuals from other multispecies assemblages and provides an adequate criterion to single out genuine evolutionary multispecies assemblages. A consequence of their criterion is that holobionts, as conventionally defined by hologenome defenders, are not evolutionary individuals except in very rare cases, and for very specific host-symbiont associations. This paper is a critical response to Bourrat and Griffiths’ arguments and a defence of the arguments presented by holobiont defenders. Drawing upon the case of the hologenomic basis of the evolution of sanguivory in vampire bats, I argue that Bourrat and Griffiths overlook some aspects of the biological nature of the microbiome that justifies the thesis that holobionts are evolutionarily different to other multispecies assemblages. I argue that the hologenome theory of evolution should not define the hologenome as a collection of genomes, but as the sum of the host genome plus some traits of the microbiome which together constitute an evolutionary individual, a conception I refer to as the stability of traits conception of the hologenome. Based on that conception I argue that the evidence presented by holobiont defenders is to the point, and supports the thesis that holobionts are evolutionary individuals. In this sense, the paper offers an account of the holobiont that aims to foster a dialogue between hologenome advocates and hologenome critics. (shrink)

I examine the feminist epistemic values in science, presented by Helen Longino, and their role in framing microbiome causality in the study of inflammatory bowel disease (IBD). In particular, I show how values presented as feminist give an alternative view in scientific theories—focusing on ontological heterogeneity and mutuality of interactions rather than simplicity and one causal direction—when looking at relations between organisms and microorganisms, and between organisms (particularly humans) and their environment. I identify two approaches in microbiome study, an immunological (...) approach that looks at the microbiome pathogenicity and an ecological approach that studies the microbial activity and functions. I show the puzzles stemming from the traditional background beliefs of the immune self and germ theory in the study of IBD causality. Furthermore, I argue for the benefits of a shift to the ecological view of body-microbe interrelations. I conclude with the benefits and advantages of feminist values over traditional ones, both in creating new ways of understanding organisms’ physiology and immune systems and for future biomedical studies involving microbiome causality. (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)

The impressive variation amongst biological individuals generates many complexities in addressing the simple-sounding question what is a biological individual? A distinction between evolutionary and physiological individuals is useful in thinking about biological individuals, as is attention to the kinds of groups, such as superorganisms and species, that have sometimes been thought of as biological individuals. More fully understanding the conceptual space that biological individuals occupy also involves considering a range of other concepts, such as life, reproduction, and agency. There has (...) been a focus in some recent discussions by both philosophers and biologists on how evolutionary individuals are created and regulated, as well as continuing work on the evolution of individuality. (shrink)

The theory of evolution by natural selection is, perhaps, the crowning intellectual achievement of the biological sciences. There is, however, considerable debate about which entity or entities are selected and what it is that fits them for that role. This article aims to clarify what is at issue in these debates by identifying four distinct, though often confused, concerns and then identifying how the debates on what constitute the units of selection depend to a significant degree on which of these (...) four questions a thinker regards as central. (shrink)

This paper addresses the topic of determinism in contemporary microbiome research. I distinguish two types of deterministic claims about the microbiome, and I show evidence that both types of claims are present in the contemporary literature. First, the idea that the host genetics determines the composition of the microbiome which I call “host-microbiome determinism”. Second, the idea that the genetics of the holobiont (the individual unit composed by a host plus its microbiome) determines the expression of certain phenotypic traits, which (...) I call “microbiome-phenotype determinism”. Drawing on the stability of traits conception of individuality (Suárez in Hist Philos Life Sci 42:11, 2020) I argue that none of these deterministic hypotheses is grounded on our current knowledge of how the holobiont is transgenerationally assembled, nor how it expresses its phenotypic traits. (shrink)

Since the last decades of the twentieth and the beginning of the twenty-first century, the use of metaphysics by philosophers when approaching conceptual problems in biology has increased. Some philosophers call this tendency in philosophy of biology ‘Metaphysics of Biology’. In this paper, I aim at characterizing Metaphysics of Biology by paying attention to the diverse ways philosophers use metaphysics when addressing conceptual problems in biology. I will claim that there are two different modes of doing Metaphysics of Biology, namely (...) Metaphysics for Biology and Metaphysics in Biology. (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 article proposes two conditions to assess whether an entity at a level of description is a unit of selection qua interactor. These two conditions make it possible to (1) distinguish biologically relevant entities from arbitrary ones and (2) distinguish units that can _potentially_ enter a selection process from those that have already done so. I show that the classical approaches used in the literature on units and levels of selection do not fare well with respect to either or both (...) of these desiderata. (shrink)

One Health medicine aims to improve health by focusing on the relations between the health of humans, animals, and the environment. However, One Health does not provide a clear idea of these relations, which are still represented as conceptually separated and not as one health, as the name implies. Inspired by holobiont research, I suggest a new model and conceptual framework for One Health that expands the notion of the biological patient by providing a gradational and dynamic understanding of environments, (...) patients, and their relations. This new model conceptualizes humans and non-humans, individual organisms, and collectives, as belonging to one system that allows for more or less inclusive understandings of patients. As such, it resolves the conceptual tensions of different One Health approaches and supports the implementation of One Health as an interdisciplinary research field. (shrink)

Taking the case of H. pylori and ulcer, Lynch et al., demonstrate how framing Koch’s postulate by an interventionist account clarifies the latter’s explanatory strength in proportionality with the weaknesses in specificity and stability due to the influence of background conditions. They suggest this approach as an efficient way to bypass the enigma of background conditions and microbial activity in the microbiome’s causal relations. However, it is the background conditions and the microbial interactions in the stomach that determine whether the (...) presence of H. pylori results in an ulcer. I agree with their analysis of the problems and challenges with the microbiome causal explanation but argue that their suggested framework is insufficient without a proper understanding and inclusion of the background conditions and microbial interactions. The reductionist approach fits well within the model of causal explanation that centers on one causal entity. However, such a model is weak in specificity and is too broad because it does not address the factors of microbial activity and background conditions. I argue that for a better causal explanation with explanatory strength in specificity, it is essential to include the background conditions and microbial interactions. Furthermore, I argue that this inclusion changes the framework of the causal relations from looking for the causal entity to looking at the causal process. (shrink)

Individuality is an important concept in biology, yet there are many non-equivalent criteria of individuality expressed in different kinds of biological individuals. This article evaluates these different kinds in terms of their capacity to support explanatory generalizations over the systems they individuate. Viewing the problem of individuality from this perspective promotes a splitting strategy in which different kinds make different epistemic trade-offs that suit them for different explanatory roles. I argue that evolutionary individuals, interpreted as forming a functional kind, face (...) difficulties of individuation and explanatory power that are mitigated by relying on more structurally based properties and non-evolutionary kinds. 1Introduction2Kinds of Biological Individuals3Evolutionary Individuals and Functional Kinds4Evolutionary versus Non-evolutionary Kinds of Individuals 4.1Physiological individuality4.2Ecological individuality4.3Developmental individuality5Conclusion. (shrink)

Recent attention to complex group-level behavior amongst bacteria has led some to conceive of multicellular clusters of bacteria as individuals. In this article, I assess these recent claims by first drawing a distinction between two concepts of individuality: physiological and evolutionary. I then survey cases that are representative of three different modes of growth: myxobacteria (surface-attached agglomerative growth), Bacillus subtilis (agglomerative growth not attached to a surface), and cyanobacteria (filamentous growth). A closer look at these cases indicates that multicellular individuality (...) among bacteria is remarkably complex. Physiologically, the three cases of multicellular clusters do not form physiological individuals. But matters are different when it comes to evolutionary individuality; although multicellular clusters that grow by agglomeration are not highly individuated, filament-forming groups achieve a relatively high degree of individuality. I also suggest that debates about bacterial multicellular individuality may have been obscured by a failure to see that selection on highly individuated groups is by no means the only mechanism to bring about the complex group-level behaviors that have led some to view bacteria as multicellular individuals. (shrink)

We assess the arguments for recognising functionally integrated multispecies consortia as genuine biological individuals, including cases of so-called ‘holobionts’. We provide two examples in which the same core biochemical processes that sustain life are distributed across a consortium of individuals of different species. Although the same chemistry features in both examples, proponents of the holobiont as unit of evolution would recognize one of the two cases as a multispecies individual whilst they would consider the other as a compelling case of (...) ecological dependence between separate individuals. Some widely used arguments in support of the ‘holobiont’ concept apply equally to both cases, suggesting that those arguments have misidentified what is at stake when seeking to identify a new level of biological individuality. One important aspect of biological individuality is evolutionary individuality. In line with other work on the evolution of individuality, we show that our cases can be distinguished by focusing on the fitness alignment between the partners of the consortia. We conclude that much of the evidence currently presented for the ubiquity and importance of multi-species individuals is simply not to the point, at least unless the issue of biological individuality is firmly divorced from the question of evolutionary individuality. (shrink)

If ecological systems are functionally organised, they can possess functions or malfunctions. Natural function would provide justification for conservationists to act for the protection of current ecological arrangements and control the presence of populations that create ecosystem malfunctions. Invasive species are often thought to be malfunctional for ecosystems, so functional arrangement would provide an objective reason for their control. Unfortunately for this prospect, I argue no theory of function, which can support such normative conclusions, can be applied to large scale (...) ecosystems. Instead ecological systems have causal structure, with small clusters of populations achieving functional arrangement. This, however, does not leave us without reason to control invasive species. We can look at the causal arrangement of ecological systems for populations that support ecological features that we should preserve. Populations that play a causal role in reducing biodiversity should be controlled, because biodiversity is a good all prudent agents should want to preserve. (shrink)

On the basis of findings from developmental biology, some researchers have argued that evolutionary theory needs to be significantly updated. Advocates of such a “developmental update” have, among other things, suggested that we need to re-conceptualize units of selection, that we should expand our view of inheritance to include environmental as well as genetic and epigenetic factors, that we should think of organisms and their environment as involved in reciprocal causation, and that we should reevaluate the rates of evolutionary change. (...) However, many of these same conclusions could be reached on the basis of other evidence, namely from microbiology. In this paper, I ask why microbiological evidence has not had a similarly large influence on calls to update biological theory, and argue that there is no principled reason to focus on developmental as opposed to microbiological evidence in support of these revisions to evolutionary theory. I suggest that the focus on developmental biology is more likely attributable to historical accident. I will also discuss some possible room for overlap between developmental and microbiology, despite the historical separation of these two subdisciplines. (shrink)

Mammals are usually considered unproblematic as biological individuals. This article contends the opposite. Once we consider pregnancy, criteria for biological individuality are not easily applicab...

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)

. Early microbiome research found numerous associations between microbial community patterns and host physiological states. These findings hinted at community-level explanations. “Top-down” experiments, working with whole communities, strengthened these explanatory expectations. Now, “bottom-up” mechanism-seeking approaches are dissecting communities to focus on specific microbes carrying out particular biochemical activities. To understand the interplay between methodological and explanatory scales, we examine claims of “dysbiosis,” when host illness is proposed as the consequence of a community state. Our analysis concludes with general observations about (...) how methodologies relate to explanations, and the implications for microbiome research. (shrink)

Lynch et al., in an article in this issue, argue that an entire microbiome is rarely, if ever, the right target of analysis for causal explanations in microbiome research. They argue, using interventionist criteria of proportionality, specificity and stability, for restricting causal claims to the smallest subset of microbes—a causal core—that generate the effect of interest. A further question remains: what kind of interactions generate a consortium of microbes that can operate as causal agents in this manner? Here I introduce (...) two possible kinds of such consortia: ‘trojan horses’ and ‘syntrophic’ individuals. (shrink)

Debates concerning the units and levels of selection have persisted for over fifty years. One major question in this literature is whether units and levels of selection are genuine, in the sense that they are objective features of the world, or merely reflect the interests and goals of an observer. Scientists and philosophers have proposed a range of answers to this question. This Element introduces this literature and proposes a novel contribution. It defends a realist stance and offers a way (...) of delineating genuine levels of selection by invoking the notion of a functional unit. (shrink)

This article defends a selective eliminativist position with respect to the concept of “biological lineage” as used in certain areas of contemporary evolutionary biology. We argue that its primary epistemic roles in these contexts—explaining social evolution and cumulative selection—clash with empirical evidence, and that enforcing the concept of “lineage” even obstructs fruitful research avenues in several biological research fields, including phylogenetic research. Drawing on this, we suggest that, in many instances, it would be best to get rid of the concept (...) of “lineage” and think in terms that are more closely aligned with the empirical complexity of the biological world. Specifically, this entails that, instead of looking for the lineage that may have given rise to the entities possessing certain biological characteristics, biologists should generally look for any potential process allowing such possession, with the formation of a lineage just one possibility among many. (shrink)

Abstract‘Obesity’ has, for decades, been a subject of intense scientific and public interest, and remains a key target for postgenomic science. I examine the emergence of determinism in research into ‘obesity’ in the postgenomic field of metabolomics. I argue that determinism appears in metabolomics research in two ways: firstly, fragmentation and narrow construal of the environment is evident in metabolomics studies on weight loss interventions, resulting in particular features of the environment (notably, dietary intake) having outsized influence while the wider (...) social environment is neglected. Secondly, studies aiming to characterize the metabolic signature of ‘obesity’ are guided by a commitment to a deterministic connection between ‘obesity’ and dysfunction, leading to a neglect or distortion of metabolic heterogeneity across individuals regardless of body size. (shrink)

It is becoming increasingly clear that most, if not all, animals and plants are associated with a diverse array of resident gut microbiota. This symbiosis is regulated by host-microbiome interactions which influence the development, homeostasis, adaptation and evolution of the host. Recent evidence indicated that these interactions can also affect the host germline and have a potential of supporting transgenerational effects, including inheritance of acquired characteristics. Taken together, the influence of gut bacteria on the host soma and germline could potentially (...) give rise to emergent phenotypes, which may be partially inherited by three distinguishable modes of transgenerational influence of gut bacteria: 1) “soma-to-soma” 2) “soma-to-germline” and 3) “soma-germline-soma”. Here, we discuss these possibilities in light of evidence supporting bacterial-mediated modes of transgenerational inheritance. All animals are consortiums of hosts and microbiota. Their interactions influence many aspects of the adaptation and evolution of the Holobiont. The host germline can also be affected which can give rise to new modes of transgenerational influence of gut bacteria: 1) “soma-to-soma” 2) “soma-to-germline,” and 3) “soma-germline-soma.”. (shrink)