Virii tend to evolve easier then our immune systems, think about it, the organism is less then a billionth our complexity, our immune systems alone are orders of complexity above virii, but they still evolve to battle it, and make it need back up. To self-evolve the immune system would take more chance and diesoffs then it would for the virii to randomly mutate, and gain resistance, to when it just bypasses the organisms defenses at will, see how easy it has been for the flu to come back every year? it has millions of generations in people worldwide, it never stays the same, the small organism is constantly improving, who knows, maybe in 3 billion years, the flu virus will ahve evolved into a highly intelligent being, like ourselves, and have computers, maybe we can trace ourselves back to a similar begining, where we gave squids in the first seas a cold, and they were having the same discussion on thier nuearal networks "ha ha" maybe my cold will evolve intoa higly intelligent being, and here we are, the cold, having taken over the planet, (i prefer to talk in quid, cold sounds like 'snerglebin'), and the flu gets it next....