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The evolution of prompt reaction to adverse ties.

Van Segbroeck S, Santos FC, Nowé A, Pacheco JM, Lenaerts T - BMC Evol. Biol. (2008)

Bottom Line: Ironically, defectors' constant search for partners to exploit leads to heterogeneous networks that improve the survivability of cooperators, compared to the traditional homogenous population assumption.When communities face the prisoner's dilemma, swift reaction to adverse ties evolves when competition is fierce between cooperators and defectors, providing an evolutionary basis for the necessity of individuals to adjust their social ties.Our results show how our innate resilience to change relates to mutual agreement between cooperators and how "loyalty" or persistent social ties bring along an evolutionary disadvantage, both from an individual and group perspective.

View Article: PubMed Central - HTML - PubMed

Affiliation: COMO, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. svsegbro@vub.ac.be

ABSTRACT

Background: In recent years it has been found that the combination of evolutionary game theory with population structures modelled in terms of dynamical graphs, in which individuals are allowed to sever unwanted social ties while keeping the good ones, provides a viable solution to the conundrum of cooperation. It is well known that in reality individuals respond differently to disadvantageous interactions. Yet, the evolutionary mechanism determining the individuals' willingness to sever unfavourable ties remains unclear.

Results: We introduce a novel way of thinking about the joint evolution of cooperation and social contacts. The struggle for survival between cooperators and defectors leads to an arms race for swiftness in adjusting social ties, based purely on a self-regarding, individual judgement. Since defectors are never able to establish social ties under mutual agreement, they break adverse ties more rapidly than cooperators, who tend to evolve stable and long-term relations. Ironically, defectors' constant search for partners to exploit leads to heterogeneous networks that improve the survivability of cooperators, compared to the traditional homogenous population assumption.

Conclusion: When communities face the prisoner's dilemma, swift reaction to adverse ties evolves when competition is fierce between cooperators and defectors, providing an evolutionary basis for the necessity of individuals to adjust their social ties. Our results show how our innate resilience to change relates to mutual agreement between cooperators and how "loyalty" or persistent social ties bring along an evolutionary disadvantage, both from an individual and group perspective.

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Role of strategy-dependent willingness on cooperation. Fraction of cooperators as a function of T for different values of ηC (the willingness to change of cooperators) and ηD (the corresponding quantity for defectors). The remaining parameters are W = 2.5, β = 0.005, N = 103 and z = 30. The situation in which ηC = ηD = 1.0 is here used as baseline. Reducing ηD makes it easier for cooperators to wipe out defectors. Reducing ηC, on the other hand, has the opposite effect.
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Figure 2: Role of strategy-dependent willingness on cooperation. Fraction of cooperators as a function of T for different values of ηC (the willingness to change of cooperators) and ηD (the corresponding quantity for defectors). The remaining parameters are W = 2.5, β = 0.005, N = 103 and z = 30. The situation in which ηC = ηD = 1.0 is here used as baseline. Reducing ηD makes it easier for cooperators to wipe out defectors. Reducing ηC, on the other hand, has the opposite effect.

Mentions: As a first step to investigate the effect of differences in eagerness to change on the evolution of cooperation (see Methods), we assume that either cooperators or defectors have a fixed and pre-defined η (see Fig. 2). The chances of cooperators are measured by calculating the fraction of runs in which the population ends in full cooperation. Note that the adopted strategy update rule ensures that full cooperation and full defection are the only two absorbing states of the strategy evolutionary dynamics (see Methods). Fig. 2 shows that when defectors are less eager to change partners (ηD = 0.5 and ηD = 0) relative to cooperators (ηC = 1.0), cooperators ensure the stability of favourable interactions while avoiding adverse ones more swiftly; hence, assortment of cooperators becomes more effective, enhancing the feasibility of cooperation [44]. When cooperators' willingness to change is low (ηC = 0.5) or absent (ηC = 0.0) compared to defectors (ηD = 1.0), the level of cooperation decreases with respect to the situation where cooperators and defectors react equally swift to adverse ties (ηC = ηD = 1.0). Decreasing the level of adaptability of cooperators leads to their own demise. On the other hand, if we compare these results with those in which all social ties remain immutable (leading to a static network, ηC = ηD = 0, shown also in Fig. 2), the feasibility of cooperation actually increases. Why does rewiring of defector-links already improve the survival of cooperators? This latter result is a consequence of heterogeneity created by rewiring defectors. As we start from well-mixed communities of limited connectivity (see Methods), rewiring of links creates a heterogeneous environment, which always favours cooperators. Thus even when cooperators are slow adapters, they prosper at the expense of the defectors greed. Overall, our results clearly show that swift decisions concerning partner choice provide a proactive force toward the evolution of cooperation, independent of the strategy.


The evolution of prompt reaction to adverse ties.

Van Segbroeck S, Santos FC, Nowé A, Pacheco JM, Lenaerts T - BMC Evol. Biol. (2008)

Role of strategy-dependent willingness on cooperation. Fraction of cooperators as a function of T for different values of ηC (the willingness to change of cooperators) and ηD (the corresponding quantity for defectors). The remaining parameters are W = 2.5, β = 0.005, N = 103 and z = 30. The situation in which ηC = ηD = 1.0 is here used as baseline. Reducing ηD makes it easier for cooperators to wipe out defectors. Reducing ηC, on the other hand, has the opposite effect.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2576237&req=5

Figure 2: Role of strategy-dependent willingness on cooperation. Fraction of cooperators as a function of T for different values of ηC (the willingness to change of cooperators) and ηD (the corresponding quantity for defectors). The remaining parameters are W = 2.5, β = 0.005, N = 103 and z = 30. The situation in which ηC = ηD = 1.0 is here used as baseline. Reducing ηD makes it easier for cooperators to wipe out defectors. Reducing ηC, on the other hand, has the opposite effect.
Mentions: As a first step to investigate the effect of differences in eagerness to change on the evolution of cooperation (see Methods), we assume that either cooperators or defectors have a fixed and pre-defined η (see Fig. 2). The chances of cooperators are measured by calculating the fraction of runs in which the population ends in full cooperation. Note that the adopted strategy update rule ensures that full cooperation and full defection are the only two absorbing states of the strategy evolutionary dynamics (see Methods). Fig. 2 shows that when defectors are less eager to change partners (ηD = 0.5 and ηD = 0) relative to cooperators (ηC = 1.0), cooperators ensure the stability of favourable interactions while avoiding adverse ones more swiftly; hence, assortment of cooperators becomes more effective, enhancing the feasibility of cooperation [44]. When cooperators' willingness to change is low (ηC = 0.5) or absent (ηC = 0.0) compared to defectors (ηD = 1.0), the level of cooperation decreases with respect to the situation where cooperators and defectors react equally swift to adverse ties (ηC = ηD = 1.0). Decreasing the level of adaptability of cooperators leads to their own demise. On the other hand, if we compare these results with those in which all social ties remain immutable (leading to a static network, ηC = ηD = 0, shown also in Fig. 2), the feasibility of cooperation actually increases. Why does rewiring of defector-links already improve the survival of cooperators? This latter result is a consequence of heterogeneity created by rewiring defectors. As we start from well-mixed communities of limited connectivity (see Methods), rewiring of links creates a heterogeneous environment, which always favours cooperators. Thus even when cooperators are slow adapters, they prosper at the expense of the defectors greed. Overall, our results clearly show that swift decisions concerning partner choice provide a proactive force toward the evolution of cooperation, independent of the strategy.

Bottom Line: Ironically, defectors' constant search for partners to exploit leads to heterogeneous networks that improve the survivability of cooperators, compared to the traditional homogenous population assumption.When communities face the prisoner's dilemma, swift reaction to adverse ties evolves when competition is fierce between cooperators and defectors, providing an evolutionary basis for the necessity of individuals to adjust their social ties.Our results show how our innate resilience to change relates to mutual agreement between cooperators and how "loyalty" or persistent social ties bring along an evolutionary disadvantage, both from an individual and group perspective.

View Article: PubMed Central - HTML - PubMed

Affiliation: COMO, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. svsegbro@vub.ac.be

ABSTRACT

Background: In recent years it has been found that the combination of evolutionary game theory with population structures modelled in terms of dynamical graphs, in which individuals are allowed to sever unwanted social ties while keeping the good ones, provides a viable solution to the conundrum of cooperation. It is well known that in reality individuals respond differently to disadvantageous interactions. Yet, the evolutionary mechanism determining the individuals' willingness to sever unfavourable ties remains unclear.

Results: We introduce a novel way of thinking about the joint evolution of cooperation and social contacts. The struggle for survival between cooperators and defectors leads to an arms race for swiftness in adjusting social ties, based purely on a self-regarding, individual judgement. Since defectors are never able to establish social ties under mutual agreement, they break adverse ties more rapidly than cooperators, who tend to evolve stable and long-term relations. Ironically, defectors' constant search for partners to exploit leads to heterogeneous networks that improve the survivability of cooperators, compared to the traditional homogenous population assumption.

Conclusion: When communities face the prisoner's dilemma, swift reaction to adverse ties evolves when competition is fierce between cooperators and defectors, providing an evolutionary basis for the necessity of individuals to adjust their social ties. Our results show how our innate resilience to change relates to mutual agreement between cooperators and how "loyalty" or persistent social ties bring along an evolutionary disadvantage, both from an individual and group perspective.

Show MeSH
Related in: MedlinePlus