I concede I was a bit carried away with the “very reason our specie has been so successful”. It is true we can’t really claim this for the reasons you pointed out. However, it doesn’t take away the fact that altruism can arise on its own in nature, and that a belief in a God is not necessary.
Well, I don’t have a particular example in mind. And I think it wouldn’t be easy to find. Why ? Not because atheism cause people to be selfish, but because most atheists don’t define themselves throught that. If an atheist sacrifice himself to save someone else, you won’t find other atheists to celebrate his sacrifice as coming from his absence of belief in god. The person and his or her bravery will be celebrated, but it’s unlikely someone emphasizes the atheism of the person because it is unimportant. You never heard of any “atheist hero” because it is the same than “left-handed hero”. What am I supposed to search for when I want to find an example ? “Atheist hero” ? “Atheist sacrifice” ? I don’t think that would return anything. I would have to go through several personal stories, looking for someone mentioning for some reason that the hero was an atheist. Sweden, Canada, France, a lot of people who don’t believe in God, there ARE a lot of non-believers who sacrificed themselves. You just can’t deny that, and you actually are insulting the memory of all these people.
A potential example who comes to my mind is Louis Slotin, a canadian nuclear physicist who saved his colleagues by holding in his hand a very radioactive source and preventing it from falling apart, then died of radiation poisoning. Was he an atheist ? A christian ? I don’t know and couldn’t find the information. My guess is atheist, coming from canada and being a scientist, but it’s really just a guess since this information wasn’t mentionned anywhere. You really have to understand that in some countries, religion is not a major issue.