I saw a video about a study on Japanese villagers nearby seismic fault or volcanos. And IIRC the villagers facing the dangers directly had different tempers probably driven by the constant risks and traumas from past catastrophes, while the villagers further away and shielded by hills, were calmer.
This doesn't require genetics or epigenetics to be the cause though. For example, there's also the possibility of stressed people passing their stress onto others through their actions.
