Well, actually some humans do try to save animals. Let's consider vegetarianism/veganism, by those who choose not to eat meat for the "love" of animals. Is veganism a survival mechanism for the human species?
Perhaps I'm naive, but I like to think that we humans have are not bound to our primitave urges for survival, and instead take actions such as not eating meat and sacrificing our own life to save the life of others, not out of "survival" but out of something greater.
I was talking about evolutionary psychology there, not taking into consideration behaviours motivated by higher intelligence. Perhaps different behaviours can be placed in a hierarchy, with more complex behaviours in higher levels and primary instincts at the bottom.
Sexual urges, for example, would be pretty low on the chart. We're not completely immune to those.
And in the soldier example, why would he exterminate his own chance of reproduction just to let other humans reproduce in his absence? Are you implying that this "survival mechanism for the rest of his species" somehow developed via evolution?
It was one of the things I encountered in a book I read about evolution. It said that this is probably how more "altruistic" and less selfish behaviours developed -- a desire to help the species as a whole rather than just the individual self.