I had this conversation with a diehard atheist a few years ago.

Would you do the noble (altruistic) thing if there was no one there to see it?

Think up some kind of scenario like this. You are on a distant planet that has space flight. You know an asteroid is going to hit and destroy the innocent population of another planet. You could ram your ship into the asteroid to deflect it, but you might die and no one would be aware of it.

Now a Christian or some other religion would believe that God is observing and will reward your sacrifice.

My diehard atheist friend said that altruism is counter evolutionary...
Of course, both the atheist and the theist could refuse to commit suicide for an unknown population. Common sense can beat altruism any time!