title: Evil green beards: Tag recognition can also be used to withhold cooperation in structured populations.
abstract: Natural selection works against cooperation unless a specific mechanism is at work. These mechanisms are typically studied in isolation. Here we look at the interaction between two such mechanisms: tag recognition and population structure. If cooperators can recognize each other, and only cooperate among themselves, then they can invade defectors. This is known as the green beard effect. Another mechanism is assortment caused by population structure. If interactions occur predominantly between alike individuals, then indiscriminate cooperation can evolve. Here we show that these two mechanisms interact in a non-trivial way. When assortment is low, tags lead to conventional green beard cycles with periods of tag based cooperation and periods of defection. However, if assortment is high, evil green beard cycles emerge. In those cycles, tags are not used to build up cooperation with others that share the tag, but to undermine cooperation with others that do not share the tag. High levels of assortment therefore do not lead to indiscriminate cooperation if tags are available. This shows that mechanisms that are known to promote cooperation in isolation can interact in counterintuitive ways.
authors.affiliation: Research Group for Evolutionary Theory, Max-Planck-Institute for Evolutionary Biology, August-Thienemann-Straße 2, 24306 Plön, Germany; Faculty of Information Technology, Monash University, Clayton, 3121 VIC, Australia. Electronic address: julian.garcia@monash.edu.
authors.forename: Julián
authors.initials: J
authors.lastname: García
authors.affiliation: Department of Economics, Universiteit van Amsterdam, Roetersstraat 11, 1018 WB Amsterdam, The Netherlands; Program for Evolutionary Dynamics, Harvard University, 1 Brattle Square, suite 6, Cambridge, MA 02138, USA.
authors.forename: Matthijs
authors.initials: M
authors.lastname: van Veelen
authors.affiliation: Research Group for Evolutionary Theory, Max-Planck-Institute for Evolutionary Biology, August-Thienemann-Straße 2, 24306 Plön, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Traulsen
mesh_terms: D005075:Biological Evolution; D003198:Computer Simulation; D003299:Cooperative Behavior; D006801:Humans; D008954:Models, Biological; D044382:Population Groups / Q000523:psychology*; D021641:Recognition, Psychology / Q000502:physiology*; D012641:Selection, Genetic
keywords: Evolution; Evolutionary dynamics