Abstract
BackgroundThe origin and stability of cooperation is a hot topic in social and behavioural sciences. A complicated conundrum exists as defectors have an advantage over cooperators, whenever cooperation is costly so consequently, not cooperating pays off. In addition, the discovery that humans and some animal populations, such as lions, are polymorphic, where cooperators and defectors stably live together -- while defectors are not being punished--, is even more puzzling. Here we offer a novel explanation based on a Threshold Public Good Game (PGG) that includes the interaction of individual and group level selection, where individuals can contribute to multiple collective actions, in our model group hunting and group defense.ResultsOur results show that there are polymorphic equilibria in Threshold PGGs; that multi-level selection does not select for the most cooperators per group but selects those close to the optimum number of cooperators (in terms of the Threshold PGG). In particular for medium cost values division of labour evolves within the group with regard to the two types of cooperative actions (hunting vs. defense). Moreover we show evidence that spatial population structure promotes cooperation in multiple PGGs. We also demonstrate that these results apply for a wide range of non-linear benefit function types.ConclusionsWe demonstrate that cooperation can be stable in Threshold PGG, even when the proportion of so called free riders is high in the population. A fundamentally new mechanism is proposed how laggards, individuals that have a high tendency to defect during one specific group action can actually contribute to the fitness of the group, by playing part in an optimal resource allocation in Threshold Public Good Games. In general, our results show that acknowledging a multilevel selection process will open up novel explanations for collective actions.
Highlights
The origin and stability of cooperation is a hot topic in social and behavioural sciences
Effect of different threshold functions First we study the effect of the benefit function shape on the level of cooperation in the population (Figure 2) by means of individual based model (IBM) simulations
Here we show that multilevel selection in threshold Public Good Game (PGG) can maintain stable levels of polymorphism without the need of punishment or spatially explicit population structure
Summary
The origin and stability of cooperation is a hot topic in social and behavioural sciences. Selfish ‘defectors’ interacting with their own kind have a lower ‘payoff’ than cooperators, defectors would eventually totally replace cooperators in the population [8] A these explanations can be applied perfectly here as for example lion and human populations are neither completely well-mixed, nor spatially explicit in a sense as sedentary organisms, and punishment is not common in these instances. In most of the cases this is available for everyone, that is the common good is non-monopolizable (or nonexcludable, non-exclusive) and non-rival (synonym of joint in supply, non-diminishable) [32,33,34,35] This raises a collective action problem, where non cooperators, often termed as free riders, can reap the benefit of the common good without investing into it [24,34,35]
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