In any case, people have tried to explain away altruism in all its forms by attributing it all to one thing, like selfishness, or God. I think it helps to step back and really think about how the development of a trait is influenced by many factors, and is not easily reducible to one idea. However we have evolved, it has happened in such a way that there are a number of ways in which we might react or behave in an urgent situation, depending on the individual and numerous other factors. It is also important to realize that natural selection isn't some kind of orchestrated process sorting out the "bad" traits from the "good" ones. Evolution is pretty random sometimes, and has resulted in an amazing diversity of behaviors and traits.
Meanwhile, John Hawks notes a new study in Nature Neuroscience that "claims to have spotted a brain correlate of altruism" -- namely, the posterior superior temporal sulcus. You can find the study itself here and a simple summary of the methodologies and results here:
The results suggest altruistic behavior may originate from how people view the world rather than how they act in it...“We believe that the ability to perceive other people’s actions as meaningful is critical for altruism,” [said one researcher].
In other news: McLean Hospital in Boston is launching a Positive Psychology institute "that will aim to teach healthcare providers and patients some of the more practical tenets of positive psychology, a mix of science and self-help that has been growing explosively in academia and building buzz in the media." This might be the first effort of its kind.