If you took a census of life on Earth, you’d probably find that the majority of life forms looked like this. It’s a virus known as a bacteriophage, which lives exclusively in bacteria. There are about 10 million phages in every milliliter of coastal sea water. All told, scientists put the total number of bacteriophages at a million trillion trillion (10 to the 30th power). Bacteriophages not only make up the majority of life forms, but they are believed to have existed just about since life itself began. Since then, they have been evolving along with their hosts, and even making much of their hosts’ evolution possible by shuttling genes from one host to another. Thanks in large part to