I didn't mean it in the literal sense, i.e. there is actually a gene. It's a throw back in our psyche from the beginning of time.
Chimpanzee's create family groups who will regularly go on a raiding party against other Chimpanzee groups. This behaviour is also observed in other species.
It's simply the arrogance of man that believes now we claim to be civilised we have transcended such behaviour. I think it might be the case that we've simply suppressed it.
or maybe you've explained part of the reason there aren't 7 billion + Chimpanzee?