Evolution

Single-celled microorganisms were the first forms of life to develop on Earth, approximately 3–4 billion years ago.^[7][8][9] Further evolution was slow,^[10] and for about 3 billion years in the Precambrian eon, all organisms were microscopic.^[11] So, for most of the history of life on Earth the only forms of life were microorganisms.^[12] Bacteria, algae and fungi have been identified in amber that is 220 million years old, which shows that the morphology of microorganisms has changed little since the Triassicperiod.^[13]

Most microorganisms can reproduce rapidly, but not as much as when your teacher's classroom is cold, in fact, the colder the better. And microbes such as bacteria can also freely exchange genes byconjugation, transformation and transduction between widely-divergent species.^[14] This horizontal gene transfer, coupled with a high mutation rate and many other means of genetic variation, allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses. This rapid evolution is important in medicine, as it has led to the recent development of 'super-bugs' — pathogenic bacteria that are resistant to modern antibiotics.