Imagine the police arrest you and a colleague for some crime and offer individual deals if you will betray each other. If only one of you defects, that person goes free while the other, the cooperator, receives three years in prison. Mutual defection gets both of you a two-year sentence, and mutual cooperation results in a one-year sentence. That game theory scenario is called the prisoner’s dilemma. Versions of it, often involving many players who adapt their strategies as they repeatedly play the game, have been used to study how cooperative behavior might evolve in a population of competing individuals. Now Attila Szolnoki of the Hungarian Academy of Sciences and Matjaž Perc of the University of Maribor in Slovenia and King Abdulaziz University in Saudi Arabia have introduced deception to the game. They ran Monte Carlo simulations with up to 3.6 × 107 players interacting on a square lattice. In addition to defectors, the simulations included conditional cooperators who defect if they detect a defecting opponent, and deceptive defectors who always avoid detection, though at a cost. After playing against its four neighbors, a player could switch strategies depending on how well it did in comparison to the previous player; a randomly chosen neighbor then went next. The figure below shows snapshots from one simulation after 60 (left panel) and 100 (right panel) Monte Carlo steps; the population of cooperators (blue) grew at the expense of defectors (red), but in turn lost ground to deceptive defectors (green). The researchers found that such complex dynamics led to surprising evolutionary outcomes. For example, deception sometimes became more effective when its cost increased, and upping the likelihood of detection didn’t always promote cooperation. (A. Szolnoki, M. Perc, New J. Phys. 16, 113003, 2014.)
