Evolution of cooperation: cooperation defeats defection in the cornfield model

"Cooperation" defines any behavior that enhances the fitness of a group (e.g. a community or species), but which, by its nature, can be exploited by selfish individuals, meaning, firstly, that selfish individuals derive an advantage from exploitation which is greater than the average advantage that accrues to unselfish individuals. Secondly, exploitation has no intrinsic fitness value except in the presence of the "cooperative behavior". The mathematics is described by the simple Prisoner's Dilemma Game (PDG). It has previously been shown that koinophilia (the avoidance of sexual mates displaying unusual or atypical phenotypic features, such as mutations) stabilizes any inherited strategy in the simple or iterated PDG, meaning that it cannot be displaced by rare forms of alternative behavior which arise through mutation or occasional migration. In the present model equal numbers of cooperators and defectors (in the simple PDG) were randomly spread in a two-dimensional "cornfield" with uniformly distributed resources. Every individual was koinophilic, and interacted (sexually and in the PDG tournaments) only with individuals from within its immediate neighborhood. This model therefore tested whether cooperation can outcompete defection or selfishness in a straight, initially equally matched, evolutionary battle. The results show that in the absence of koinophilia cooperation was rapidly driven to extinction. With koinophilia there was a very rapid loss of cooperators in the first few generations, but thereafter cooperation slowly spread, ultimately eliminating defection completely. This result was critically dependent on sampling effects of neighborhoods. Small samples (resulting from low population densities or small neighborhood sizes) increase the probability that a chance neighborhood comes to consist predominantly of cooperators. A sexual preference for the most common phenotype in the neighborhood then makes that phenotype more common still. Once this occurs cooperation's spread becomes almost inevitable.     

Culture and the evolution of human cooperation

The scale of human cooperation is an evolutionary puzzle. All of the available evidence suggests that the societies of our Pliocene ancestors were like those of other social primates, and this means that human psychology has changed in ways that support larger, more cooperative societies that characterize modern humans. In this paper, we argue that cultural adaptation is a key factor in these changes. Over the last million years or so, people evolved the ability to learn from each other, creating the possibility of cumulative, cultural evolution. Rapid cultural adaptation also leads to persistent differences between local social groups, and then competition between groups leads to the spread of behaviours that enhance their competitive ability. Then, in such culturally evolved cooperative social environments, natural selection within groups favoured genes that gave rise to new, more pro-social motives. Moral systems enforced by systems of sanctions and rewards increased the reproductive success of individuals who functioned well in such environments, and this in turn led to the evolution of other regarding motives like empathy and social emotions like shame.     

How cooperation became the norm

Most of the contributions to Cooperation and Its Evolution grapple with the distinctive challenges presented by the project of explaining human sociality. Many of these puzzles have a ‘chicken and egg’ character: our virtually unparalleled capacity for large-scale cooperation is the product of psychological, behavioural, and demographic changes in our recent evolutionary history, and these changes are linked by complex patterns of reciprocal dependence. There is much we do not yet understand about the timing of these changes, and about the order in which different aspects of human social psychology (co-)evolved. In this review essay, I discuss four such puzzles the volume raises. These concern punishment and norm-psychology, moral judgement and the moral emotions, hierarchy and top-down coercion, and property rights and legal systems.     

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.     

When cooperation begets cooperation: the role of key individuals in galvanizing support

Life abounds with examples of conspecifics actively cooperating to a common end, despite conflicts of interest being expected concerning how much each individual should contribute. Mathematical models typically find that such conflict can be resolved by partial-response strategies, leading investors to contribute relatively equitably. Using a case study approach, we show that such model expectations can be contradicted in at least four disparate contexts: (i) bi-parental care; (ii) cooperative breeding; (iii) cooperative hunting; and (iv) human cooperation. We highlight that: (a) marked variation in contributions is commonplace; and (b) individuals can often respond positively rather than negatively to the contributions of others. Existing models have surprisingly limited power in explaining these phenomena. Here, we propose that, although among-individual variation in cooperative contributions will be influenced by differential costs and benefits, there is likely to be a strong genetic or epigenetic component. We then suggest that selection can maintain high investors (key individuals) when their contributions promote support by increasing the benefits and/or reducing the costs for others. Our intentions are to raise awareness in—and provide testable hypotheses of—two of the most poorly understood, yet integral, questions regarding cooperative ventures: why do individuals vary in their contributions and when does cooperation beget cooperation?     

Functional cooperation between the microtubule and actin cytoskeletons

In diverse cell types, microtubule (MT) and actin filament networks cooperate functionally during a wide variety of processes, including vesicle and organelle transport, cleavage furrow placement, directed cell migration, spindle rotation, and nuclear migration. The mechanisms by which MTs and actin filaments cooperate to mediate these different processes can be grouped into two broad categories: coordinated MT- and actin-based transport to move vesicles, organelles, and cell fate determinants; and targeting and capture of MT ends at cortical actin sites. Over the past several years, a growing number of cellular factors that bridge these cytoskeletal systems have been identified. These include 'hetero-motor' complexes (physically associated myosin and kinesin), myosin-CLIP170 complexes, formin homology (FH) proteins, dynein and the dynactin complex, Kar9p, coronin, Kelch repeat-containing proteins, and ERM proteins.     

Resource abundance and the critical transition to cooperation

Cooperation is abundant in nature, occurring at all levels of biological complexity. Yet cooperation is continually threatened by subversion from noncooperating cheaters. Previous studies have shown that cooperation can nevertheless be maintained when the benefits that cooperation provides to relatives outweigh the associated costs. These fitness costs and benefits are not fixed properties, but can be affected by the environment in which populations reside. Here, we describe how one environmental factor, resource abundance, decisively affects the evolution of cooperative public goods production in two independent evolving systems. In the Avida digital evolution platform, populations evolved in environments with different levels of a required resource, whereas populations of Vibrio cholerae evolved in the presence of different nutrient concentrations. In both systems, cooperators and cheaters co‐existed stably in resource‐rich environments, whereas cheaters dominated in resource‐poor environments. These two outcomes were separated by a sharp transition that occurred at a critical level of resource. These results offer new insights into how the environment affects the evolution of cooperation and highlight the challenges that populations of cooperators face when they experience environmental change.     

Within-host parasite cooperation and the evolution of virulence

Infections by multiple genotypes are common in nature and are known to select for higher levels of virulence for some parasites. When parasites produce public goods (PGs) within the host, such co-infections have been predicted to select for lower levels of virulence. However, this prediction is based on simplifying assumptions regarding epidemiological feedbacks on the multiplicity of infections (MOI). Here, we analyse the case of parasites producing a PG (for example, siderophore-producing bacteria) using a nested model that ties together within-host and epidemiological processes. We find that the prediction that co-infection should select for less virulent strains for PG-producing parasites is only valid if both parasite transmission and virulence are linear functions of parasite density. If there is a trade-off relationship such that virulence increases more rapidly than transmission, or if virulence also depends on the total amount of PGs produced, then more complex relationships between virulence and the MOI are predicted. Our results reveal that explicitly taking into account the distribution of parasite strains among hosts could help better understand the selective pressures faced by parasites at the population level.     

Evolution,epigenetics and cooperation

Explanations for biological evolution in terms of changes in gene frequencies refer to outcomes rather than process. Integrating epigenetic studies with older evolutionary theories has drawn attention to the ways in which evolution occurs. Adaptation at the level of the gene is giving way to adaptation at the level of the organism and higher-order assemblages of organisms. These ideas impact on the theories of how cooperation might have evolved. Two of the theories, i.e. that cooperating individuals are genetically related or that they cooperate for self-interested reasons, have been accepted for a long time. The idea that adaptation takes place at the level of groups is much more controversial. However, bringing together studies of development with those of evolution is taking away much of the heat in the debate about the evolution of group behaviour.     

Shame and honour drive cooperation

Can the threat of being shamed or the prospect of being honoured lead to greater cooperation? We test this hypothesis with anonymous six-player public goods experiments, an experimental paradigm used to investigate problems related to overusing common resources. We instructed the players that the two individuals who were least generous after 10 rounds would be exposed to the group. As the natural antithesis, we also test the effects of honour by revealing the identities of the two players who were most generous. The non-monetary, reputational effects induced by shame and honour each led to approximately 50 per cent higher donations to the public good when compared with the control, demonstrating that both shame and honour can drive cooperation and can help alleviate the tragedy of the commons.     

Between-group competition and human cooperation

A distinctive feature of human behaviour is the widespread occurrence of cooperation among unrelated individuals. Explaining the maintenance of costly within-group cooperation is a challenge because the incentive to free ride on the efforts of other group members is expected to lead to decay of cooperation. However, the costs of cooperation can be diminished or overcome when there is competition at a higher level of organizational hierarchy. Here we show that competition between groups resolves the paradigmatic 'public goods' social dilemma and increases within-group cooperation and overall productivity. Further, group competition intensifies the moral emotions of anger and guilt associated with violations of the cooperative norm. The results suggest an important role for group conflict in the evolution of human cooperation and moral emotions.     

Costly signaling and cooperation.

We propose an explanation of cooperation among unrelated members of a social group in which cooperation evolves because it constitutes an honest signal of the member's quality as a mate, coalition partner or competitor, and therefore results in advantageous alliances for those signaling in this manner. Our model is framed as a multi-player public goods game that involves no repeated or assortative interactions, so that non-cooperation would be a dominant strategy if there were no signaling benefits. We show that honest signaling of underlying quality by providing a public good to group members can be evolutionarily stable, and can proliferate in a population in which it is initially rare, provided that certain plausible conditions hold, including a link between group-beneficial signaling and underlying qualities of the signaler that would be of benefit to a potential mate or alliance partner. Our model applies to a range of cooperative interactions, including unconditionally sharing individually consumable resources, participating in group raiding or defense, and punishing free-riding or other violations of social norms.