This article offers a critical reflection on the role of mathematical modelling in futures studies. It is written by members of the Futures editorial team and intended to guide authors interested in submitting papers on the formal modelling of futures to the journal. While models are increasingly prominent in shaping visions of the future across science, policy, and society, their use raises fundamental concerns. The paper outlines three key challenges: the limitations of models in handling novelty and surprise, their counter-performative effects in shaping rather than simply anticipating futures, and the epistemological consequences of their dominance in evidence-based policymaking. Drawing on critiques from science and technology studies, economics, and complexity theory, the authors argue for a more reflexive, inclusive, and pluralistic approach to modelling. They propose six guiding principles—transparency, reflexivity, inclusivity, complexity (not complicatedness), relevance over precision, and contribution—to guide submissions to Futures. The goal is to ensure that modelling contributes meaningfully to the field’s core mission: the collective construction of better futures, and to help authors in writing papers that are appropriately reflexive towards the use of models in futures work.

Plasmids are major drivers of microbial evolution, enabling horizontal gene transfer (HGT) and facilitating adaptation through the dissemination of relevant functional genes and traits. However, little is known about plasmid diversity and function in extremophiles. ‘Fervidacidithiobacillus caldus’, a meso-thermo-acidophilic sulfur oxidizer, is a key player in sulfur cycling in natural and industrially engineered acidic environments. Here, we present a bioinformatic analysis of the plasmidome, and associated anti-mobile genetic element (anti-MGE) defense systems (defensome), across genomes of this species and metagenomes from diverse natural and industrial settings harboring ‘F. caldus’. We identified >30 distinct plasmids, representing five consistent replication-mobilization families. Plasmids ranged in size between 2.5–65 kb, with gene content and plasmid modularity scaling with element size and copy numbers inversely correlating with size. Plasmids carried variable numbers of hypothetical proteins and transposases, with annotated cargo genes reflecting functional differentiation by habitat. Defensome profiling revealed over 50 anti-MGE systems in sequenced ‘F. caldus’ isolates, including diverse restriction-modification systems, CRISPR-Cas types IV-A and V-F, and widespread abortive infection and composite defense systems such as Wadjet, Gabija, and Zorya. In environmental populations, an inverse relationship was observed between defensome complexity and plasmidome abundance and diversity, underscoring a pivotal role of the host defensome in modulating persistence, compatibility, and overall plasmid diversity across ‘F. caldus’ populations. Yet, other plasmids appeared decoupled from both host abundance and defensome complexity, suggesting potential host shifts, environmental persistence, or differential replication under suboptimal growth conditions for the host. Altogether, these findings point to a modular, functionally diverse adaptive plasmidome shaped by environmental pressures, by the interplay with the host’s defensome, and likely also by other eco-evolutionary processes at play in natural environments. While these associations are compelling, causal relationships remain to be experimentally validated. These insights broaden our understanding of mobile genetic elements in extreme environments and provide a foundation for plasmid-based vector design and synthetic biology applications in acidophiles, with direct implications to biomining and environmental remediation.

Plasmids are major drivers of microbial evolution, enabling horizontal gene transfer (HGT) and facilitating adaptation through the dissemination of relevant functional genes and traits. However, little is known about plasmid diversity and function in extremophiles. ‘ Fervidacidithiobacillus caldus’, a meso-thermo-acidophilic sulfur oxidizer, is a key player in sulfur cycling in natural and industrially engineered acidic environments. Here, we present a comprehensive analysis of the plasmidome, and associated anti-mobile genetic element (anti-MGE) defense systems (defensome), across genomes of this species and metagenomes from diverse natural and industrial settings harboring ‘ F. caldus’ . We identified >30 distinct plasmids, representing five consistent replication-mobilization families. Plasmids ranged in size between 2.5–65 kb, with gene content and plasmid modularity scaling with element size and copy numbers inversely correlating with size. Plasmids carried variable numbers of hypothetical proteins and transposases, with annotated cargo genes reflecting functional differentiation by habitat. Defensome profiling revealed over 50 anti-MGE systems in sequenced ‘ F. caldus’ isolates, including diverse restriction-modification systems, CRISPR-Cas types IV-A and V-F, and widespread abortive infection and composite defense systems such as Wadjet, Gabija, and Zorya. In environmental populations, an inverse relationship was observed between defensome complexity and plasmidome abundance and diversity, underscoring a pivotal role of the host defensome in modulating persistence, compatibility, and overall plasmid diversity across ‘ F. caldus’ populations. Yet, other plasmids appeared decoupled from both host abundance and defensome complexity, suggesting potential host shifts, environmental persistence, or differential replication under suboptimal growth conditions for the host. Altogether, these findings reveal a modular, adaptive plasmidome shaped by selective pressures and host–plasmid–defensome interactions and positions plasmids as key contributors to adaptation, gene flow, and functional innovation in this extreme acidophile. Importance Plasmids are key vehicles of gene exchange and adaptation in bacteria, yet their roles in extremophilic systems remain poorly understood. This study provides the first integrated view of the plasmidome and defense systems in ‘ Fervidacidithiobacillus caldus’ , a sulfur-oxidizing acidophile relevant to both natural biogeochemical cycling and industrial bioleaching. We uncover a rich plasmid diversity structured into modular families with variable cargo and backbone features and reveal their coexistence with complex anti-MGE defense repertoires. By combining genomic and metagenomic approaches, we expose principles of plasmid compatibility, persistence, and habitat-specific adaptation. These insights expand current knowledge of mobile genetic elements in extreme environments and provide a foundation for plasmid-based vector design and synthetic biology in acidophiles, with direct implications for biomining and environmental remediation in extreme environments.

Evaluators’ main encounter with views of the future is in the form of theories of change, about how a programme will work to achieve a desired end, in a given context. These are typically focussed on specific relatively short-term futures, which are both desired and expected. But even in the short term, reality often involves unpredictable events which must be responded to. Other ways of thinking about the future may be helpful and complementary, notably those developed by foresight practitioners working in the field of futures studies. These pay more attention to a range of possible futures, rather than a single perspective. One way of exploring such futures is by using ParEvo.org, an online process that enables the participatory exploration of alternative futures. This article explains how the ParEvo process works, the theory informing its design, and its usage to date. Attention is given to three evaluation challenges, and methods to address them: (a) optimising exercise design, (b) analysis of immediate results and (c) identifying longer-term impacts. Two exercises undertaken by the Cambridge-based Centre for the Study of Existential Risk (CSER) in 2021–2022 are used as illustrative examples.

Focusing on the study of existential risk, this chapter shows how academic research publications can be systematically reviewed using semi-automated processes such as crowdsourcing and machine learning. These publications can then be accumulated in an open-access database, if relevant, forming a reusable evidence base for policy and risk analysis. The authors use The Existential Risk Research Assessment (TERRA), a living bibliography about existential risk, as an example of the semi-automated processes in action, noting the successes and challenges of such a semi-automated tool. This chapter allows for speculation concerning the future of a publication base like TERRA and the authors encourage readers themselves to participate in TERRA, to contribute to a bigger and better future bibliography.

Membrane vesicles (MVs) are envelope-derived extracellular sacs that perform a broad diversity of physiological functions in bacteria. While considerably studied in pathogenic microorganisms, the roles, relevance, and biotechnological potential of MVs from environmental bacteria are less well established. Acidithiobacillaceae family bacteria are active players in the sulfur and iron biogeochemical cycles in extremely acidic environments and drivers of the leaching of mineral ores contributing to acid rock/mine drainage (ARD/AMD) and industrial bioleaching. One key aspect of such a role is the ability of these bacteria to tightly interact with the mineral surfaces and extract electrons and nutrients to support their chemolithotrophic metabolism. Despite recent advances in the characterization of acidithiobacilli biofilms and extracellular matrix (ECM) components, our understanding of its architectural and mechanistic aspects remains scant. Using different microscopy techniques and nano-tracking analysis we show that vesiculation is a common phenomenon in distant members of the Acidithiobacillaceae family, and further explore the role of MVs in multicellular colonization behaviors using ‘Fervidacidithiobacillus caldus’ as a bacterial model. Production of MVs in ‘F. caldus’ occurred in both planktonic cultures and biofilms formed on sulfur surfaces, where MVs appeared individually or in chains resembling tube-shaped membranous structures (TSMSs) important for microbial communication. Liquid chromatography–mass spectrometry data and bioinformatic analysis of the MV-associated proteome revealed that ‘F. caldus’ MVs were enriched in proteins involved in cell–cell and cell–surface processes and largely typified the MVs as outer MVs (OMVs). Finally, microbiological assays showed that amendment of ‘F. caldus’ MVs to cells and/or biofilms affects collective colonizing behaviors relevant to the ecophysiology and applications of these acidophiles, providing grounds for their exploitation in biomining.

Mobile genetic elements (MGEs) are relevant agents in bacterial adaptation and evolutionary diversification. Stable appropriation of these DNA elements depends on host factors, among which are the nucleoid-associated proteins (NAPs). NAPs are highly abundant proteins that bind and bend DNA, altering its topology and folding, thus affecting all known cellular DNA processes from replication to expression. Even though NAP coding genes are found in most prokaryotic genomes, their functions in host chromosome biology and xenogeneic silencing are only known for a few NAP families. Less is known about the occurrence, abundance, and roles of MGE-encoded NAPs in foreign elements establishment and mobility. In this study, we used a combination of comparative genomics and phylogenetic strategies to gain insights into the diversity, distribution, and functional roles of NAPs within the class Acidithiobacillia with a special focus on their role in MGE biology. Acidithiobacillia class members are aerobic, chemolithoautotrophic, acidophilic sulfur-oxidizers, encompassing substantial genotypic diversity attributable to MGEs. Our search for NAP protein families (PFs) in more than 90 genomes of the different species that conform the class, revealed the presence of 1,197 proteins pertaining to 12 different NAP families, with differential occurrence and conservation across species. Pangenome-level analysis revealed 6 core NAP PFs that were highly conserved across the class, some of which also existed as variant forms of scattered occurrence, in addition to NAPs of taxa-restricted distribution. Core NAPs identified are reckoned as essential based on the conservation of genomic context and phylogenetic signals. In turn, various highly diversified NAPs pertaining to the flexible gene complement of the class, were found to be encoded in known plasmids or, larger integrated MGEs or, present in genomic loci associated with MGE-hallmark genes, pointing to their role in the stabilization/maintenance of these elements in strains and species with larger genomes. Both core and flexible NAPs identified proved valuable as markers, the former accurately recapitulating the phylogeny of the class, and the later, as seed in the bioinformatic identification of novel episomal and integrated mobile elements.

We report the results of a structured expert elicitation to identify the most likely types of potential food system disruption scenarios for the UK, focusing on routes to civil unrest. We take a backcasting approach by defining as an end-point a societal event in which 1 in 2000 people have been injured in the UK, which 40% of experts rated as “Possible (20–50%)”, “More likely than not (50–80%)” or “Very likely (>80%)” over the coming decade. Over a timeframe of 50 years, this increased to 80% of experts. The experts considered two food system scenarios and ranked their plausibility of contributing to the given societal scenario. For a timescale of 10 years, the majority identified a food distribution problem as the most likely. Over a timescale of 50 years, the experts were more evenly split between the two scenarios, but over half thought the most likely route to civil unrest would be a lack of total food in the UK. However, the experts stressed that the various causes of food system disruption are interconnected and can create cascading risks, highlighting the importance of a systems approach. We encourage food system stakeholders to use these results in their risk planning and recommend future work to support prevention, preparedness, response and recovery planning.

The recent revision of the Acidithiobacillia class using genomic taxonomy methods has shown that, in addition to the existence of previously unrecognized genera and species, some species of the class harbor levels of divergence that are congruent with ongoing differentiation processes. In this study, we have performed a subspecies-level analysis of sequenced strains of Acidithiobacillus ferrooxidans to prove the existence of distinct sublineages and identify the discriminant genomic/genetic characteristics linked to these sublineages, and to shed light on the processes driving such differentiation. Differences in the genomic relatedness metrics, levels of synteny, gene content, and both integrated and episomal mobile genetic elements (MGE) repertoires support the existence of two subspecies-level taxa within A. ferrooxidans. While sublineage 2A harbors a small plasmid related to pTF5, this episomal MGE is absent in sublineage 2B strains. Likewise, clear differences in the occurrence, coverage and conservation of integrated MGEs are apparent between sublineages. Differential MGE-associated gene cargo pertained to the functional categories of energy metabolism, ion transport, cell surface modification, and defense mechanisms. Inferred functional differences have the potential to impact long-term adaptive processes and may underpin the basis of the subspecies-level differentiation uncovered within A. ferrooxidans. Genome resequencing of iron- and sulfur-adapted cultures of a selected 2A sublineage strain (CCM 4253) showed that both episomal and large integrated MGEs are conserved over twenty generations in either growth condition. In turn, active insertion sequences profoundly impact short-term adaptive processes. The ISAfe1 element was found to be highly active in sublineage 2A strain CCM 4253. Phenotypic mutations caused by the transposition of ISAfe1 into the pstC2 encoding phosphate-transport system permease protein were detected in sulfur-adapted cultures and shown to impair growth on ferrous iron upon the switch of electron donor. The phenotypic manifestation of the △pstC2 mutation, such as a loss of the ability to oxidize ferrous iron, is likely related to the inability of the mutant to secure the phosphorous availability for electron transport-linked phosphorylation coupled to iron oxidation. Depletion of the transpositional △pstC2 mutation occurred concomitantly with a shortening of the iron-oxidation lag phase at later transfers on a ferrous iron-containing medium. Therefore, the pstII operon appears to play an essential role in A. ferrooxidans when cells oxidize ferrous iron. Results highlight the influence of insertion sequences and both integrated and episomal mobile genetic elements in the short- and long-term adaptive processes of A. ferrooxidans strains under changing growth conditions.

This paper presents a collaborative exercise to explore divergent futures for the field of global risk, and especially the global risk community intersecting with the Centre for the Study of Existential Risk at the University of Cambridge. While this community often advocates for the value of futures and foresight to others, we believe this is the first attempt to use these same techniques to think about our own futures and the opportunities and challenges they may bring. The paper begins by setting out the nature of the global risk community, the ParEvo process that was applied, and the background to this specific exercise. Next, we offer a more in-depth presentation of the methods used, both to undertake the exercise itself, analyse and evaluate its results, and theorize about what these mean. We then offer a brief presentation of key results and themes that originated from this exercise, including summaries of the stories produced and how these were evaluated by participants, and focused results across three core themes 'conflict and rapprochement, agents of change, and story outcomes and impacts. Finally, we discuss the exercise's limitations and challenges and possible lessons, both for the application of ParEvo and other futures tools (including the benefits of participatory exercise design and more detailed and ongoing evaluation of contributions) and for the global risk community as it seeks to grow and develop (including the need for conflict resolution mechanisms, greater planning about how global risk research may interact with actual global risk, and more reflection on what the community aims to achieve and how to assess whether we are making progress. Full results from the exercise are presented in a detailed appendix.

One of Derek Parfit’s greatest legacies was the search for Theory X, a theory of population ethics that avoided all the implausible conclusions and paradoxes that have dogged the field since its inception: the Absurd Conclusion, the Repugnant Conclusion, the Non-Identity Problem, and the Mere Addition Paradox. In recent years, it has been argued that this search is doomed to failure and no satisfactory population axiology is possible. This chapter reviews Parfit’s life’s work in the field and argues that he provided all the necessary components necessary for a Theory X. It then shows how these components can be combined together and applied to the global challenges Parfit argued matter most: preventing human extinction, managing catastrophic risks, and eradicating global poverty and suffering. Finally, it identifies a number of challenges facing his theory and suggests how these may be overcome.

Societal biosecurity – measures built into everyday society to minimize risks from pests and diseases – is an important aspect of managing epidemics and pandemics. We aimed to identify societal options for reducing the transmission and spread of respiratory viruses. We used SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) as a case study to meet the immediate need to manage the COVID-19 pandemic and eventually transition to more normal societal conditions, and to catalog options for managing similar pandemics in the future. We used a ‘solution scanning’ approach. We read the literature; consulted psychology, public health, medical, and solution scanning experts; crowd-sourced options using social media; and collated comments on a preprint. Here, we present a list of 519 possible measures to reduce SARS-CoV-2 transmission and spread. We provide a long list of options for policymakers and businesses to consider when designing biosecurity plans to combat SARS-CoV-2 and similar pathogens in the future. We also developed an online application to help with this process. We encourage testing of actions, documentation of outcomes, revisions to the current list, and the addition of further options.

Members of the genus Acidithiobacillus, now ranked within the class Acidithiobacillia, are model bacteria for the study of chemolithotrophic energy conversion under extreme conditions. Knowledge of the genomic and taxonomic diversity of Acidithiobacillia is still limited. Here, we present a systematic analysis of nearly 100 genomes from the class sampled from a wide range of habitats. Some of these genomes are new and others have been reclassified on the basis of advanced genomic analysis, thus defining 19 Acidithiobacillia lineages ranking at different taxonomic levels. This work provides the most comprehensive classification and pangenomic analysis of this deep-branching class of Proteobacteria to date. The phylogenomic framework obtained illuminates not only the evolutionary past of this lineage, but also the molecular evolution of relevant aerobic respiratory proteins, namely the cytochrome bo3 ubiquinol oxidases.

Many have claimed that climate change is an imminent threat to humanity, but there is no way to verify such claims. This is concerning, especially given the prominence of some of these claims and the fact that they are confused with other well verified and settled aspects of climate science. This paper seeks to build an analytical framework to help explore climate change's contribution to Global Catastrophic Risk (GCR), including the role of its indirect and systemic impacts. In doing so it evaluates the current state of knowledge about catastrophic climate change and integrates this with a suite of conceptual and evaluative tools that have recently been developed by scholars of GCR and Existential Risk. These tools connect GCR to planetary boundaries, classify its key features, and place it in a global policy context. While the goal of this paper is limited to producing a framework for assessment; we argue that applying this framework can yield new insights into how climate change could cause global catastrophes and how to manage this risk. We illustrate this by using our framework to describe the novel concept of possible' global systems death spirals,' involving reinforcing feedback between collapsing sociotechnological and ecological systems.

Undoubtedly, many of the most pressing problems of our age relate to changes in human population. Population growth and demographic transition are having profound social (Lutz, 2014), economic (Sin...

We welcome Seth Baum's reply to our paper. We broadly agree with the points Baum makes; however, the field of Existential Risk Studies remains young and undeveloped, and we think that there are many points on which further reflection is needed. We briefly discuss three: the normative aspects of terms like 'existential catastrophe,' the opportunities for low hanging fruit in method selection and application, and the importance of context when making probability claims.

● The mental health impacts of COVID-19 are expected to be very significant and could be the single greatest health burden caused by this pandemic in the long term. However, at present they are not being assessed at the population level, while not enough is being done to study these impacts and how to respond to them. As with other aspects of this pandemic, we cannot address the mental health impacts of COVID-19 without better data and more research.

The study of existential risk — the risk of human extinction or the collapse of human civilization — has only recently emerged as an integrated field of research, and yet an overwhelming volume of relevant research has already been published. To provide an evidence base for policy and risk analysis, this research should be systematically reviewed. In a systematic review, one of many time-consuming tasks is to read the titles and abstracts of research publications, to see if they meet the inclusion criteria. We show how this task can be shared between multiple people (using crowdsourcing) and partially automated (using machine learning), as methods of handling an overwhelming volume of research. We used these methods to create The Existential Risk Research Assessment (TERRA), which is a living bibliography of relevant publications that gets updated each month (www.x-risk.net). We present the results from the first ten months of TERRA, in which 10,001 abstracts were screened by 51 participants. Several challenges need to be met before these methods can be used in systematic reviews. However, we suggest that collaborative and cumulative methods such as these will need to be used in systematic reviews as the volume of research increases.

The Repugnant Conclusion and its paradoxes pose a significant problem for outcome evaluation. Derek Parfit has suggested that we may be able to resolve this problem by accepting a view he calls ‘Perfectionism’, which gives lexically superior value to ‘the best things in life’. In this paper, I explore perfectionism and its potential to solve this problem. I argue that perfectionism provides neither a sufficient means of avoiding the Repugnant Conclusion nor a full explanation of its repugnance. This is because even lives that are ‘barely worth living’ may contain the best things in life if they also contain sufficient ‘bad things’, such as suffering or frustration. Therefore, perfectionism can only fully explain or avoid the Repugnant Conclusion if combined with other claims, such as that bad things have an asymmetrical value relative to many good things. This combined view faces the objection that any such asymmetry implies Parfit’s ‘Ridiculous Conclusion’. However, I argue that perfectionism itself faces very similar objections, and that these are question-begging against both views. Finally, I show how the combined view that I propose not only explains and avoids the Repugnant Conclusion but also allows us to escape many of its paradoxes as well.