Scientists have long seen a huge gulf dividing viruses from “true” living things—bacteria, protozoans, plants, animals, and fungi. Many pointed to the tiny number of genes in viruses, arguing that there was no way for them to gain more because of their peculiar way of reproducing. Because viruses hijack cells to make new viruses, they are sloppy about copying their genes. They don’t carry their own repair enzymes that can fix errors, for example. As a result, they are much more vulnerable to lethal mutations. If a virus accumulated thousands of genes, its high mutation rate would wipe it out.
