Fig. 2.

Depiction of the environment. The agents inhabit a 2D world. Agents earn a reward for eating berries, which regrow probabilistically after being harvested. One type of berry is poisonous, and, if collected by an agent, it diminishes the agent’s ability to gather rewards from other berries, after a delay period. If an agent eats one of the poisonous berries in the important rule condition, the agent immediately gets marked and appears in a different color to the other agents. In the silly rule condition, one additional, nonpoisonous, berry also triggers an agent’s marking. Agents are able to punish each other using a “punishing beam,” causing a loss to themselves and a larger loss to the punished agent. If a marked agent is punished, the punishing agent receives a significant reward.