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Open Access Research article

Cooperators Unite! Assortative linking promotes cooperation particularly for medium sized associations

Ádám Kun123*, Gergely Boza12 and István Scheuring45

Author Affiliations

1 Evolution and Ecology Program, International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg, Austria

2 Department of Plant Taxonomy and Ecology, Institute of Biology, Eötvös University, Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary

3 Parmenides Center for the Study of Thinking, Kirchplatz 1, D-82049 Munich/Pullach, Germany

4 Department of Plant Taxonomy and Ecology, Research Group of Ecology and Theoretical Biology, Eötvös University and the Hungarian Academy of Sciences, Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary

5 Konrad Lorenz Institute, Adolf Lorenz Gasse 2, A-3422 Altenberg, Austria

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BMC Evolutionary Biology 2010, 10:173  doi:10.1186/1471-2148-10-173

Published: 11 June 2010



Evolution of cooperative behaviour is widely studied in different models where interaction is heterogeneous, although static among individuals. However, in nature individuals can often recognize each other and chose, besides to cooperate or not, to preferentially associate with or to avoid certain individuals.

Here we consider a dynamical interaction graph, in contrast to a static one. We propose several rules of rejecting unwanted partners and seeking out new ones, and study the probability of emergence and maintenance of cooperation on these dynamic networks.


Our simulations reveal that cooperation can evolve and be stable in the population if we introduce preferential linking, even if defectors can perform it too. The fixation of cooperation has higher probability than that of on static graphs, and this effect is more prevalent at high benefit to cost ratios. We also find an optimal number of partners, for which the fixation probability of cooperation shows a maximum.


The ability to recognize, seek out or avoid interaction partners based on the outcome of past interactions has an important effect on the emergence of cooperation. Observations about the number of partners in natural cooperating groups are in concordance with the result of our model.