
One of the mysterious themes handled brilliantly by Zimmer is summed up in a simple question: Is a virus a true living thing—like animals, plants, fungi, bacteria, etc? Normally, we would imagine that the answer is no, since the defining aspect of a virus is that it can only "be fruitful and multiply" when it has teamed up with a living host. But, insofar as a virus carries around a specific cargo of exotic genes (quite unlike those of humans), we would be narrowing down absurdly the scope of viral studies if they were to be regarded essentially as lifeless piles of chemical substances. They are better looked upon as "almost-living" entities, which often have terrifying surprises up their sleeves. Some dog-owners say, of their dear pet: "The only thing he lacks is the power of speech." In the case of viruses, the only thing that prevents them from being looked upon as "true" living creatures is their inability to reproduce themselves autonomously in an ordinary DNA style.
Incidentally, one of Zimmer's chapters has a particularly ominous title: Predicting the next plague.
VIDEO: For obvious reasons, viruses in humans have a bad reputation. But this is a narrow vision of the relationships that exist between humans and these mysterious microscopic entities, who have provided us with certain vital genes. Zimmer talks here about archaic life-sustaining viruses in humans: