The BBC had an article that kinder children are more popular. Social animals have evolved more than once (insects and mammals). As it is polyphyletic there must be an advantage to the social and altruism might not just be selfishness in disguise.
Why do all the bad guys lose in all the cartoon series and all the films? There is a saying that there is no honour amongst thieves and that is the key. That is why the bad guys never win. They lose because they always see evil in others and so they are waiting for the next betrayal. This is why the Deceptercons never win and why there are only ever two Sith. It seems that we understand the dangers of selfishness (and Libertarians fall into the same trap). The winners are the social and the collaborators and it is because humans have evolved into having to be a social animal.We cannot survive alone, we need others and that is why we can afford to have such a long time of helpless development before maturity.
The advantage we get from all this is escaping our genes and our environment. We can live in more climates and we can pass on our experience to our children. We do not have to have the hard coding of the gene.