Hormones influencing the sensitivity of the person to environmental stimuli.

Fossey, Fossey, you cranky difficult strong-arming self-destructive misanthrope, mediocre scientist, deceiver of earnest college students, probable cause of more deaths of the gorillas than if you had never set foot in Rwanda, Fossey, you pain-in-the-ass saint, I do not believe in prayers or souls, but I will pray for your soul, I will remember you for all of my days, in gratitude for that moment by the graves when all I felt was the pure, cleansing sadness of returning home and finding nothing but ghosts.

Give lab rats oxytocin and, according to that meme, they get better at talking about their feelings and sing like Joan Baez.

Only humans invent moralizing gods who monitor our behavior.

Brains distinguish between an Us and a Them in a fraction of a second. Subliminal processing of a Them activates the amygdala and insular cortex, brain regions that are all about fear, anxiety, aggression, and disgust.

Importantly, rather than promoting aggression, testosterone promotes whatever is needed to maintain status when challenged.

What happened in the milliseconds before a behavior to cause it? That's in the neurobiological realm.