Viruses are supposed to be sleek, pared-down, dead-eyed machines. But when one microbiologist stumbled upon a GIANT virus, hundreds of times bigger than any seen before, all that went out the window.  The discovery opened the door not only to a new cast of microscopic characters with names like Mimivirus, Mamavirus, and Megavirus, but also to basic questions: How did we miss these until now? Have they been around since the beginning? What if evolution could go … backwards?