Final answer:
After a disaster, when people show increased altruism, this behavior is explained by emergent norm theory, which states that individuals react to extraordinary situations with a unique set of norms that evolve, leading to altruistic actions.
Step-by-step explanation:
The phenomenon where a sense of altruism occurs after a disaster, with neighbors helping neighbors, crime rates dropping, and increased aid is known as emergent norm theory. This theory was developed by sociologists Ralph Turner and Lewis Killian and posits that during disasters, norms within a crowd can be disparate and fluctuating, and they emphasize the importance of these norms in shaping crowd behavior. The theory indicates that people respond to the extraordinary situation with their individual set of norms, which may evolve as the situation unfolds, leading to altruistic actions and cooperation among individuals who were otherwise not connected.