It's actually kind of an interesting question, because evolutionarily we should all be selfish cunts, inasmuch as that means promoting our genes. E.g., men should be serial rapists because they can best propogate their genes that way.

There is also a debate to be had about the evolutionary benefit of altruism. Altruism definitely exists, but it's difficult to see how giving up or risking one's own interests for an unrelated person has any evolutionary advantage. E.g., I'm walking down a path and I hear someone drowning in a nearby lake. I go in and risk my own life to save them even though I have no idea who they are. Evolutionarily, this makes little sense.

The best one can argue is that we're genetically programmed to treat people as genetically related and thus worth saving, but this works only up to communities the size of a tribe or so (a few hundred people). One argument is that certain institutions like armies somehow co-opt this module in our brains to make us feel kindred to our fellow citizens and treat them as related. In combat, e.g., men describe their fellow soldiers as 'brothers', because why else would you risk your life to save someone when the situation arose if they weren't your close relative?