In various chapters of this book, the ties between Bacteria, Archaea, and Eukarya have been made and are clear from the trees of life determined by ribosomal RNA genes as well as other conserved genes. Even from earlier times, trees and taxonomic schemes recognized that all life on Earth was related. This means that as we move backwards on the tree of life, we nd that humans have a common ancestor with chimpanzees. If we move farther back, we share a common ancestor with dogs, and farther back, we have a common ancestor with tomatoes. Eventually, we nd that we have a common ancestor with Escherichia coli and Salmonella. And, of course, ultimately, we all have the original cell as an ancestor. It survived and produced progeny that produced all life on Earth. We also nd that Eukarya essentially are endosymbiotic-and mutualistic-cooperating consortia of Bacteria, Archaea, and sometimes other Eukarya. The combination of microscopy, sequencing, and bioinformatics has led to these conclusions. However, in the past several decades, genomic studies have moved the investigations of evolution to another level.