Evolution cares about how many of your offspring survive. Selfishness need not be conducive to this.

Selection, acting on the individual, selects for those individuals who act in ways that cause their own offspring to survive more. That is what I mean by selfishness. Selfish genes. Selfish memes.

Once people no longer die, selection will not have so much to do with death and reproduction, but with the accumulation of resources. Think about that, and it will become more clear that that will select directly for selfishness in the conventional sense.