I mean, doing soemthing like that goes against the basic functioning of a "survival instinct".
It's one thing to save a member of a family or tribe but a compelte stranger perhpas even of a competing tribe?
I'll put it this way. If you were walking through a park and saw a 12 year old being raped by a man brandishing a knife. No one else is around, you don't have your mobile phone on you. For a brief moment, you see this child crying, calling for help, you know that child is scared and in great pain, what do you think you would do. The situation is dangerous as the man has knife, you could very well be killed, but you also know that when the man is finished he could very well kill this child.
What would you do?
If you had a deep sense of empathy for this child, no amount of danger would stop you from doing what was in your power to help this child. If you didn't help this child and people found out about it, you would most likely be lynched as that kind of behaviour is unacceptable in a civilised society where we are suppose to try and look out for eachother, especially children who are younger and weaker. You still have surival instinct as you personally do not want to die, but your empathy for this child would recognised that this childs survival is in your hands.
Empathy plays a great part in our moral development. Without empathy we could live without moral restraint as we wouldn't care what effect our actions have on others. These kinds of people are usually referred to psychopaths or antisocial personality disorder.