Diminishing returns in social evolution: the not-so-tragic commons

A challenge for evolutionary theory is to understand how cooperation can occur in the presence of competition and cheating, a problem known as the tragedy of commons. Here I examine how varying the fitness returns from reproductive competition or cooperation affects the negative impact of competition on a social group. Varying linear returns does not affect the impact of competition. However, diminishing returns, where additional investments in either competition or cooperation give smaller and smaller rewards, reduce the effects of competition on the group. I show that diminishing returns are common in many systems, including social vertebrates, microbes, social insects and mutualisms among species. This suggests that the tragedy of the commons is not so tragic and that the disruptive effects of competition upon social life will often be minor.     

野生动物肇事公众责任保险发展困境与优化路径

野生动物肇事公众责任保险自开展以来, 存在着保险实施效果较差、承保机构参与不积极、保险范围难以扩大等问题, 在有效缓解人兽矛盾方面表现欠佳, 阻碍了生物多样性保护的落实与执行。本文以现阶段实施该保险的云南、西藏、浙江、四川为例梳理其应用模式, 并对具体地区的保险模式进行比较分析。研究表明, 野生动物肇事公众责任保险陷入发展困境的主要原因是产品设计不科学、财政经费不充足、政策制度不健全和保险体系不完善。建议优化保险要素设计、扩展经费来源渠道、健全配套政策法规, 建立政府主导、多方参与的中央财政补贴野生动物肇事公众责任保险体系, 该保险体系对于解决人兽冲突、支持生物多样性的保护、建立地球生命共同体具有重要的价值与意义。     

Resettlement challenges and dilemmas: An in‐depth case study of Bhutanese refugee women in Australia

In this paper, the perceptions of Bhutanese refugee women were explored in relation to their changing identity and their behavioural responses in the use of preventive health services following resettlement. Interviews with 30 Bhutanese refugee women in Melbourne revealed resettlement drivers, challenges and dilemmas. There was no option for women other than resettlement, women wanted to escape from bad conditions and hopes for a better future for their children was critical in their thinking. Resettlement introduced new unexpected challenges including cultural discontinuity, changed dependency and a sense of not belonging. Dilemmas were apparent in their experiences including: despondency and contentment, gratitude and regret; and identifying as either Australian or refugee. Motherhood was important to women in this study and was challenged by changed dependency with their children in resettlement. Challenges of cultural discontinuity included the impact of communication difficulties and illiteracy and the absence of social connections with neighbours. A better understanding of how changing identities of women interact should lead to more effective strategies including tailored programs and activities.     

Cooperation in two-person evolutionary games with complex personality profiles

We propose a theory of evolution of social systems which generalizes the standard proportional fitness rule of the evolutionary game theory. The formalism is applied to describe the dynamics of two-person one-shot population games. In particular it predicts the non-zero level of cooperation in the long run for the Prisoner's Dilemma games, the increase of the fraction of cooperators for general classes of the Snow-Drift game, and stable nonzero cooperation level for coordination games.     

Evolution of contingent altruism when cooperation is expensive

The ubiquity of cooperation has motivated a major research program over the last 50 years to discover ever more minimal conditions for the evolution of altruism. One important line of work is based on favoritism toward those who appear to be close relatives. Another important line is based on continuing interactions, whether between individuals (e.g., reciprocity) or between lines of descent in a viscous population. Here, we use an agent-based model to demonstrate a new mechanism that combines both lines of work to show when and how favoritism toward apparently similar others can evolve in the first place. The mechanism is the joint operation of viscosity and of tags (heritable, observable, and initially arbitrary characteristics), which serve as weak and potentially deceptive indicators of relatedness. Although tags are insufficient to support cooperation alone, we show that this joint mechanism vastly increases the range of environments in which contingent altruism can evolve in viscous populations. Even though our model is quite simple, the subtle dynamics underlying our results are not tractable using formal analytic tools (such as analysis of evolutionarily stable strategies), but are amenable to agent-based simulation.     

A strategy to increase cooperation in the volunteer's dilemma: reducing vigilance improves alarm calls

One of the most common examples of cooperation in animal societies is giving the alarm in the presence of a predator. A reduction in individual vigilance against predators when group size increases (the "group size effect") is one of the most frequently reported relationships in the study of animal behavior, and is thought to be due to relaxed selection, either because more individuals can detect the predator more easily (the "many eyes" effect) or because the risk of predator attack is diluted on more individuals (the "selfish herd" effect). I show that these hypotheses are not theoretically grounded: because everybody relies on someone else to raise the alarm, the probability that at least one raises the alarm declines with group size; therefore increasing group size does not lead to relaxed selection. Game theory shows, instead, that increasing the risk that the predator is not reported (by reducing vigilance) induces everybody to give the alarm more often. The group size effect, therefore, can be due to strategic behavior to improve the production of a public good. This shows how a selfish behavior can lead to a benefit for the group, and suggests a way to solve social dilemmas in the absence of relatedness and repeated interactions.     

The evolution of payoff matrices: providing incentives to cooperate

Most of the work in evolutionary game theory starts with a model of a social situation that gives rise to a particular payoff matrix and analyses how behaviour evolves through natural selection. Here, we invert this approach and ask, given a model of how individuals behave, how the payoff matrix will evolve through natural selection. In particular, we ask whether a prisoner's dilemma game is stable against invasions by mutant genotypes that alter the payoffs. To answer this question, we develop a two-tiered framework with goal-oriented dynamics at the behavioural time scale and a diploid population genetic model at the evolutionary time scale. Our results are two-fold: first, we show that the prisoner's dilemma is subject to invasions by mutants that provide incentives for cooperation to their partners, and that the resulting game is a coordination game similar to the hawk-dove game. Second, we find that for a large class of mutants and symmetric games, a stable genetic polymorphism will exist in the locus determining the payoff matrix, resulting in a complex pattern of behavioural diversity in the population. Our results highlight the importance of considering the evolution of payoff matrices to understand the evolution of animal social systems.     

GROUP FORMATION AND THE EVOLUTION OF SOCIALITY

In spite of its intrinsic evolutionary instability, altruistic behavior in social groups is widespread in nature, spanning from organisms endowed with complex cognitive abilities to microbial populations. In this study, we show that if social individuals have an enhanced tendency to form groups and fitness increases with group cohesion, sociality can evolve and be maintained in the absence of actively assortative mechanisms such as kin recognition or nepotism toward other carriers of the social gene. When explicitly taken into account in a game‐theoretical framework, the process of group formation qualitatively changes the evolutionary dynamics with respect to games played in groups of constant size and equal grouping tendencies. The evolutionary consequences of the rules underpinning the group size distribution are discussed for a simple model of microbial aggregation by differential attachment, indicating a way to the evolution of sociality bereft of peer recognition.     

Evolutionary dynamics of the continuous iterated prisoner's dilemma

The iterated prisoner's dilemma (IPD) has been widely used in the biological and social sciences to model dyadic cooperation. While most of this work has focused on the discrete prisoner's dilemma, in which actors choose between cooperation and defection, there has been some analysis of the continuous IPD, in which actors can choose any level of cooperation from zero to one. Here, we analyse a model of the continuous IPD with a limited strategy set, and show that a generous strategy achieves the maximum possible payoff against its own type. While this strategy is stable in a neighborhood of the equilibrium point, the equilibrium point itself is always vulnerable to invasion by uncooperative strategies, and hence subject to eventual destabilization. The presence of noise or errors has no effect on this result. Instead, generosity is favored because of its role in increasing contributions to the most efficient level, rather than in counteracting the corrosiveness of noise. Computer simulation using a single-locus infinite alleles Gaussian mutation model suggest that outcomes ranging from a stable cooperative polymorphism to complete collapse of cooperation are possible depending on the magnitude of the mutational variance. Also, making the cost of helping a convex function of the amount of help provided makes it more difficult for cooperative strategies to invade a non-cooperative equilibrium, and for the cooperative equilibrium to resist destabilization by non-cooperative strategies. Finally, we demonstrate that a much greater degree of assortment is required to destabilize a non-cooperative equilibrium in the continuous IPD than in the discrete IPD. The continuous model outlined here suggests that incremental amounts of cooperation lead to rapid decay of cooperation and thus even a large degree of assortment will not be sufficient to allow cooperation to increase when cooperators are rare. The extreme degree of assortment required to destabilize the non-cooperative equilibrium, as well as the instability of the cooperative equilibrium, may help explain why cooperation in Prisoner's Dilemmas is so rare in nature.     

Cooperation and the evolution of intelligence

The high levels of intelligence seen in humans, other primates, certain cetaceans and birds remain a major puzzle for evolutionary biologists, anthropologists and psychologists. It has long been held that social interactions provide the selection pressures necessary for the evolution of advanced cognitive abilities (the 'social intelligence hypothesis'), and in recent years decision-making in the context of cooperative social interactions has been conjectured to be of particular importance. Here we use an artificial neural network model to show that selection for efficient decision-making in cooperative dilemmas can give rise to selection pressures for greater cognitive abilities, and that intelligent strategies can themselves select for greater intelligence, leading to a Machiavellian arms race. Our results provide mechanistic support for the social intelligence hypothesis, highlight the potential importance of cooperative behaviour in the evolution of intelligence and may help us to explain the distribution of cooperation with intelligence across taxa.