Almost always, genes are about potentials and vulnerabilities rather than about determinism.

Essentially, we humans live well enough and long enough, and are smart enough, to generate all sorts of stressful events purely in our heads.

Until you appreciate something crucial - It is incredibly easy to manipulate us as to who counts as an Us, who as a Them.

But if you get chronically, psychosocially stressed, you're going to compromise your health. So, essentially, we've evolved to be smart enough to make ourselves sick.

Pulling a gun's trigger can be an appalling act. But if it is suicidal drawing fire to save someone, it has an utterly different meaning. Placing your hand on someone's arm can be an act of deep compassion or the first step of betrayal. The punch line? It's all about context, and the biology of context is vastly more complicated than the biology of the behavior itself.

Hormones influencing the sensitivity of the person to environmental stimuli.

...when doing science (or perhaps when doing anything at all in a society as judgmental as our own), be very careful and very certain before pronouncing something to be a norm - because at that instant, you have made it supremely difficult to ever again look objectively at an exception to that supposed norm.