Or at the very least would behave exactly like I would if it came right down to it in a severe eg survival situation.
Yeah, we would - most of us anyway. The difference is that it takes the massive cortisol surge of a survival emergency to break through our social and emotional inhibitions. We are all in constant communication with our amygdala (primal 'lizard' brain) but, in everyday life, that communication goes through loads of overlying processes acquired through experience as we grow up.
Nobody knows why this differs for people with strongly variant behaviour patterns, despite having grown up in broadly similar environments. It seems clear, though, that having a reduced emotional range results in less interference between the amygdala and the pre-frontal cortex.
(I've oversimplified a lot, but it'll do. This is all going to be so interesting as scientific observation of the brain's electrical pathways improves.)
I suspect that, if you and I were in identical emergencies, your response would be marginally faster and more decisive than mine.
If somebody was standing between me and survival, I'd be more likely to try and push him out of the way while you'd just kill him! See, I'd still be weighing up whether he and I could both survive and, if not, the least harm I could do while still getting rid of him. You'd go straight to the most efficient action.