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A solution to the collective action problem in between-group conflict with within-group inequality.

Gavrilets S, Fortunato L - Nat Commun (2014)

Bottom Line: We focus on the effects of the differences between individuals on the evolutionary dynamics.Similar behaviour is expected for individuals with higher motivation, higher strengths or lower costs, or for individuals in a leadership position.Our theory also provides an evolutionary foundation for classical equity theory, and it has implications for the origin of coercive leadership and for reproductive skew theory.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Department of Mathematics, National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, Tennessee 37996, USA.

ABSTRACT
Conflict with conspecifics from neighbouring groups over territory, mating opportunities and other resources is observed in many social organisms, including humans. Here we investigate the evolutionary origins of social instincts, as shaped by selection resulting from between-group conflict in the presence of a collective action problem. We focus on the effects of the differences between individuals on the evolutionary dynamics. Our theoretical models predict that high-rank individuals, who are able to usurp a disproportional share of resources in within-group interactions, will act seemingly altruistically in between-group conflict, expending more effort and often having lower reproductive success than their low-rank group-mates. Similar behaviour is expected for individuals with higher motivation, higher strengths or lower costs, or for individuals in a leadership position. Our theory also provides an evolutionary foundation for classical equity theory, and it has implications for the origin of coercive leadership and for reproductive skew theory.

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Collective action in the modified model with individual costs ci increasing linearly with rank i.Group size n=8 and egalitarian division of spoils (that is, the individual shares of the reward are vi=1/n for all i). (a,b) Summary results of the last 20,000 generations for a particular set of five runs with within-group inequality d=0.2, as a function of individual cost ci. For each run, the values are averages over individuals of rank i in all groups in the population. Values for individual runs are given by circles, the average over the five runs is given by a solid line. (a) Individual efforts xi for rank i. (b) Relative fertilities  for individuals of rank i. (c,d) Summary results over all runs for one set of parameters. For each set of runs, the values are averages over individuals of rank i in all groups in the population. Colours show the relevant amounts for individuals of different ranks, from the rank-1 individual at the bottom (red) to the rank-8 individual at the top (dark green). Each set of bars corresponds to a specific value of benefit b. Each bar within a set corresponds to a specific value of parameter d controlling differences in costs, from the smallest on the left (d=0.05; small difference in costs) to the largest on the right (d=0.8; high difference in costs). We used n equally spaced values of individual costs ci from c × (1−d)/2 to c × (1+d)/2. (c) Individual efforts xi for rank i; the height of the bar is the total group effort X*. (d) Share of reproduction for individuals of rank i.
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f6: Collective action in the modified model with individual costs ci increasing linearly with rank i.Group size n=8 and egalitarian division of spoils (that is, the individual shares of the reward are vi=1/n for all i). (a,b) Summary results of the last 20,000 generations for a particular set of five runs with within-group inequality d=0.2, as a function of individual cost ci. For each run, the values are averages over individuals of rank i in all groups in the population. Values for individual runs are given by circles, the average over the five runs is given by a solid line. (a) Individual efforts xi for rank i. (b) Relative fertilities for individuals of rank i. (c,d) Summary results over all runs for one set of parameters. For each set of runs, the values are averages over individuals of rank i in all groups in the population. Colours show the relevant amounts for individuals of different ranks, from the rank-1 individual at the bottom (red) to the rank-8 individual at the top (dark green). Each set of bars corresponds to a specific value of benefit b. Each bar within a set corresponds to a specific value of parameter d controlling differences in costs, from the smallest on the left (d=0.05; small difference in costs) to the largest on the right (d=0.8; high difference in costs). We used n equally spaced values of individual costs ci from c × (1−d)/2 to c × (1+d)/2. (c) Individual efforts xi for rank i; the height of the bar is the total group effort X*. (d) Share of reproduction for individuals of rank i.

Mentions: In another modification, we assumed that group-mates share the reward equally (vi=1/n) but differ with respect to the cost coefficient ci. This may be the case if some individuals are stronger than others, so that the same amount of effort can be less costly for them in fitness terms. In our simulations, we used costs ci that increased linearly with rank i. Specifically, we used n equally spaced values of ci from (1−d)/2 to (1+d)/2 with five different values of d: 0.05 (small differences in costs), 0.1, 0.2, 0.4, 0.8 (large differences in costs). Our major conclusions remain qualitatively valid, with low-cost individuals playing the role of high-valuation group members in the basic model (Fig. 6). Note that the model with differences in costs is mathematically equivalent to a model with a constant cost c but with differences in fighting abilities si and the total group effort defined as


A solution to the collective action problem in between-group conflict with within-group inequality.

Gavrilets S, Fortunato L - Nat Commun (2014)

Collective action in the modified model with individual costs ci increasing linearly with rank i.Group size n=8 and egalitarian division of spoils (that is, the individual shares of the reward are vi=1/n for all i). (a,b) Summary results of the last 20,000 generations for a particular set of five runs with within-group inequality d=0.2, as a function of individual cost ci. For each run, the values are averages over individuals of rank i in all groups in the population. Values for individual runs are given by circles, the average over the five runs is given by a solid line. (a) Individual efforts xi for rank i. (b) Relative fertilities  for individuals of rank i. (c,d) Summary results over all runs for one set of parameters. For each set of runs, the values are averages over individuals of rank i in all groups in the population. Colours show the relevant amounts for individuals of different ranks, from the rank-1 individual at the bottom (red) to the rank-8 individual at the top (dark green). Each set of bars corresponds to a specific value of benefit b. Each bar within a set corresponds to a specific value of parameter d controlling differences in costs, from the smallest on the left (d=0.05; small difference in costs) to the largest on the right (d=0.8; high difference in costs). We used n equally spaced values of individual costs ci from c × (1−d)/2 to c × (1+d)/2. (c) Individual efforts xi for rank i; the height of the bar is the total group effort X*. (d) Share of reproduction for individuals of rank i.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974216&req=5

f6: Collective action in the modified model with individual costs ci increasing linearly with rank i.Group size n=8 and egalitarian division of spoils (that is, the individual shares of the reward are vi=1/n for all i). (a,b) Summary results of the last 20,000 generations for a particular set of five runs with within-group inequality d=0.2, as a function of individual cost ci. For each run, the values are averages over individuals of rank i in all groups in the population. Values for individual runs are given by circles, the average over the five runs is given by a solid line. (a) Individual efforts xi for rank i. (b) Relative fertilities for individuals of rank i. (c,d) Summary results over all runs for one set of parameters. For each set of runs, the values are averages over individuals of rank i in all groups in the population. Colours show the relevant amounts for individuals of different ranks, from the rank-1 individual at the bottom (red) to the rank-8 individual at the top (dark green). Each set of bars corresponds to a specific value of benefit b. Each bar within a set corresponds to a specific value of parameter d controlling differences in costs, from the smallest on the left (d=0.05; small difference in costs) to the largest on the right (d=0.8; high difference in costs). We used n equally spaced values of individual costs ci from c × (1−d)/2 to c × (1+d)/2. (c) Individual efforts xi for rank i; the height of the bar is the total group effort X*. (d) Share of reproduction for individuals of rank i.
Mentions: In another modification, we assumed that group-mates share the reward equally (vi=1/n) but differ with respect to the cost coefficient ci. This may be the case if some individuals are stronger than others, so that the same amount of effort can be less costly for them in fitness terms. In our simulations, we used costs ci that increased linearly with rank i. Specifically, we used n equally spaced values of ci from (1−d)/2 to (1+d)/2 with five different values of d: 0.05 (small differences in costs), 0.1, 0.2, 0.4, 0.8 (large differences in costs). Our major conclusions remain qualitatively valid, with low-cost individuals playing the role of high-valuation group members in the basic model (Fig. 6). Note that the model with differences in costs is mathematically equivalent to a model with a constant cost c but with differences in fighting abilities si and the total group effort defined as

Bottom Line: We focus on the effects of the differences between individuals on the evolutionary dynamics.Similar behaviour is expected for individuals with higher motivation, higher strengths or lower costs, or for individuals in a leadership position.Our theory also provides an evolutionary foundation for classical equity theory, and it has implications for the origin of coercive leadership and for reproductive skew theory.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Department of Mathematics, National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, Tennessee 37996, USA.

ABSTRACT
Conflict with conspecifics from neighbouring groups over territory, mating opportunities and other resources is observed in many social organisms, including humans. Here we investigate the evolutionary origins of social instincts, as shaped by selection resulting from between-group conflict in the presence of a collective action problem. We focus on the effects of the differences between individuals on the evolutionary dynamics. Our theoretical models predict that high-rank individuals, who are able to usurp a disproportional share of resources in within-group interactions, will act seemingly altruistically in between-group conflict, expending more effort and often having lower reproductive success than their low-rank group-mates. Similar behaviour is expected for individuals with higher motivation, higher strengths or lower costs, or for individuals in a leadership position. Our theory also provides an evolutionary foundation for classical equity theory, and it has implications for the origin of coercive leadership and for reproductive skew theory.

Show MeSH
Related in: MedlinePlus