Synergy and discounting of cooperation in social dilemmas

The emergence and maintenance of cooperation by natural selection is an enduring conundrum in evolutionary biology, which has been studied using a variety of game theoretical models inspired by different biological situations. The most widely studied games are the Prisoner's Dilemma, the Snowdrift game and by-product mutualism for pairwise interactions, as well as Public Goods games in larger groups of interacting individuals. Here, we present a general framework for cooperation in social dilemmas in which all the traditional scenarios can be recovered as special cases. In social dilemmas, cooperators provide a benefit to the group at some cost, while defectors exploit the group by reaping the benefits without bearing the costs of cooperation. Using the concepts of discounting and synergy for describing how benefits accumulate when more than one cooperator is present in a group of interacting individuals, we recover the four basic scenarios of evolutionary dynamics given by (i) dominating defection, (ii) coexistence of defectors and cooperators, (iii) dominating cooperation and (iv) bi-stability, in which cooperators and defectors cannot invade each other. Generically, for groups of three or more interacting individuals further, more complex, dynamics can occur. Our framework provides the first unifying approach to model cooperation in different kinds of social dilemmas.     

The evolution of function-valued traits for conditional cooperation

In this paper we study the evolution of function-valued traits for cooperation in environments that display varying degrees of population viscosity. Traits measure an individual's intrinsic propensity to cooperate in a standard bilateral Prisoner's dilemma and can be increasing, decreasing or constant functions of the probability to interact with individuals of ones own genotype. We first analyse adaptation to homogenous environments (with constant degree of viscosity). Comparing environments characterized by different degrees of viscosity, we find that the relation between viscosity and the equilibrium type distribution is not monotone. In fact, it is possible that in fluid populations (no viscosity) there is more cooperation in equilibrium than in populations with intermediate degrees of viscosity. In a second step we analyse heterogenous environments (with varying degrees of viscosity). We find that under very weak assumptions on the distribution of the viscosity parameter strictly increasing functions are always selected and under some parameter constellations they are uniquely so.     

Life history strategy and human cooperation in economic games

Across five studies using samples from both Japan and United States (N = 2345), we take a multi-method approach to test the prediction from life history theory that a slow, compared to fast, life history strategy promotes investment in cooperative relationships. Studies 1 and 2 examined how different measures as proxies for life history strategy (i.e., Mini-K and High-K Strategy Scale) relate to cooperation in various economic games. Studies 3 to 5 measured early childhood environments (i.e., childhood harshness and unpredictability), manipulated resource scarcity using previously validated methods, and then measured cooperation. Across our studies, we also examined four hypothesized psychological mechanisms that could explain the relation between life history strategy and cooperation: temporal discounting, concern for reputation, social value orientation, and trust in others. Overall, we found no support for the hypothesis that life history strategy predicts cooperation or that early childhood environments interact with current resource scarcity to predict cooperation. Thus, our initial findings imply that life history theory may not account for individual variation in cooperation with unknown others.     

Know when to walk away: contingent movement and the evolution of cooperation

Models of the evolution of cooperation suggest that an important characteristic of successful strategies is the ability to respond contingently to the social environment. A number of mechanisms by which this can be accomplished have been suggested, some of which require relatively complex information processing systems. This research explores relaxing the requirements on information processing while preserving the evolvability of a cooperative strategy. The agent-based computer simulations reported here show that 'Walk Away,' a behavioral rule of extremely limited complexity (move after partner defects), can outperform more complex strategies under a number of conditions. Previous simulations of exit strategies have not examined the effect of implicit and explicit movement costs, different error rates, or the simultaneous presence of TFT and PAVLOV. The simulations reported here establish that the Walk Away strategy resists invasion and can invade a population of defectors at a lower initial frequency than any other strategy. The Walk Away strategy was successful, despite its simplicity, because it exploited aspects of the physical and social environment.     

Runaway selection for cooperation and strict-and-severe punishment

Punishing defectors is an important means of stabilizing cooperation. When levels of cooperation and punishment are continuous, individuals must employ suitable social standards for defining defectors and for determining punishment levels. Here we investigate the evolution of a social reaction norm, or psychological response function, for determining the punishment level meted out by individuals in dependence on the cooperation level exhibited by their neighbors in a lattice-structured population. We find that (1) cooperation and punishment can undergo runaway selection, with evolution towards enhanced cooperation and an ever more demanding punishment reaction norm mutually reinforcing each other; (2) this mechanism works best when punishment is strict, so that ambiguities in defining defectors are small; (3) when the strictness of punishment can adapt jointly with the threshold and severity of punishment, evolution favors the strict-and-severe punishment of individuals who offer slightly less than average cooperation levels; (4) strict-and-severe punishment naturally evolves and leads to much enhanced cooperation when cooperation without punishment would be weak and neither cooperation nor punishment are too costly; and (5) such evolutionary dynamics enable the bootstrapping of cooperation and punishment, through which defectors who never punish gradually and steadily evolve into cooperators who punish those they define as defectors.     

Revisiting “The Evolution of Reciprocity in Sizable Groups”: Continuous reciprocity in the repeated n-person prisoner's dilemma

For many years in evolutionary science, the consensus view has been that while reciprocal altruism can evolve in dyadic interactions, it is unlikely to evolve in sizable groups. This view had been based on studies which have assumed cooperation to be discrete rather than continuous (i.e., individuals can either fully cooperate or else fully defect, but they cannot continuously vary their level of cooperation). In real world cooperation, however, cooperation is often continuous. In this paper, we re-examine the evolution of reciprocity in sizable groups by presenting a model of the n-person prisoner's dilemma that assumes continuous rather than discrete cooperation. This model shows that continuous reciprocity has a dramatically wider basin of attraction than discrete reciprocity, and that this basin's size increases with efficiency of cooperation (marginal per capita return). Further, we find that assortative interaction interacts synergistically with continuous reciprocity to a much greater extent than it does with discrete reciprocity. These results suggest that previous models may have underestimated reciprocity's adaptiveness in groups. However, we also find that the invasion of continuous reciprocators into a population of unconditional defectors becomes realistic only within a narrow parameter space in which the efficiency of cooperation is close to its maximum bound. Therefore our model suggests that continuous reciprocity can evolve in large groups more easily than discrete reciprocity only under unusual circumstances.     

Language and cooperation in hominin scavenging

Bickerton (2009, 2014) hypothesizes that language emerged as the solution to a scavenging problem faced by proto-humans. We design a virtual world to explore how people use words to persuade others to work together for a common end. By gradually reducing the vocabularies that the participants can use, we trace the process of solving the hominin scavenging problem. Our experiment changes the way we think about social dilemmas. Instead of asking how does a group overcome the self-interest of its constituents, the question becomes, how do constituents persuade one another to work together for a common end that yields a common benefit?     

Cognitive cooperation

Cooperation can evolve in the context of cognitive activities such as perception, attention, memory, and decision making, in addition to physical activities such as hunting, gathering, warfare, and childcare. The social insects are well known to cooperate on both physical and cognitive tasks, but the idea of cognitive cooperation in humans has not received widespread attention or systematic study. The traditional psychological literature often gives the impression that groups are dysfunctional cognitive units, while evolutionary psychologists have so far studied cognition primarily at the individual level. We present two experiments that demonstrate the superiority of thinking in groups, but only for tasks that are sufficiently challenging to exceed the capacity of individuals. One of the experiments is in a brain-storming format, where advantages of real groups over nominal groups have been notoriously difficult to demonstrate. Cognitive cooperation might often operate beneath conscious awareness and take place without the need for overt training, as evolutionary psychologists have stressed for individual-level cognitive adaptations. In general, cognitive cooperation should be a central subject in human evolutionary psychology, as it already is in the study of the social insects. David Sloan Wilson is an evolutionary biologist interested in a broad range of issues relevant to human behavior. He has published in psychology, anthropology, and philosophy journals in addition to his mainstream biological research. He is author of Darwin’s Cathedral: Evolution, Religion, and the Nature of Society (University of Chicago Press, 2002) and co-author with philosopher Elliott Sober of Unto Others: The Evolution and Psychology of Unselfish Behavior (Harvard University Press, 1998). John J. Timmel received his Ph.D. from Binghamton University in 2001. Ralph R. Miller is Distinguished Professor of Psychology at Binghamton University. His research interests include information processing in animals, with an emphasis on elementary, evolutionarily derived, fundamentals of learning and memory that might be expected to generalize across species, including humans.     

Co-evolution of the archaeal tRNA-dependent amidotransferase GatCAB with tRNA(Asn)

The important identity elements in tRNA(Gln) and tRNA(Asn) for bacterial GatCAB and in tRNA(Gln) for archaeal GatDE are the D-loop and the first base pair of the acceptor stem. Here we show that Methanothermobacter thermautotrophicus GatCAB, the archaeal enzyme, is different as it discriminates Asp-tRNA(Asp) and Asp-tRNA(Asn) by use of U49, the D-loop and to a lesser extent the variable loop. Since archaea possess the tRNA(Gln)-specific amidotransferase GatDE, the archaeal GatCAB enzyme evolved to recognize different elements in tRNA(Asn) than those recognized by GatDE or by the bacterial GatCAB enzyme in their tRNA substrates.     

Wild justice and fair play: cooperation,forgiveness, and morality in animals

In this paper I argue that we can learn much about ‘wild justice’ and the evolutionary origins of social morality – behaving fairly – by studying social play behavior in group-living animals, and that interdisciplinary cooperation will help immensely. In our efforts to learn more about the evolution of morality we need to broaden our comparative research to include animals other than non-human primates. If one is a good Darwinian, it is premature to claim that only humans can be empathic and moral beings. By asking the question ‘What is it like to be another animal?’ we can discover rules of engagement that guide animals in their social encounters. When I study dogs, for example, I try to be a ‘dogocentrist’ and practice ‘dogomorphism.’ My major arguments center on the following ‘big’ questions: Can animals be moral beings or do they merely act as if they are? What are the evolutionary roots of cooperation, fairness, trust, forgiveness, and morality? What do animals do when they engage in social play? How do animals negotiate agreements to cooperate, to forgive, to behave fairly, to develop trust? Can animals forgive? Why cooperate and play fairly? Why did play evolve as it has? Does ‘being fair’ mean being more fit – do individual variations in play influence an individual's reproductive fitness, are more virtuous individuals more fit than less virtuous individuals? What is the taxonomic distribution of cognitive skills and emotional capacities necessary for individuals to be able to behave fairly, to empathize, to behave morally? Can we use information about moral behavior in animals to help us understand ourselves? I conclude that there is strong selection for cooperative fair play in which individuals establish and maintain a social contract to play because there are mutual benefits when individuals adopt this strategy and group stability may be also be fostered. Numerous mechanisms have evolved to facilitate the initiation and maintenance of social play to keep others engaged, so that agreeing to play fairly and the resulting benefits of doing so can be readily achieved. I also claim that the ability to make accurate predictions about what an individual is likely to do in a given social situation is a useful litmus test for explaining what might be happening in an individual's brain during social encounters, and that intentional or representational explanations are often important for making these predictions.     

It takes grouping and cooperation to get sociality

Cooperation and grouping are regularly studied as separate traits. The evolution of sociality however requires both that individuals get together in groups and that they cooperate within them. Because the level of cooperation can influence selection for group size, and vice versa, it is worth studying how these traits coevolve. Using a generally applicable two-trait optimization approach, we provide analytical solutions for three specific models. These solutions describe how cooperative associations of non-relatives evolve, and predict how large and how cooperative they will be. The analytical solutions help understand how changes in parameter values, such as the group carrying capacity and the costs of cooperation, affect group size and the level of cooperation in equilibrium. Although the analytical model makes a few simplifying assumptions—populations are assumed to be monomorphic for grouping as well as for cooperative tendencies, and group size is assumed to be deterministic—simulations show that its predictions are matched quite closely by results for settings where these assumptions do not hold.     

Kinetic mechanisms for overexpression insensitivity and oncogene cooperation

Minor (5-10 fold) activation of mitogenic signalling cascades typically induces cell division upon extracellular stimulation and is sufficient to support tumourigenesis when permanently triggered by activating mutations. Surprisingly, even strong signalling protein overexpression usually does not trigger deregulated cell proliferation, suggesting that basal state signalling is insensitive to wildtype protein overexpression. Using kinetic modelling of the core Ras cycle, we show that basal RasGTP signalling can be insensitive to Ras overexpression and thus identify a possible tumour suppression mechanism. We further show how phenotypically silent overexpression events within signalling cascades cooperate to bring about carcinogenesis. Our analyses underscore the need for a systems level understanding of tumour formation.     

Co-evolution and exploitation of host cell signaling pathways by bacterial pathogens

Bacterial pathogens have evolved by combinations of gene acquisition, deletion, and modification, which increases their fitness. Additionally, bacteria are able to evolve in quantum leaps via the ability to promiscuously acquire new genes. Many bacterial pathogens - especially Gram-negative enteric pathogens - have evolved mechanisms by which to subvert signal transduction pathways of eukaryotic cells by expressing genes that mimic or regulate host protein factors involved in a variety of signaling cascades. This results in the ability to cause diseases ranging from tumor formation in plants to gastroenteritis and bubonic plague. Here, we present recent advances on mechanisms of bacterial pathogen evolution, including specific signaling cascades targeted by their virulence genes with an emphasis on the ubiquitin modification system, Rho GTPase regulators, cytoskeletal modulators, and host innate immunity. We also comment briefly on evolution of host defense mechanisms in place that limit disease caused by bacterial pathogens.     

Spatial invasion of cooperation

The evolutionary puzzle of cooperation describes situations where cooperators provide a fitness benefit to other individuals at some cost to themselves. Under Darwinian selection, the evolution of cooperation is a conundrum, whereas non-cooperation (or defection) is not. In the absence of supporting mechanisms, cooperators perform poorly and decrease in abundance. Evolutionary game theory provides a powerful mathematical framework to address the problem of cooperation using the prisoner's dilemma. One well-studied possibility to maintain cooperation is to consider structured populations, where each individual interacts only with a limited subset of the population. This enables cooperators to form clusters such that they are more likely to interact with other cooperators instead of being exploited by defectors. Here we present a detailed analysis of how a few cooperators invade and expand in a world of defectors. If the invasion succeeds, the expansion process takes place in two stages: first, cooperators and defectors quickly establish a local equilibrium and then they uniformly expand in space. The second stage provides good estimates for the global equilibrium frequencies of cooperators and defectors. Under hospitable conditions, cooperators typically form a single, ever growing cluster interspersed with specks of defectors, whereas under more hostile conditions, cooperators form isolated, compact clusters that minimize exploitation by defectors. We provide the first quantitative assessment of the way cooperators arrange in space during invasion and find that the macroscopic properties and the emerging spatial patterns reveal information about the characteristics of the underlying microscopic interactions.     

Memory versus spatial disorder in the support of cooperation

In the conventional spatial formulation of the iterated prisoner’s dilemma only the results generated in the last round are taken into account in deciding the next choice. Historic memory can be implemented by featuring players with a summary of their previous winnings and moves. The effect of memory as a mechanism of supporting cooperation versus spatial disorder is assessed when the players are allowed for continuous degree of cooperation, not the mere binary cooperation/defection disjunctive.     

Ecological public goods games: cooperation and bifurcation

The Public Goods Game is one of the most popular models for studying the origin and maintenance of cooperation. In its simplest form, this evolutionary game has two regimes: defection goes to fixation if the multiplication factor r is smaller than the interaction group size N, whereas cooperation goes to fixation if the multiplication factor r is larger than the interaction group size N. Hauert et al. [Hauert, C., Holmes, M., Doebeli, M., 2006a. Evolutionary games and population dynamics: Maintenance of cooperation in public goods games. Proc. R. Soc. Lond. B 273, 2565-2570] have introduced the Ecological Public Goods Game by viewing the payoffs from the evolutionary game as birth rates in a population dynamic model. This results in a feedback between ecological and evolutionary dynamics: if defectors are prevalent, birth rates are low and population densities decline, which leads to smaller interaction groups for the Public Goods game, and hence to dominance of cooperators, with a concomitant increase in birth rates and population densities. This feedback can lead to stable co-existence between cooperators and defectors. Here we provide a detailed analysis of the dynamics of the Ecological Public Goods Game, showing that the model exhibits various types of bifurcations, including supercritical Hopf bifurcations, which result in stable limit cycles, and hence in oscillatory co-existence of cooperators and defectors. These results show that including population dynamics in evolutionary games can have important consequences for the evolutionary dynamics of cooperation.     

Friendship, cliquishness, and the emergence of cooperation

The evolution of cooperation is a central problem in biology and the social sciences. While theoretical work using the iterated prisoner's dilemma (IPD) has shown that cooperation among non-kin can be sustained among reciprocal strategies (i.e. tit-for-tat), these results are sensitive to errors in strategy execution, cyclical invasions by free riders, and the specific ecology of strategies. Moreover, the IPD assumes that a strategy's probability of playing the PD game with other individuals is independent of the decisions made by others. Here, we remove the assumption of independent pairing by studying a more plausible cooperative dilemma in which players can preferentially interact with a limited set of known partners and also deploy longer-term accounting strategies that can counteract the effects of random errors. We show that cooperative strategies readily emerge and persist in a range of noisy environments, with successful cooperative strategies (henceforth, cliquers) maintaining medium-term memories for partners and low thresholds for acceptable cooperation (i.e. forgiveness). The success of these strategies relies on their cliquishness-a propensity to defect with strangers if they already have an adequate number of partners. Notably, this combination of medium-term accounting, forgiveness, and cliquishness fits with empirical studies of friendship and other long-term relationships among humans.     

Mechanisms underlying long- and short-range nodal signaling in Zebrafish

Precise regulation of the signaling range of secreted molecules is essential for proper pattern formation during development. The Nodal family of TGF-beta proteins has been shown to function as both short- and long-range signals. But the underlying mechanisms remain elusive. In this study, we investigated the regulation of the signaling range of zebrafish Nodal proteins Cyclops and Squint, which are short- and long-range signals, respectively. We show that (1) the stability of Cyclops and Squint correlates with the activity range but increasing the stability of the short-range Cyclops does not increase its signaling range; (2) structural differences in the N-terminus region of the mature peptides of Cyclops and Squint determine their differences in the signaling range and swapping the N-terminus region of the Squint mature ligand into that of Cyclops makes the latter function at a distance.