Bacteria. this word has been in the news and textbooks a lot lately. we know that some species of bacteria have evolved a resistance to antibiotics and are difficult if not impossible to kill. instead they are responsible for some potentially deadly illnesses and infections. we also know that recent biochemical discoveries have lead scientists down a path to completely change how life on earth is classified, starting with the bacteria. we have moved from a 5-kingdom system to a 3-domain, 6-kingdom system of classification. all bacteria are still known to be prokaryotes, but we know now that they differ biochemically. this phylogenic tree shows the changes in bacterial species from the ancestral species to the most current split in the modern classification system. this tree supports the theory that a) speciation results in biodiversity. b) natural selection favors the fittest. c) within a population, variation exists. d) extinction is the fate of the species that cannot adapt.