I could be wrong, but I thought survival of the fittest was concerned with competition between species, not between individual members of a species.
As for whether an act is selfish or altruistic, just about every decision a person makes has a complex motivation behind it. That's why I pointed out that it exists in animals, too. I don't think a vampire bat is capable of gaining personal satisfaction out of helping another or of reasoning, "If I help him, then someone will help me if I need it," yet one bat will share its food if another doesn't have any.