Reading an interesting article in a french science magazine and with the use of the references, other articles can be found on the internet.

Where does our moral sense come from?

If you hear a cry for help and see someone drowning, you’re going to do everything possible to save him. Is that heroism? Well, I'm afraid not. It’s just our natural aversion to see anybody hurt. Psychology demonstrates this and neuroscience confirms it.
It’s got nothing to do with moral, religion and all to do with the laws of evolution.
Tests (for instance an exercize being having a boat too loaded with people and one person is in a very bad state: would you kill him and save the others or try to save everyone) show that emotions areas of the brain are affected when a choice is made between doing nothing or killing one person to save the rest of the others.
Another inherited moral behavior is aversion towards unfair choices (that demonstrates man's need to be social).
How come there's violence in spite of the inherited moral behavior? We have a natural disposition to cooperate with someone else, like exerting domination, and violence enables to punish those who refuse cooperation, those who take advantage of the sense of fairness or revulsion towards sufferance without doing the same within that group.

Moral behaviors are known to animals and to babies who can't talk yet. No need for religion.