Selfishness in certain situations gave our ancestors an evolutionary advantage. Not much beyond that though. Humanity isn't really evolving much biologically anymore, now it's our culture that is evolving. We decide what is good and bad, right and wrong, etc. Selfishness isn't really a curse since no one actually cursed us with it, our society has grown to the point that selfishness is counterproductive to the whole, which is why it is considered a bad thing.