Why It Feels Good To Be Altruistic

Actually, strictly speaking, I'm not sure that this article or the research it's based on answers the implied question in the title. Why It Feels Good To Be Altruistic: "a similar pattern of brain activity was seen when subjects chose either to donate or take a payoff. Both types of decisions were associated with heightened activity in parts of the midbrain, a region deep in the brain that is known to be involved in primal desires (such as food and sex) and the satisfaction of them. This result provides the first evidence that the 'joy of giving' has an anatomical basis in the brain – surprisingly, one that is shared with selfish longings and rewards."
That's more 'how' we come to feel good about it. The why is a bigger question whose answers range from 'just do' to 'because God made it that way'. We have a big issue with confusing how and why in our culture...