This diagram shows the similarities among 16S ribosomal RNA for cellular life forms (bacteria, archaea, and eucaryotes). Each branch is labeled with the name of a representative member of that group, and the length of the branches corresponds to the degree of difference in the rRNA sequence. Note that all the organisms we can see with the unaided eye (highlighted in yellow)—animals, plants, and fungi—represent a small subset of the diversity of life. In the two branches of the tree representing the bacteria and the eucaryotes, the branches that include known pathogens are indicated in red. No diseases are currently known to be caused by archaea, though many humans and all cows carry some types of archaea in their normal intestinal flora.