Evolution of altruism

I’ve written a couple times already on how atheists can be altruistic without belief in a god or anything higher.  I thought though that I’d re-iterate it with this article which touches on several of the leading evolutionary explanations as to how altruism arose in the context of evolution.  There are also the philosophical arguments for morals, my personal inclination (and I think the majority of Western thinkers) is to follow that of Kant’s Categorical Imperative.  The only issue with moral philosophy I see is that it fails to explain animal altruism, so I think my current thoughts are following the evolutionary paths as roots for altruism and morality.