In a highly evolved social animal like us, altruistic behavior in an individual would be prized by others in the band, to be used to cement alliances and as a currency to barter and trade good will. The selfish SOB never has any friends when he needs them. Good neighbor Sam will always be able to rely on his tribe/clan/collective for assistance and he will also be in a better position to influence group decisions.

We are probably all programmed with different amounts of altruism, and it is probably cultivated and transmitted culturally as well as genetically, and evolves just like any characteristic to fit the social environment as required. There is probably a trade off between pure selfishness and pure selflessness and different mixes are suitable for different social circumstances and different communities.

The important thing to remember is that, alas, even "goodness" and "decency" are just evolutionary parameters that are selected for and against as we evolve in our communities and as our communities evolve through time.