The dual role of microbial communities as either beneficial/functional or harmful/pathogenic involves two issues concerning causality in physiology and medicine, etiology of disease, and the notion of function in biology. Causal explanation formulated by the germ theory of disease and the Koch postulates connects the existence of a specifically identified microbe to disease by the isolation and identification of a pathogen from an organism with the disease and the successful infection of a healthy individual. Similarly, microbiome research in medicine centers (...) on taxonomic composition in correlation with physiological conditions and germ-free mice experimentations to establish causal connections. However, because the microbiome is an ecological community, it lacks the specificity of identification assumed in the germ theory. Furthermore, the ecological aspects within and between microbiomes such as background conditions, microbial interactions, and interdependence, are treated as confounding. Looking at ecological studies, the causal explanations are less specific regarding complex systems with their processes of interactions. This article makes the following two points: One is that microbiome causality in the host should be understood similarly to the microbiome causality in an ecosystem. The second is that if considering a microbiome’s causality in the host as an ecosystem, its etiological explanation needs to be revisited to include a heterogeneous and mutual notion of interactions. Finally, according to the second point, the notion of function in ecology with its relevant notion of causality should be considered accordingly. (shrink)

Recent philosophical work on causation has focused on distinctions across types of causal relationships. This paper argues for another distinction that has yet to receive attention in this work. This distinction has to do with whether causal relationships have “material continuity,” which refers to the reliable movement of material from cause to effect. This paper provides an analysis of material continuity and argues that causal relationships with this feature are associated with a unique explanatory perspective, are studied with distinct causal (...) investigative methods, and provide different types of causal control over their effects. (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)

According to a shared functionalist view in philosophy of mind, a cognitive system, and cognitive function thereof, is based on the components of the organism it is realized by which, indeed, play a causal role in regulating our cognitive processes. This led philosophers to suggest also that, thus, cognition could be seen as an extended process, whose vehicle can extend not only outside the brain but also beyond bodily boundaries, on different kinds of devices. This is what we call the (...) ‘Externally Extended Cognition Thesis.’ This notion has generated a lively debate. Here, we offer a novel notion of extended cognition, according to which cognition can be seen as being realized outside the brain, but still inside the body. This is what we call the ‘Internally Extended Cognition Thesis’. Not only our thesis but also our approach while defending it is innovative. The argument we offer is supported by recent empirical findings in the life sciences and biomedicine, which suggest that the gut microbiota’s activity has a functional role in regulating our cognitive processes and behaviors. In doing so, we embrace the holobiont-perspective, according to which it is possible to claim that what we call biological individuals are not autonomous entities with clear boundaries, but should rather be seen as networks of multiple interactions among species. Thus, by analyzing different sets of evidence in light of the holobiont-perspective, we argue that the gut microbiota could be seen as a component of our organism. On the basis of the philosophical interpretation of this evidence, however, we also suggest that there are no impediments standing the way of considering the gut microbiota also as a functional extension of our cognitive system. If so, this amounts to extending cognition out of ‘our skull’, though still confining it within ‘our body’: to ‘our gut’. This is an instance of the ‘Internally Extended Cognition Thesis,’ whose benefits for an original theory of extended cognition are discussed. (shrink)

Lynch et al. (Biol Philos 34:62, 2019) employ stability, specificity, and proportionality as criteria for evaluating microbiome causal explanations. Although these causal characteristics signify relevant differences between causal roles, I suggest that they should not be used as general criteria for strong or good causal explanations.

In our commentary on Lynch et al.’s target paper, we focus on decomposition as a research strategy. We argue that not only the presumptive microbial causes but also their supposed phenotypic effects need to be decomposed relative to each other. Such a dual decomposition strategy ought to improve the way in which causal claims in microbiome research can be made and understood.

In their paper “How Causal are Microbiomes? A Comparison with the Helicobacter pylori Explanation of Ulcers,” Lynch, Parke, and O’Malley successfully argue that certain causal attributions made to the microbiome have not satisfied Koch’s postulates nor the interventionist framework. However, their argument involves an implicit assumption that cases such as H. pylori are sufficiently similar to cases involving the microbiome, such that causal attributions to both should be evaluated according to the same causal framework. Our commentary targets this assumption. First, (...) we introduce the historical circumstances that led to the formulation of Koch’s postulates in order to differentiate the case of the microbiome from that of infectious bacteria. Then, we introduce the concept of the holobiont, the idea that hosts and their symbionts should be conceptualized as a metaphysical and biological unit. Finally, using the holobiont concept, we argue that Koch’s postulates and the interventionist framework are ill-equipped to handle the microbiome. We conclude by suggesting that a revision of what counts as microbiological causality within the holobiont is justified. (shrink)

Emphatic claims of a “microbiome revolution” aside, the study of the gut microbiota and its role in organismal development and evolution is a central feature of so-called postgenomics; namely, a conceptual and/or practical turn in contemporary life sciences, which departs from genetic determinism and reductionism to explore holism, emergentism and complexity in biological knowledge-production. This paper analyses the making of postgenomic knowledge about developmental symbiosis in Drosophila melanogaster by a specific group of microbiome scientists. Drawing from both practical philosophy of (...) science and Science and Technology Studies, the paper documents epistemological questions of artefactuality and representativeness of model organisms as they emerge in the day-to-day labour producing and being produced by the “microbiome revolution." Specifically, the paper builds on all the written and editorial exchanges involved in the troubled publication of a research paper studying the symbiotic role of the microbiota in the flies’ development. These written materials permit us to delimit the network of justifications, evidence, standards of knowledge-production, trust in the tools and research designs that make up the conditions of possibility of a postgenomic fact. More than reframing the organism as a radically novel multiplicity of reactive genomes, we conclude, doing postgenomic research on the microbiota and symbiosis means producing a story that deviates from the scripts embedded into the sociotechnical experimental systems of post-Human Genome Project life sciences. (shrink)

We are less optimistic than Madole & Harden that family-based genome-wide association studies (GWASs) will lead to significant second-generation causal knowledge. Despite bearing some similarities, family-based GWASs and randomised controlled trials (RCTs) are not identical. Most RCTs assess a relatively homogenous causal stimulus as a treatment, whereas GWASs assess highly heterogeneous causal stimuli. Thus, GWAS results will not translate so easily into second-generation causal knowledge.

Lynch et al. propose an extremely useful framework to assess microbiome research. By utilising advances in the causation literature, they argue that many of the claims in microbiome research are ‘weak or misleading’ as these claims lack stability, specificity, or proportionality. In the final paragraph before the conclusion they entertain and rapidly dismiss the ‘ecological version’ of microbiomes, in which microbiome properties are emergent from their constituent populations and can fulfil Koch’s postulates. I assess the possibility of microbiomes having emergent (...) causal efficacy on host health and suggest they can. (shrink)

Various scientists and philosophers have heavily criticized what they see as problematic forms of ‘nutritional reductionism’ or ‘nutritionism’ whereby studying food–health interactions at the level of isolated food components produces largely misguided science and misleading interpretations. However, the exact target of these diverse criticisms remains elusive, and its implications are overstated, which may hinder scientific understanding. To better identify the types of flaws supposedly hindering reductionist research, we disentangle three types of reductionist claims to better determine what the debate is (...) about and to propose ways to move it forward. We then present a qualified defence of the reductionist programme that hinges on the ability to identify nutritional causes that make a difference, which we illustrate through central examples in the history of nutrition. This defence is taken further by using insights from the philosophy of mechanisms to analyse how the field of nutritional ecology offers a synthetic framework to explain, generate, and test predictions about nutrient–organism interactions, which is premised on the biological mechanisms of nutrient-specific appetite regulation. The result, which we call ‘synthetic reductionism’, avoids many, though perhaps not all, of the challenges raised by anti-reductionists, and also highlights the potential of reductionism to identify nutritional difference makers. (shrink)

The aim of the present paper is to explore whether seasonal outbreaks of infectious diseases may be linked to changes in host microbiomes. This is a very important issue, because one way to have more control over seasonal outbreaks is to understand the factors that underlie them. In this paper, I will evaluate the relevance of the microbiome as one of such factors. The paper is based on two pillars of reasoning. Firstly, on the idea that microbiomes play an important (...) role in their hosts’ defence against infectious diseases. Secondly, on the idea that microbiomes are not stable, but change seasonally. These two ideas are combined in order to argue that seasonal changes in a given microbiome may influence the functionality of the host's immune system and consequently make it easier for infectious agents to infect the host at certain times of year. I will argue that, while this is only a theoretical possibility, certain studies may back up such claims. Furthermore, I will show that this does not necessarily contradict other hypotheses aimed at explaining seasonal outbreaks; in fact, it may even enhance them. (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)

Our analysis of microbiota-gut-brain research took MGB to task for some of its methods, concepts, and interpretations. Commentators then raised numerous issues about the neuroscientific and microbiome aspects of MGB and how it can be understood as a field. We respond by addressing the dimensionality and causal focus of MGB.

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)

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)

A distinction between different notions of “structure” and “function” is suggested for interpreting the overwhelming amount of data on microbiome structure and function. Sequence data, biochemical agents, interaction networks, taxonomic communities, and their dynamics can be linked to potential or actual biochemical activities, causal roles, and selected effects, respectively. This conceptual clarification has important methodological consequences for how to interpret existing data and approach open questions in contemporary microbiome research practice. In particular, the field will have to start thinking about (...) notions of function more directly. Also see the video abstract here https://youtu.be/j5pq5uGld1k. (shrink)

Systems biology is the rapidly growing and heavily funded successor science to genomics. Its mission is to integrate extensive bodies of molecular data into a detailed mathematical understanding of all life processes, with an ultimate view to their prediction and control. Despite its high profile and widespread practice, there has so far been almost no bioethical attention paid to systems biology and its potential social consequences. We outline some of systems biology's most important socioethical issues by contrasting the concept of (...) systems as dynamic processes against the common static interpretation of genomes. New issues arise around systems biology's capacities for in silico testing, changing cultural understandings of life, synthetic biology, and commercialization. We advocate an interdisciplinary and interactive approach that integrates social and philosophical analysis and engages closely with the science. Overall, we argue that systems biology socioethics could stimulate new ways of thinking about socioethical studies of life sciences. (shrink)

Experimental manipulations are a key means to establish causal relationships in microbiology. However, challenges remain to establish the applicability of such experiments beyond the precise conditions in which they were conducted. Ecological information can help address these challenges by describing the extent to which an experimentally-determined mechanism can explain the natural phenomenon that it is purported to cause.