Conflicts of interest and the evolution of decision sharing

Social animals regularly face consensus decisions whereby they choose, collectively, between mutually exclusive actions. Such decisions often involve conflicts of interest between group members with respect to preferred action. Conflicts could, in principle, be resolved, either by sharing decisions between members (‘shared decisions’) or by one ‘dominant’ member making decisions on behalf of the whole group (‘unshared decisions’). Both, shared and unshared decisions, have been observed. However, it is unclear as to what favours the evolution of either decision type. Here, after a brief literature review, we present a novel method, involving a combination of self-organizing system and game theory modelling, of investigating the evolution of shared and unshared decisions. We apply the method to decisions on movement direction. We find that both, shared and unshared, decisions can evolve without individuals having a global overview of the group''s behaviour or any knowledge about other members'' preferences or intentions. Selection favours unshared over shared decisions when conflicts are high relative to grouping benefits, and vice versa. These results differ from those of group decision models relating to activity timings. We attribute this to fundamental differences between collective decisions about modalities that are disjunct (here, space) or continuous (here, time) with respect to costs/benefits.     

Community participation in health care decision making: is it feasible?

Health care reform strategies proposed by provincial governments include decentralized funding and increased public participation in decision making. These proposals do not give details as to the public participation process, and a number of questions have been raised by the experience of some communities. Which citizens should form the decision-making group? What information do they need? What kinds of decisions should they make? What level of participation should they have? The results of a survey by Abelson and associates (see pages 403 to 412 of this issue) challenge the assumption that "communities" are willing to participate in health-care and social-service decision making. Willingness varied according to the composition of the groups polled, and participants'' support for traditional decision makers increased after the complexities of the decision-making process were discussed. However, whereas their study measured willingness to participate at one point in time only, experience gained from Ontario''s Better Beginnings, Better Futures project indicates that, given sufficient time, "ordinary" citizens are willing and can acquire the skills needed to decide how resources should be allocated for social services.     

Impact of internal and external factors on prosocial choices in rhesus macaques

While traditional economic models assume that agents are self-interested, humans and most non-human primates are social species. Therefore, many of decisions they make require the integration of information about other social agents. This study asks to what extent information about social status and the social context in which decisions are taken impact on reward-guided decisions in rhesus macaques. We tested 12 monkeys of varying dominance status in several experimental versions of a two-choice task in which reward could be delivered to self only, only another monkey, both the self and another monkey, or neither. Results showed dominant animals were more prone to make prosocial choices than subordinates, but only when the decision was between a reward for self only and a reward for both self and other. If the choice was between a reward for self only and a reward for other only, no animal expressed altruistic behaviour. Finally, prosocial choices were true social decisions as they were strikingly reduced when the social partner was replaced by a non-social object. These results showed that as in humans, rhesus macaques'' social decisions are adaptive and modulated by social status and the cost associated with being prosocial.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.     

Where Next? Group Coordination and Collective Decision Making by Primates

Primate groups need to remain coordinated in their activities and collectively decide when and where to travel if they are to accrue the benefits and minimize the costs of sociality. The achievement of coordinated activity and group decision making therefore has important implications for individual survival and reproduction. The aim of this special issue is to bring together a collection of empirical, theoretical, and commentary articles by primatologists studying this rapidly expanding topic. In this article, we introduce the contributions within the special issue and provide a background to the topic. We begin by focusing on decisions that involve a collective transition between a resting and a moving state, a transition we term making the move. We examine whether specific predeparture behaviors seen during transitions represent intentional processes or more simple response facilitation. Next we classify decisions according to the contribution of individual group members, and describe how, and why, certain individuals can have a disproportionate influence over group-mates?? behavior. We then review how primate groups make decisions on the move. In particular, we focus on how variability in group size and spatial organization helps or hinders information transmission and coordination. We end with a discussion of new tools and methodology that will allow future investigators to address some outstanding questions in primate coordination and decision-making research. We conclude that a better integration of concepts and terminology, along with a focus on how individuals integrate environmental and social information, will be critical to developing a satisfactory understanding of collective patterns of behavior in primate systems.     

Democracy in animals: the evolution of shared group decisions

A 'consensus decision' is when the members of a group choose, collectively, between mutually exclusive actions. In humans, consensus decisions are often made democratically or in an 'equally shared' manner, i.e. all group members contribute to the decision. Biologists are only now realizing that shared consensus decisions also occur in social animals (other than eusocial insects). Sharing of decisions is, in principle, more profitable for groups than accepting the 'unshared' decision of a single dominant member. However, this is not true for all individual group members, posing a question as to how shared decision making could evolve. Here, we use a game theory model to show that sharing of decisions can evolve under a wide range of circumstances but especially in the following ones: when groups are heterogeneous in composition; when alternative decision outcomes differ in potential costs and these costs are large; when grouping benefits are marginal; or when groups are close to, or above, optimal size. Since these conditions are common in nature, it is easy to see how mechanisms for shared decision making could have arisen in a wide range of species, including early human ancestors.     

Evidence for social role in a dolphin social network

Social animals have to take into consideration the behaviour of conspecifics when making decisions to go by their daily lives. These decisions affect their fitness and there is therefore an evolutionary pressure to try making the right choices. In many instances individuals will make their own choices and the behaviour of the group will be a democratic integration of everyone’s decision. However, in some instances it can be advantageous to follow the choice of a few individuals in the group if they have more information regarding the situation that has arisen. Here I provide early evidence that decisions about shifts in activity states in a population of bottlenose dolphin follow such a decision-making process. This unshared consensus is mediated by a non-vocal signal, which can be communicated globally within the dolphin school. These signals are emitted by individuals that tend to have more information about the behaviour of potential competitors because of their position in the social network. I hypothesise that this decision-making process emerged from the social structure of the population and the need to maintain mixed-sex schools.     

Deciding group movements: Where and when to go

A group of animals can only move cohesively, if group members “somehow” reach a consensus about the timing (e.g., start) and the spatial direction/destination of the collective movement. Timing and spatial decisions usually differ with respect to the continuity of their cost/benefit distribution in such a way that, in principle, compromises are much more feasible in timing decision (e.g., median preferred time) than they are in spatial decisions. The consequence is that consensus costs connected to collective timing decisions are usually less skewed amongst group members than are consensus costs connected to spatial decisions. This, in turn, influences the evolution of decision sharing: sharing in timing decisions is most likely to evolve when conflicts are high relative to group cohesion benefits, while sharing in spatial decisions is most likely to evolve in the opposite situation. We discuss the implications of these differences for the study of collective movement decisions.     

Reproductive strategies and Islamic discourse: Malian migrants negotiate everyday life in Paris, France

Approximately 37 thousand Malians currently reside in France as part of the West African diaspora. Primarily Muslim, both women and men confront challenges to their understandings of Islamic prohibitions and expectations, especially those addressing conjugal relations and reproduction. Biomedical policies generate marital conflicts and pose health dilemmas for women who face family and community pressures to reproduce but biomedical encouragement to limit childbearing. For many women, contraception represents a reprieve from repeated pregnancies and fatigue in spite of resistance from those who contest women's reproductive decisions as antithetical to Islam. French social workers play a particularly controversial role by introducing women to a discourse of women's rights that questions the authority of husbands and of religious doctrine. Women and men frame decisions and debate in diverse interpretations of Islam as they seek to manage the contradictions of everyday life and assert individual agency in the context of immigration and health politics.     

Asymmetry within social groups: division of labour and intergroup competition

Social animals vary in their ability to compete with group members over shared resources and also vary in their cooperative efforts to produce these resources. Competition among groups can promote within‐group cooperation, but many existing models of intergroup cooperation do not explicitly account for observations that group members invest differentially in cooperation and that there are often within‐group competitive or power asymmetries. We present a game theoretic model of intergroup competition that investigates how such asymmetries affect within‐group cooperation. In this model, group members adopt one of two roles, with relative competitive efficiency and the number of individuals varying between roles. Players in each role make simultaneous, coevolving decisions. The model predicts that although intergroup competition increases cooperative contributions to group resources by both roles, contributions are predominantly from individuals in the less competitively efficient role, whereas individuals in the more competitively efficient role generally gain the larger share of these resources. When asymmetry in relative competitive efficiency is greater, a group's per capita cooperation (averaged across both roles) is higher, due to increased cooperation from the competitively inferior individuals. For extreme asymmetry in relative competitive efficiency, per capita cooperation is highest in groups with a single competitively superior individual and many competitively inferior individuals, because the latter acquiesce and invest in cooperation rather than within‐group competition. These predictions are consistent with observed features of many societies, such as monogynous Hymenoptera with many workers and caste dimorphism.     

A selective emotional decision-making bias elicited by facial expressions

Emotional and social information can sway otherwise rational decisions. For example, when participants decide between two faces that are probabilistically rewarded, they make biased choices that favor smiling relative to angry faces. This bias may arise because facial expressions evoke positive and negative emotional responses, which in turn may motivate social approach and avoidance. We tested a wide range of pictures that evoke emotions or convey social information, including animals, words, foods, a variety of scenes, and faces differing in trustworthiness or attractiveness, but we found only facial expressions biased decisions. Our results extend brain imaging and pharmacological findings, which suggest that a brain mechanism supporting social interaction may be involved. Facial expressions appear to exert special influence over this social interaction mechanism, one capable of biasing otherwise rational choices. These results illustrate that only specific types of emotional experiences can best sway our choices.     

Weaving carpets, weaving lives: Childhood and ethnicity in downtown Kathmandu

In the developing metropolis public perceptions about caste and ethnicity are influenced by historical trends in decisions about occupations; but what does this mean for children whose families decide they work? In Kathmandu's carpet industry, a large percentage of workers are Tamang, an ethnic group who represent a small percentage of the country's population. Organisations working with Tamang child labourers have predominantly used quantitative research data to construct their intervention strategies. This has left many factors unexamined. This paper discusses qualitative and quantitative research data generated by a team of Nepali practitioners striving to address child labour issues. The purpose of their study was to examine the social and cultural factors influencing child migration and the quality of life for children in the carpet industry. The methodology included participatory indicators of children's social, economic, physical and psychological well-being. The paper will draw on children's perspectives to highlight the role of ethnicity in opportunity and exploitation.     

Collective decision‐making and fission–fusion dynamics: a conceptual framework

Sociality exists in an extraordinary range of ecological settings. For individuals to accrue the benefits associated with social interactions, they are required to maintain a degree of spatial and temporal coordination in their activities, and make collective decisions. Such coordination and decision‐making has been the focus of much recent research. However, efforts largely have been directed toward understanding patterns of collective behaviour in relatively stable and cohesive groups. Less well understood is how fission–fusion dynamics mediate the process and outcome of collective decisions making. Here, we aim to apply established concepts and knowledge to highlight the implications of fission–fusion dynamics for collective decisions, presenting a conceptual framework based on the outcome of a small‐group discussion INCORE meeting (funded by the European Community's Sixth Framework Programme). First, we discuss how the degree of uncertainty in the environment shapes social flexibility and therefore the types of decisions individuals make in different social settings. Second, we propose that the quality of social relationships and the energetic needs of each individual influence fission decisions. Third, we explore how these factors affect the probability of individuals to fuse. Fourth, we discuss how group size and fission–fusion dynamics may affect communication processes between individuals at a local or global scale to reach a consensus or to fission. Finally, we offer a number of suggestions for future research, capturing emerging ideas and concepts on the interaction between collective decisions and fission–fusion dynamics.     

Follow the straggler: zebrafish use a simple heuristic for collective decision-making

Animal groups often make decisions sequentially, from the front to the back of the group. In such cases, individuals can use the choices made by earlier ranks, a form of social information, to inform their own choice. The optimal strategy for such decisions has been explored in models which differ on, for example, whether or not agents take into account the sequence of observed choices. The models demonstrate that choices made later in a sequence are more informative, but it is not clear if animals use this information or rely instead on simpler heuristics, such as quorum rules. We show that a simple rule ‘copy the last observed choice'', gives similar predictions to those of optimal models for most likely sequences. We trained groups of zebrafish to choose one arm of a Y-maze and used them to demonstrate various sequences to naive fish. We show that the naive fish appear to use a simple rule, most often copying the choice of the last demonstrator, which results in near-optimal choices at a fraction of the computational cost.     

Collective Learning and Optimal Consensus Decisions in Social Animal Groups

Learning has been studied extensively in the context of isolated individuals. However, many organisms are social and consequently make decisions both individually and as part of a collective. Reaching consensus necessarily means that a single option is chosen by the group, even when there are dissenting opinions. This decision-making process decouples the otherwise direct relationship between animals'' preferences and their experiences (the outcomes of decisions). Instead, because an individual''s learned preferences influence what others experience, and therefore learn about, collective decisions couple the learning processes between social organisms. This introduces a new, and previously unexplored, dynamical relationship between preference, action, experience and learning. Here we model collective learning within animal groups that make consensus decisions. We reveal how learning as part of a collective results in behavior that is fundamentally different from that learned in isolation, allowing grouping organisms to spontaneously (and indirectly) detect correlations between group members'' observations of environmental cues, adjust strategy as a function of changing group size (even if that group size is not known to the individual), and achieve a decision accuracy that is very close to that which is provably optimal, regardless of environmental contingencies. Because these properties make minimal cognitive demands on individuals, collective learning, and the capabilities it affords, may be widespread among group-living organisms. Our work emphasizes the importance and need for theoretical and experimental work that considers the mechanism and consequences of learning in a social context.     

Density, social information, and space use in the common lizard (Lacerta vivipara)

Socially acquired information is widespread in the animal kingdom.Many individuals make behavioral decisions based on such socialinformation. In particular, individuals may decide to leaveor select their habitat based on social information. Few studieshave investigated the role of density-related information, apotential social cue about habitat quality in dispersal. Here,we tested for the possibility that the phenotype of intrudercommon lizards (Lacerta vivipara) may inadvertently carry informationabout their natal population density. We found that such informationuse is likely. The behavior of focal lizard was influenced bythe natal population density of the intruder it was interactingwith. This suggests that individuals may use the behavior ofothers to acquire appropriate information about surroundingsand to base spatial decisions on this information. Density-relatedinformation may then affect individual movement decisions andthus metapopulation dynamics.     

When to use social information: the advantage of large group size in individual decision making

Correct decision making is crucial for animals to maximize foraging success and minimize predation risk. Group-living animals can make such decisions by using their own personal information or by pooling information with other group members (i.e. social information). Here, we investigate how individuals might best balance their use of personal and social information. We use a simple modelling approach in which individual decisions based upon social information are more likely to be correct when more individuals are involved and their personal information is more accurate. Our model predicts that when the personal information of group members is poor (accurate less than half the time), individuals should avoid pooling information. In contrast, when personal information is reliable (accurate at least half the time), individuals should use personal information less often and social information more often, and this effect should grow stronger in larger groups. One implication of this pattern is that social information allows less well-informed members of large groups to reach a correct decision with the same probability as more well-informed members of small groups. Thus, animals in larger groups may be able to minimize the costs of collecting personal information without impairing their ability to make correct decisions.     

The empirical question of thresholds and mechanisms of mate choice

Summary Theoretical discussions concerning how animals might best sample and select mates have suggested that individuals could base decisions either on a sample of mates (sampled-based decisions) or on a threshold of comparison (threshold-based decisions). Recent theoretical work demonstrates that threshold-based mating decisions generate higher expected fitness than sample-based mating decisions when search costs exist. Empirical results from most unmanipulated systems, however, either conclude that females make sample-based decisions or are inconclusive. A few experimental studies designed to detect mating thresholds purport to demonstrate threshold-based choice but an examination of these studies indicates such conclusions were premature. We believe that few examples of threshold-based choice exist because protocols designed to identify mating thresholds were often inconsistent with models of threshold choice. We suggest that future empirical work strive not to document mating thresholdsper se. Rather, future work might best reveal decision rules by manipulating the distribution of quality among potential mates; such manipulations predict uniquely how females using sample-based and threshold-based decision rules should behave.     

Composite collective decision-making

Individual animals are adept at making decisions and have cognitive abilities, such as memory, which allow them to hone their decisions. Social animals can also share information. This allows social animals to make adaptive group-level decisions. Both individual and collective decision-making systems also have drawbacks and limitations, and while both are well studied, the interaction between them is still poorly understood. Here, we study how individual and collective decision-making interact during ant foraging. We first gathered empirical data on memory-based foraging persistence in the ant Lasius niger. We used these data to create an agent-based model where ants may use social information (trail pheromones), private information (memories) or both to make foraging decisions. The combined use of social and private information by individuals results in greater efficiency at the group level than when either information source was used alone. The modelled ants couple consensus decision-making, allowing them to quickly exploit high-quality food sources, and combined decision-making, allowing different individuals to specialize in exploiting different resource patches. Such a composite collective decision-making system reaps the benefits of both its constituent parts. Exploiting such insights into composite collective decision-making may lead to improved decision-making algorithms.     

Identity economics and the brain: uncovering the mechanisms of social conflict

Social contexts can have dramatic effects on decisions. When individuals recognize each other as coming from the same social group, they can coordinate their actions towards a common goal. Conversely, information about group differences can lead to conflicts both economic and physical. Understanding how social information shapes decision processes is now a core goal both of behavioural economics and neuroeconomics. Here, we describe the foundations for research that combines the theoretical framework from identity economics with the experimental methods of neuroscience. Research at this intersection would fill important gaps in the literature not addressed by current approaches in either of these disciplines, nor within social neuroscience, psychology or other fields. We set forth a simple taxonomy of social contexts based on the information content they provide. And, we highlight the key questions that would be addressed by a new 'identity neuroeconomics'. Such research could serve as an important and novel link between the social and natural sciences.     

A simple threshold rule is sufficient to explain sophisticated collective decision-making

Decision-making animals can use slow-but-accurate strategies, such as making multiple comparisons, or opt for simpler, faster strategies to find a 'good enough' option. Social animals make collective decisions about many group behaviours including foraging and migration. The key to the collective choice lies with individual behaviour. We present a case study of a collective decision-making process (house-hunting ants, Temnothorax albipennis), in which a previously proposed decision strategy involved both quality-dependent hesitancy and direct comparisons of nests by scouts. An alternative possible decision strategy is that scouting ants use a very simple quality-dependent threshold rule to decide whether to recruit nest-mates to a new site or search for alternatives. We use analytical and simulation modelling to demonstrate that this simple rule is sufficient to explain empirical patterns from three studies of collective decision-making in ants, and can account parsimoniously for apparent comparison by individuals and apparent hesitancy (recruitment latency) effects, when available nests differ strongly in quality. This highlights the need to carefully design experiments to detect individual comparison. We present empirical data strongly suggesting that best-of-n comparison is not used by individual ants, although individual sequential comparisons are not ruled out. However, by using a simple threshold rule, decision-making groups are able to effectively compare options, without relying on any form of direct comparison of alternatives by individuals. This parsimonious mechanism could promote collective rationality in group decision-making.