  Extortion strategies can dominate any opponent in an iterated prisoner's
dilemma game. But if players are able to adopt the strategies performing
better, extortion becomes widespread and evolutionary unstable. It may
sometimes act as a catalyst for the evolution of cooperation, and it can also
emerge in interactions between two populations, yet it is not the evolutionary
stable outcome. Here we revisit these results in the realm of spatial games. We
find that pairwise imitation and birth-death dynamics return known evolutionary
outcomes. Myopic best response strategy updating, on the other hand, reveals
new counterintuitive solutions. Defectors and extortioners coarsen
spontaneously, which allows cooperators to prevail even at prohibitively high
temptations to defect. Here extortion strategies play the role of a Trojan
horse. They may emerge among defectors by chance, and once they do, cooperators
become viable as well. These results are independent of the interaction
topology, and they highlight the importance of coarsening, checkerboard
ordering, and best response updating in evolutionary games.
