Punishers Benefit From Third-Party Punishment in Fish

In cases where uninvolved bystanders pay to punish defectors, this behavior has typically been interpreted in terms of group-level rather than individual-level benefits. Male cleaner fish, <i>Labroides dimidiatus</i>, punish their female partner if she cheats while inspecting model clients. Punishment promotes female cooperation and thereby yields direct foraging benefits to the male. Thus, third-party punishment can evolve via self-serving tendencies in a nonhuman species, and this finding may shed light on the evolutionary dynamics of more complex behavior in other animal species, including humans.