Reintroducing group selection to the human behavioral sciences

Bring back the phenotype

When thinking about evolutionary change, many practicing biologists will focus on changes in allele frequencies over time. This gene-centric view of evolution has strongly impacted how evolution (and biological science in general) is thought of, taught, and funded. In this viewpoint, we join recent criticisms of the gene-centric view and call for reinstalling a phenotypic view of evolution. The assumptions of the gene-centric view-enormous/nonstructured populations and totally random interactions between genes, individuals, and environments-are hard to imagine in the real world. A gene's effects on phenotype and fitness depend on its interactions with other genes (epistasis), other individuals, the microbiome, and the environment, and it changes between generations, populations, and environments. Incorrectly, genes have been given an agency and role in natural selection that they do not possess: they replicate, but they do not have phenotypic variation or differential proliferation through their traits (these are characteristics of the units of selection deemed 'interactors'). Here, we show how a phenotypic view of evolution is necessary to capture several widespread phenomena: epistasis, nongenetic inheritance, multilevel selection, and niche construction through plant-soil feedbacks, all of which have vast empirical evidence. Life is marvelous, complex, and certainly more than machinery and genetic information.

Exploring the Evolution of Altruistic Punishment with a PDE Model of Cultural Multilevel Selection

Two mechanisms that have been used to study the evolution of cooperative behavior are altruistic punishment, in which cooperative individuals pay additional costs to punish defection, and multilevel selection, in which competition between groups can help to counteract individual-level incentives to cheat. Boyd, Gintis, Bowles, and Richerson have used simulation models of cultural evolution to suggest that altruistic punishment and pairwise group-level competition can work in concert to promote cooperation, even when neither mechanism can do so on its own. In this paper, we formulate a PDE model for multilevel selection motivated by the approach of Boyd and coauthors, modeling individual-level birth-death competition with a replicator equation based on individual payoffs and describing group-level competition with pairwise conflicts based on differences in the average payoffs of the competing groups. Building off of existing PDE models for multilevel selection with frequency-independent group-level competition, we use analytical and numerical techniques to understand how the forms of individual and average payoffs can impact the long-time ability to sustain altruistic punishment in group-structured populations. We find several interesting differences between the behavior of our new PDE model with pairwise group-level competition and existing multilevel PDE models, including the observation that our new model can feature a non-monotonic dependence of the long-time collective payoff on the strength of altruistic punishment. Going forward, our PDE framework can serve as a way to connect and compare disparate approaches for understanding multilevel selection across the literature in evolutionary biology and anthropology.

Multilevel selection on individual and group social behaviour in the wild

How phenotypes are shaped by multilevel selection-the theoretical framework proposing natural selection occurs at more than one level of biological organization-is a classic debate in biology. Though social behaviours are a common theoretical example for multilevel selection, it is unknown if and how multilevel selection acts on sociality in the wild. We studied the relative strength of multilevel selection on both individual behaviour and group social structure, quantified with social networks and 19 years of data from a wild, free-living mammal, the yellow-bellied marmot (Marmota flaviventer). Contextual analysis (exploring the impact of individual and group social phenotypes on individual fitness, relative to each other) revealed multilevel selection gradients in specific fitness and life history contexts, with selection for group social structure being just as strong, if not stronger, than individual social behaviour. We also found antagonistic multilevel selection gradients within and between levels, potentially explaining why increased sociality is not as beneficial or heritable in this system compared with other social taxa. Thus, the evolutionary dynamics of hierarchical or nested biological traits should be assessed at multiple levels simultaneously to tell a more accurate and comprehensive story. Overall, we provide empirical evidence suggesting that multilevel selection acts on social relationships and structures in the wild and provide direct evidence for a classic, unanswered question in biology.

Using Latent Class Analysis to Characterize Sickness Signaling in Relation to Familism and Public and Private Religiosity in a Stratified US Sample

BACKGROUND

In response to contracting an infection, individuals usually display a suite of external signs (including sickness behavior) as an outward indication of illness. This context-dependent phenomenon seems to weigh the benefits and costs of eliciting sympathy by indicating sickness versus hiding signs of illness to avoid exposing others to potential infection. In a dynamically social species like humans, non-kin may be as likely to respond to these signs with care as family members, particularly fellow church members. We explore the relative contributions of religiosity and familism in shaping self-reported sickness signaling styles as two dimensions central to human altruism using latent class analysis (LCA).

METHODS

LCA was used to characterize the signaling styles of the study participants. Data come from a large 2018 survey (n = 1259) of sickness and health behaviors among US adults. We used denomination public (church attendance) and private religiosity (time spent in prayer, meditation, etc.) and the God Locus of Health Control scale to assess the impact of God on health. Sickness signaling style was assessed with the SicknessQ and three additional items. Covariates included age, gender, education, and income.

RESULTS

We identified four classes (Familiar, Moderate, Gregarious, and Stoic) tied to signaling styles. The Familiar Signaling class displayed sickness verbally to familiar others, were the oldest, and were least guided by an internal sense of religion. The Moderate Signaling class was younger and had lower public and private religiosity (except regarding health issues) than the Stoic and Gregarious Signaling classes. The Gregarious class signaled to both close others and strangers and scored highest in familism and religiosity. The Stoic class did not verbally signal but indicated sickness worsening when around both close others and strangers, were less likely to be married or endorse private religiosity, and were least likely to recall recent illness as severe.

CONCLUSION

The signaling classes strongly resembled aspects of the introvert-ambivert-extrovert spectrum. We conclude that variation is important at multiple levels, including personality types, and potentially prevents the loss of immunological diversity.

Stability of ecologically scaffolded traits during evolutionary transitions in individuality

Evolutionary transitions in individuality are events in the history of life leading to the emergence of new levels of individuality. Recent studies have described an ecological scaffolding scenario of such transitions focused on the evolutionary consequences of an externally imposed renewing meta-population structure with limited dispersal. One difficulty for such a scenario has been explaining the stability of collective-level traits when scaffolding conditions no longer apply. Here, we show that the stability of scaffolded traits can rely on evolutionary hysteresis: even if the environment is reverted to an ancestral state, collectives do not return to ancestral phenotypes. We describe this phenomenon using a stochastic meta-population model and adaptive dynamics. Further, we show that ecological scaffolding may be limited to Goldilocks zones of the environment. We conjecture that Goldilocks zones-even if they might be rare-could act as initiators of evolutionary transitions and help to explain the near ubiquity of collective-level individuality.

Nonlinear eco-evolutionary games with global environmental fluctuations and local environmental feedbacks

Environmental changes play a critical role in determining the evolution of social dilemmas in many natural or social systems. Generally, the environmental changes include two prominent aspects: the global time-dependent fluctuations and the local strategy-dependent feedbacks. However, the impacts of these two types of environmental changes have only been studied separately, a complete picture of the environmental effects exerted by the combination of these two aspects remains unclear. Here we develop a theoretical framework that integrates group strategic behaviors with their general dynamic environments, where the global environmental fluctuations are associated with a nonlinear factor in public goods game and the local environmental feedbacks are described by the 'eco-evolutionary game'. We show how the coupled dynamics of local game-environment evolution differ in static and dynamic global environments. In particular, we find the emergence of cyclic evolution of group cooperation and local environment, which forms an interior irregular loop in the phase plane, depending on the relative changing speed of both global and local environments compared to the strategic change. Further, we observe that this cyclic evolution disappears and transforms into an interior stable equilibrium when the global environment is frequency-dependent. Our results provide important insights into how diverse evolutionary outcomes could emerge from the nonlinear interactions between strategies and the changing environments.

Reticulate evolution underlies synergistic trait formation in human communities

This paper investigates how reticulate evolution contributes to a better understanding of human sociocultural evolution in general, and community formation in particular. Reticulate evolution is evolution as it occurs by means of symbiosis, symbiogenesis, lateral gene transfer, infective heredity, and hybridization. From these mechanisms and processes, we mainly zoom in on symbiosis and we investigate how it underlies the rise of (1) human, plant, animal, and machine interactions typical of agriculture, animal husbandry, farming, and industrialization; (2) diet-microbiome relationships; and (3) host-virome and other pathogen interactions that underlie human health and disease. We demonstrate that reticulate evolution necessitates an understanding of behavioral and cultural evolution at a community level, where reticulate causal processes underlie the rise of synergistic organizational traits.

Faustian bargains: Short-term and long-term contingencies in phylogeny, ontogeny, and sociogeny

Rachlin's interpretations of self-control depend on the short-term versus the long-term consequences of behavior. Sometimes these effects support each other (typing an abstract produces a written product now and is later read by others). Sometimes they conflict (procrastination now is incompatible with finishing the abstract by deadline). We usually reserve the language of self-control for human cases where long-term consequences are chosen over short-term ones. Rachlin made this distinction salient in ontogeny, but it also applies to selection in phylogeny (Darwinian evolution) and sociogeny (behavior passed from one organism to another). Our account examines relations between short-term and long-term consequences at each level of selection. For example, sexual selection has adaptive, short-term mating consequences but may drive species to extreme specializations that jeopardize long-term survival. In sociogeny, as in the Tragedy of the Commons, group members may get immediate economic benefits from exploiting resources but exhaust those resources over the long term. Whatever the level, when short-term and long-term consequences have opposing effects, adaptive behavior may depend on whether temporally extended contingencies exert more control than more immediate benefits.

How Awe Shaped Us: An Evolutionary Perspective

Research shows the experience of awe is associated with a variety of benefits ranging from increased well-being and prosocial behavior to enhanced cognition. The adaptive purpose of awe, however, is elusive. In this article, we aim to show that the current framework used to conceptualize awe points towards higher-order cognition as the key adaptive function. This goes against past evolutionary positions that posit social benefits or unidimensional behavioral adaptations. In the second half of the article, we highlight a distinct cognitive advantage of awe. The literature connecting awe and cognition is surveyed and used to develop a view that situates awe as a critical component in the cognitive success of the human species.

Toward a sociology of evolution in the Anthropocene-Shared intentionality and cooperation through understanding minds

Sociology has a long tradition of diagnosing contemporary societies, but little theoretical and empirical instruments for analyzing the long-term evolution of human coexistence. This goes hand in hand with a bias to disregard insights of evolutionary theory and research. The main argument here to develop is that a sociology of evolution should enter at the core of our discipline. This becomes even more important in the era of the Anthropocene as a new geo-chronological period of the planet's evolution that is characterized by substantial human influencing of planetary ecological mechanisms and could be found in earth sediments. If human intervention in the planet has reached such a scale that its future fate is no longer shaped mainly by natural cosmological laws, but by human intervention, then sociology has to broaden its temporal and substantive perspective; it should reflect more explicitly on the relationship between nature, culture, and technology. In what follows, we plead for giving evolutionary sociology, especially the long-term evolution of human coexistence between nature and culture, a greater place in sociology. To this end, we address three points. First, we ask why sociology is not concerned with the co-evolution of other creatures, but almost exclusively focused on the development and social change of humans over the short period of the last few centuries. Second, we argue that, with respect to the nature-culture relationship, sociology has essentially followed a questionable scientific division of labor, according to which the natural sciences deal with natural phenomena and sociology with sociocultural phenomena. Finally, we address the debate on the Anthropocene and distinguish between two ways of responding to the challenges it poses, namely with more technology or with more culture.

The emergence of group fitness

Whether and how selection can act on collectives rather than single entities has been a tumultuous issue in evolutionary biology for decades. Despite examples of multilevel selection, a simple framework is needed that makes explicit the constraints that lead to the emergence of a "group fitness function." We use evolutionary game theory to show that two constraints are sufficient for the emergence of a well-defined group fitness, which could even apply to multispecies groups. First, different parts of the group contribute to one another's growth via resources produced proportionally to the density of each resource producer (not the density of the population receiving benefits). Second, invading groups do not share these resources with resident groups. Jointly, these two constraints lead to the "entanglement" of invading individuals' outcomes such that individual fitness can no longer be defined and group fitness predicts evolutionary dynamics through the emergence of a higher level evolutionary individual. Group fitness is an emergent property, irreducible to the fitness of the group's parts and exhibiting downward causality on the parts. By formalizing group fitness as a model for evolutionary transitions in individuality, these results open up a broad class of models under the multilevel-selection framework.

The ergodicity solution of the cooperation puzzle

When two entities cooperate by sharing resources, one relinquishes something of value to the other. This apparent altruism is frequently observed in nature. Why? Classical treatments assume circumstances where combining resources creates an immediate benefit, e.g. through complementarity or thresholds. Here we ask whether cooperation is predictable without such circumstances. We study a model in which resources self-multiply with fluctuations, a null model of a range of phenomena from viral spread to financial investment. Two fundamental growth rates exist: the ensemble-average growth rate, achieved by the average resources of a large population; and the time-average growth rate, achieved by individual resources over a long time. As a consequence of non-ergodicity, the latter is lower than the former by a term which depends on fluctuation size. Repeated pooling and sharing of resources reduces the effective size of fluctuations and increases the time-average growth rate, which approaches the ensemble-average growth rate in the many-cooperator limit. Therefore, cooperation is advantageous in our model for the simple reason that those who do it grow faster than those who do not. We offer this as a candidate explanation for observed cooperation in rudimentary environments, and as a behavioural baseline for cooperation more generally. This article is part of the theme issue 'Emergent phenomena in complex physical and socio-technical systems: from cells to societies'.

The ergodicity solution of the cooperation puzzle

When two entities cooperate by sharing resources, one relinquishes something of value to the other. This apparent altruism is frequently observed in nature. Why? Classical treatments assume circumstances where combining resources creates an immediate benefit, e.g. through complementarity or thresholds. Here we ask whether cooperation is predictable without such circumstances. We study a model in which resources self-multiply with fluctuations, a null model of a range of phenomena from viral spread to financial investment. Two fundamental growth rates exist: the ensemble-average growth rate, achieved by the average resources of a large population; and the time-average growth rate, achieved by individual resources over a long time. As a consequence of non-ergodicity, the latter is lower than the former by a term which depends on fluctuation size. Repeated pooling and sharing of resources reduces the effective size of fluctuations and increases the time-average growth rate, which approaches the ensemble-average growth rate in the many-cooperator limit. Therefore, cooperation is advantageous in our model for the simple reason that those who do it grow faster than those who do not. We offer this as a candidate explanation for observed cooperation in rudimentary environments, and as a behavioural baseline for cooperation more generally. This article is part of the theme issue 'Emergent phenomena in complex physical and socio-technical systems: from cells to societies'.

Pierre Teilhard de Chardin: a visionary in controversy

Teilhard de Chardin developed an evolutionary vision of our planetary future, currently developing from a sphere of life, or biosphere towards a sphere of mind, or noosphere. As a visionary, Teilhard was not only on the brink of formulating the internet, but he also anticipated current academic efforts to understand globalization, as well as human, cultural and technological evolution. However, his ideas are sources of enduring controversies in both scientific and theological circles. Here I uncover some of the core reasons why his ways of thinking and writing are often problematic, and propose a way forward. This note aims to introduce Teilhard's central article about the noosphere (The Formation of the Noosphere, 1947), but can also be read as an independent introduction to Teilhard's system of thought. A detailed exegesis of Teilhard's article is available as a supplementary document.

Conformity and content-biased cultural transmission in the evolution of altruism

The evolution of altruism has been extensively modeled under the assumption of genetic transmission, whereas the dynamics under cultural transmission are less well understood. Previous research has shown that cultural transmission can facilitate the evolution of altruism by increasing 1) the probability of adopting the altruistic phenotype, and 2) assortment between altruists. We incorporate vertical and oblique transmission, which can be conformist or anti-conformist, into models of parental care, sibling altruism, and altruism between individuals that meet assortatively. If oblique transmission is conformist, it becomes easier for altruism to invade a population of non-altruists as the probability of vertical transmission increases. If oblique transmission is anti-conformist, decreasing vertical transmission facilitates invasion by altruism in the assortative meeting model, whereas in other models, there is a trade-off: greater vertical transmission produces greater assortment among genetically related altruists, but lowers the probability of adopting altruism via anti-conformity. Compared to conditions for invasion under genetic transmission, e.g., Hamilton's rule, we show that invasion can be easier with sufficiently strong anti-conformity, and in some models, with sufficiently high assortment even if oblique transmission is conformist. We also explore invasion by an allele A that increases individuals' content bias for altruism, in the absence of other forms of cultural transmission. If costs and benefits combine additively, A invades under previously known conditions. If costs and benefits combine multiplicatively, invasion by A and by altruism become more difficult than in the corresponding additive models.

The origin of cooperation

We construct an evolutionary model of a population consisting of two types of interacting individuals that reproduce under random environmental conditions. We show that not only does the evolutionarily dominant behavior maximize the number of offspring of each type, it also minimizes the correlation between the number of offspring of each type, driving it toward ^-1. We provide several examples that illustrate how correlation can be used to explain the evolution of cooperation.

Egoistic punishment outcompetes altruistic punishment in the spatial public goods game

The evolution of costly punishment is a puzzle due to cooperators’ second-order free-riding. Previous studies have proposed many solutions mainly focused on reducing the punishment cost or punishing second-order free riders directly or indirectly. We attempt to explain this confusion from the perspective of punishment motivation, which is why the punisher is willing to pay the cost. The answer is that the punisher is egoistic. Egoistic punishment aims to protect punishers’ own cooperative benefits shared by the defectors. In such case, egoistic punishers would pay a cost in punishing defectors and retrieve lost payoffs from defectors. Here, we examined the evolution and performance of egoistic punishment and compared it with typical altruistic punishment using classic peer-punishment and pool-punishment modes. Results showed egoistic punishment can evolve and effectively promote cooperation within a large parameter range, whether in a well-mixed or structured population, or through peer-punishment or pool-punishment modes. This result is also robust to different strategy-updating rules. The evolution under the pool-punishment mechanism is more complicated. The influence of parameters is counter-intuitive because of cycle dominance; namely, the cost is the key factor to control the level of cooperation and the fine determines the ratio of the punishers and cooperators. Compared with altruistic punishment, egoistic punishment can promote cooperation in a lower-fine and higher-cost area, especially in the pool punishment mode, and the egoistic punishers have stronger survivability. Egoistic punishers represent the natural fairness in a social system. Results revealed that focusing on individual equity can significantly promote collective cooperation. This study provides another explanation for the evolution of costly punishment.

Banking on cooperation: an evolutionary analysis of microfinance loan repayment behaviour

Microfinance is an economic development tool that provides loans to low-income borrowers to stimulate economic growth and reduce financial hardship. Lenders typically require joint liability, where multiple borrowers share the responsibility of repaying a group loan. We propose that this lending practice creates a cooperation dilemma similar to that faced by humans and other organisms in nature across many domains. This could offer a real-world test case for evolutionary theories of cooperation from the biological sciences. In turn, such theories could provide new insights into loan repayment behaviour. We first hypothesise how group loan repayment efficacy should be affected by mechanisms of assortment from the evolutionary literature on cooperation, i.e. common ancestry (kin selection), prior interaction (reciprocity), partner choice, similarity of tags, social learning, and ecology and demography. We then assess selected hypotheses by reviewing 41 studies from 32 countries on micro-borrowers' loan repayment, evaluating which characteristics of borrowers are associated with credit repayment behaviour. Surprisingly, we find that kinship is mostly negatively associated with repayment efficacy, but prior interaction and partner choice are both more positively associated. Our work highlights the scope of evolutionary theory to provide systematic insight into how humans respond to novel economic institutions and interventions.

Core design principles for nurturing organization-level selection

Dynamic relationships between individuals and groups have been a focus for evolutionary theorists and modelers for decades. Among evolutionists, selfish gene theory promotes reductionist approaches while multilevel selection theory encourages a context-sensitive approach that appreciates that individuals and groups can both matter. Among economists, a comparable contrast is found wherein the reductionist shareholder primacy theory most associated with Nobel laureate Milton Friedman is very different from the context-sensitive focus on managing common resources that Nobel laureate Elinor Ostrom pioneered. In this article, we examine whether the core design principles that Ostrom advanced can cultivate selection at supra-individual levels across different domains. We show that Ostrom’s design principles that were forged in the context of managing natural resources are associated with positive outcomes for human social groups across a variety of functional domains.

Clinical psychology is an applied evolutionary science

Historically there has been only a limited relationship between clinical psychology and evolutionary science. This article considers the status of that relationship in light of a modern multi-dimensional and multi-level extended evolutionary approach. Evolution can be purposive and even conscious, and evolutionary principles can give guidance and provide consilience to clinical psychology, especially as it focuses more on processes of change. The time seems ripe to view clinical psychology as an applied evolutionary science.

A Systematic Review of Associations Between Interoception, Vagal Tone, and Emotional Regulation: Potential Applications for Mental Health, Wellbeing, Psychological Flexibility, and Chronic Conditions

Background: Interoception and heart rate variability have been found to predict outcomes of mental health and well-being. However, these have usually been investigated independently of one another.

Objectives: This systematic review aimed to explore a key gap in the current literature, that being, identifying whether HRV and interoception predict emotional regulation outcomes and strategies.

Methods: The process of article retrieval and selection followed the PRISMA guidelines. Databases PsychINFO, Web of Science, PubMed, CINAHL, and MEDLINE were scanned for papers published. Preliminary inclusion and exclusion criteria were specified following the PICO framework, whilst the CHARMS framework was used to help formulate the research question, and critically assess for bias.

Results: Two hundred and thirty-seven studies were identified after initial database searches. Of these, eight studies were included in the final selection. Six studies explored the associations between HRV and ER, whilst three investigated the associations between interoception and ER (one study included both). Results show that greater HRV and interoception are associated with better ER. Specifically, high parasympathetic activity largely predicted the use of adaptive ER strategies such as reappraisal, and better acceptance of emotions. High interoception, instead, was predictive of effective downregulation of negative emotions and handling of social uncertainty, there was no association with any specific ER strategy.

Conclusions: Awareness of one's own bodily feelings and vagal activation seem to be of central importance for the effective regulation of emotional responses. However, one limitation is the small sample of studies found, thus more studies in this area are needed in the future.

Coexistence and cooperation in structured habitats

Background

Natural habitats are typically structured, imposing constraints on inhabiting populations and their interactions. Which conditions are important for coexistence of diverse communities, and how cooperative interaction stabilizes in such populations, have been important ecological and evolutionary questions.

Results

We investigate a minimal ecological framework of microbial population dynamics that exhibits crucial features to show coexistence: Populations repeatedly undergo cycles of separation into compartmentalized habitats and mixing with new resources. The characteristic time-scale is longer than that typical of individual growth. Using analytic approximations, averaging techniques and phase-plane methods of dynamical systems, we provide a framework for analyzing various types of microbial interactions. Population composition and population size are both dynamic variables of the model; they are found to be decoupled both in terms of time-scale and parameter dependence. We present specific results for two examples of cooperative interaction by public goods: collective antibiotics resistance, and enhanced iron-availability by pyoverdine. We find stable coexistence to be a likely outcome.

Conclusions

The two simple features of a long mixing time-scale and spatial compartmentalization are enough to enable coexisting strains. In particular, costly social traits are often stabilized in such an environment—and thus cooperation established.

The genetic and cultural evolution of unsustainability

Anthropogenic changes are accelerating and threaten the future of life on earth. While the proximate mechanisms of these anthropogenic changes are well studied (e.g., climate change, biodiversity loss, population growth), the evolutionary causality of these anthropogenic changes have been largely ignored. Anthroecological theory (AET) proposes that the ultimate cause of anthropogenic environmental change is multi-level selection for niche construction and ecosystem engineering. Here, we integrate this theory with Lotka's Maximum Power Principle and propose a model linking energy extraction from the environment with genetic, technological and cultural evolution to increase human ecosystem carrying capacity. Carrying capacity is partially determined by energetic factors such as the net energy a population can acquire from its environment and the efficiency of conversion from energy input to offspring output. These factors are under Darwinian genetic selection in all species, but in humans, they are also determined by technology and culture. If there is genetic or non-genetic heritable variation in the ability of an individual or social group to increase its carrying capacity, then we hypothesize that selection or cultural evolution will act to increase carrying capacity. Furthermore, if this evolution of carrying capacity occurs faster than the biotic components of the ecological system can respond via their own evolution, then we hypothesize that unsustainable ecological changes will result.

Replicator population dynamics of group interactions: Broken symmetry, thresholds for metastability, and macroscopic behavior

The effect of group structure on cooperative behavior is not well understood. In this paper, we study the dynamics of a public goods game involving n-agent interactions. In the proposed setup, the population is organized into groups. We associate the individual fitness to group performance, while the evolutionary dynamics takes place globally. We derive analytical expressions and show that the model exhibits several fixed points, including the symmetric homogeneous states of total cooperation and total defection, which are unstable and stable, respectively. Interestingly, even if both individual and group levels are organized as well-mixed populations, the dynamics displays intermediate values of cooperation under the replicator dynamics. Namely, as soon as one of the groups, at least, is fully cooperative, intermediary fixed points appear for the rest of the groups. In addition to the analytical approach, we have performed numerical simulations that reproduce the internal fixed points obtained theoretically, showing coexisting intermediate levels of cooperation. Potential implications of these results in terms of group selection and the role of social norms are also discussed.

The ecology of empire The dynamics of strategic differentiation-integration in two competing Western European biocultural groups

We tracked the relative integration and differentiation among life history traits over the period spanning AD 1800-1999 in the Britannic and Gallic biocultural groups. We found that Britannic populations tended toward greater strategic differentiation, while Gallic populations tended toward greater strategic integration. The dynamics of between-group competition between these two erstwhile rival biocultural groups were hypothesized as driving these processes. We constructed a latent factor that specifically sought to measure between-group competition and residualized it for the logarithmic effects of time. We found a significantly asymmetrical impact of between-group competition, where the between-group competition factor appeared to be driving the diachronic integration in Gallic populations but had no significantly corresponding influence on the parallel process of diachronic differentiation in Britannic populations. This suggests that the latter process was attributable to some alternative and unmeasured causes, such as the resource abundance consequent to territorial expansion rather than contraction.

Local interactions and self-organized spatial patterns stabilize microbial cross-feeding against cheaters

Mutualisms are ubiquitous, but models predict they should be susceptible to cheating. Resolving this paradox has become relevant to synthetic ecology: cooperative cross-feeding, a nutrient-exchange mutualism, has been proposed to stabilize microbial consortia. Previous attempts to understand how cross-feeders remain robust to non-producing cheaters have relied on complex behaviour (e.g. cheater punishment) or group selection. Using a stochastic spatial model, we demonstrate two novel mechanisms that can allow cross-feeders to outcompete cheaters, rather than just escape from them. Both mechanisms work through the spatial segregation of the resources, which prevents individual cheaters from acquiring the resources they need to reproduce. First, if microbe dispersal is low but resources are shared widely, then the cross-feeders self-organize into stable spatial patterns. Here the cross-feeders can build up where the resource they need is abundant, and send their resource to where their partner is, separating resources at regular intervals in space. Second, if dispersal is high but resource sharing is local, then random variation in population density creates small-scale variation in resource density, separating the resources from each other by chance. These results suggest that cross-feeding may be more robust than previously expected and offer strategies to engineer stable consortia.

How to Make Swarms Open-Ended? Evolving Collective Intelligence Through a Constricted Exploration of Adjacent Possibles

We propose an approach to open-ended evolution via the simulation of swarm dynamics. In nature, swarms possess remarkable properties, which allow many organisms, from swarming bacteria to ants and flocking birds, to form higher-order structures that enhance their behavior as a group. Swarm simulations highlight three important factors to create novelty and diversity: (a) communication generates combinatorial cooperative dynamics, (b) concurrency allows for separation of time scales, and (c) complexity and size increases push the system towards transitions in innovation. We illustrate these three components in a model computing the continuous evolution of a swarm of agents. The results, divided into three distinct applications, show how emergent structures are capable of filtering information through the bottleneck of their memory, to produce meaningful novelty and diversity within their simulated environment.

What Modern Sports Competitions Can Tell Us About Human Nature

To fully understand human behavior, it seems inevitable to approach it from an evolutionary perspective. However, much of human behavior has been overwritten by culture and society, thus allowing little insight into how it might have evolved amid natural and sexual selection. Here, I argue that sports competitions, although a cultural phenomenon in themselves, strip away many of the cultural layers and reveal more primary, rudimentary aspects of human behavior. Fortunately, because they are ubiquitous, meticulously recorded, and often quantified in great detail, sports competitions provide a plethora of usable data. In this article I provide an evolutionary account of the cross-cultural existence and popularity of sports by reviewing evidence of four functional hypotheses that regard the omnipresence of sports as a by-product of fitness-related adaptations (skill acquisition and development, status seeking, courtship display, and coalition formation). Then I outline how the growing body of sports data and documentation can be exploited for increasing our understanding of human nature (e.g., on conflict and cooperation, lateral preferences, territoriality, and nonverbal communication). The article concludes by giving guidelines for future cross-disciplinary research to advance the understanding of how evolution has shaped human behavior.

Disengaging from the ultrasocial economy: The challenge of directing evolutionary change

We appreciate the depth and breadth of comments we received. They reflect the interdisciplinary challenge of our inquiry and reassured us of its broad interest. We believe that our target article and the criticisms, elaborations, and extensions of the commentators can be an important contribution to establishing human ultrasociality as a new field of social science inquiry. A few of the commentators questioned our definition of ultrasociality, and we begin our response with an elaboration of that definition and a defense of our argument that human ultrasociality began with agriculture. We then respond to the second major area of controversy, namely, our use of group selection to explain the economic drivers behind the agricultural transition. We then focus on the issue of human intentionality raised by the phenomenon of collective intelligence. The intriguing question is to what extent can an entire culture change its own destiny? We then address the issue of the division of labor raised by a number of commentators. The complex division of labor was both a driver and a defining characteristic of ultrasociality, even though it was present in simpler forms in earlier societies. The remaining issues addressed include energy and complexity, expansion and sustainability, and the accelerating evolution of human ultrasociality. These were raised by only a few commentators, but their importance warrants further elaboration.

Shearing in flow environment promotes evolution of social behavior in microbial populations

How producers of public goods persist in microbial communities is a major question in evolutionary biology. Cooperation is evolutionarily unstable, since cheating strains can reproduce quicker and take over. Spatial structure has been shown to be a robust mechanism for the evolution of cooperation. Here we study how spatial assortment might emerge from native dynamics and show that fluid flow shear promotes cooperative behavior. Social structures arise naturally from our advection-diffusion-reaction model as self-reproducing Turing patterns. We computationally study the effects of fluid advection on these patterns as a mechanism to enable or enhance social behavior. Our central finding is that flow shear enables and promotes social behavior in microbes by increasing the group fragmentation rate and thereby limiting the spread of cheating strains. Regions of the flow domain with higher shear admit high cooperativity and large population density, whereas low shear regions are devoid of life due to opportunistic mutations.

According to the principle of the ‘survival of the fittest’, selfish individuals should be better off compared to peers that cooperate with each other. Indeed, even though a population of organisms benefits from working together, selfish members can exploit the cooperative behavior of others without doing their part. These ‘cheaters’ then use their advantage to reproduce faster and take over the population.

Yet, social cooperation is widespread in the natural world, and occurs in creatures as diverse as bacteria and whales. How can it arise and persist then? One idea is that when individuals form distinct groups, the ones with cheaters will perish. Even though a selfish individual will fare better than the rest of its team, overall, cooperating groups will survive more and reproduce faster; ultimately, they will be favored by evolution. This is called group selection.

Here, Uppal and Vural examine how the physical properties of the environment can influence the evolution of social interactions between bacteria. To this end, mathematical models are used to simulate how bacteria grow, evolve and drift in a flowing fluid. These are based on equations worked out from the behavior of real-life populations.

The results show that flow patterns in a fluid habitat govern the social behavior of bacteria. When different regions of the fluid are moving at different speeds, ‘shear forces’ are created that cause bacterial colonies to distort and occasionally break apart to form two groups. As such, cooperative groups will rapidly form new cooperating colonies, whereas groups with cheaters will reproduce slower or perish.

Furthermore, results show that when different areas of the fluid have different shear forces, social cooperation will only prevail in certain places. This makes it possible to use flow patterns to fine tune social evolution so that cooperating bacteria will be confined in a certain region. Outside of this area, these bacteria would be taken over by cheaters and go extinct.

Bacteria are both useful and dangerous to humans: for example, certain species can break down pollutants in the water, when others cause deadly infections. These results show it could be possible to control the activity of these microorganisms to our advantage by changing the flow of the fluids in which they live. More broadly, the simulations developed by Uppal and Vural can be applied to a variety of ecosystems where microscopic organisms inhabit fluids, such as plankton flowing in oceanic currents.

Dynamics of social behaviour at parturition in a gregarious ungulate

Group living is the behavioural response that results when individuals assess the costs vs benefits of sociality, and these trade-offs vary across an animal's life. Here we quantitatively assess how periparturient condition (mother/non-mother) and births affect the dynamics of social interactions of a gregarious ungulate, and how such can help to explain evolutionary hypotheses of the mother-offspring bond. To achieve this we used data of the individual movement of a group of Scottish blackface sheep (Ovis aries) marked with GPS collars and properties of mathematical graphs (networks). Euclidean pair-wise distance between sheep were threshold at different percentiles to determine network links, and these thresholds have a profound effect on the connectivity of the resulting network. Births increased the average pair-wise distance between mothers, and between mothers and non-mothers, with less effect on the distance between non-mothers. Mothers occupied peripheral positions within the flock, more evident following births. Associations between individuals (i.e. network community change) were highly dynamic, though mothers were less likely to change community than non-mothers, especially after births. Births hampered individual communication within the flock (assessed via network closeness centrality), especially in mothers. Overall leadership (lead positioning relative to flock movement) was not associated to reproductive condition, and individual leadership rank was not affected by births. A ten minute GPS acquisition time was adequate to capture complex social dynamics in sheep movement. The results on mother's isolation behaviour support the hypotheses of selection for maternal imprint facilitation, reducing risks to nursing alien offspring, and group/multilevel selection on group formation.

Applying a cultural multilevel selection framework to the adoption of sustainable management practices in California viticulture

In light of the ongoing environmental impacts of agriculture, understanding farmer adoption of sustainable management practices (SMPs) is an important priority. Relatively little work in agricultural adoption has explicitly examined the multilevel dynamics of adoption decision-making. Yet because many SMPs involve cooperative dilemmas-they are individually costly but provide group benefits-understanding the dynamics of both individual and group level behavioral change is critical. In this paper, we argue that cultural evolutionary theory is well suited to examining the emergence and spread of cooperative SMPs, and we illustrate this claim by applying a cultural multilevel selection (CMLS) framework to the adoption of SMPs on the part of winegrape growers in California, USA. Using survey data from over 800 winegrape growers in 3 regions, we estimate the individual-level costs and group-level benefits of 44 different SMPs. We then relate this to variation in their adoption within and between winegrape growing regions to characterize the scope for cultural group selection of the various practices. We also identify a number of mechanisms that might plausibly explain the observed patterns of variation, including various forms of cultural group selection. We highlight the added value of this perspective with respect to the established approaches and outline the data requirements for researchers to conduct similar studies in other settings. Our results underscore the potential for a cultural evolutionary perspective to shed light on the multiscale mechanisms driving adoption of SMPs and, more generally, the promise of cultural evolutionary approaches to supplement existing analytical toolkits in sustainability science.

Evolving the Anthropocene: linking multi-level selection with long-term social-ecological change

To what degree is cultural multi-level selection responsible for the rise of environmentally transformative human behaviors? And vice versa? From the clearing of vegetation using fire to the emergence of agriculture and beyond, human societies have increasingly sustained themselves through practices that enhance environmental productivity through ecosystem engineering. At the same time, human societies have increased in scale and complexity from mobile bands of hunter-gatherers to telecoupled world systems. We propose that these long-term changes are coupled through positive feedbacks among social and environmental changes, coevolved primarily through selection acting at the group level and above, and that this can be tested by combining archeological evidence with mechanistic experiments using an agent-based virtual laboratory (ABVL) approach. A more robust understanding of whether and how cultural multi-level selection couples human social change with environmental transformation may help in addressing the long-term sustainability challenges of the Anthropocene.