Microevolution
Microevolution, broadly defined, is the inevitable small-scale changes in allele frequencies in a population within the same species. Under this broad definition, this change in overall allele frequencies occurs with every birth or death of a member of the species. In other words, some generations of people might be taller than the last or shorter than the last based on the number of individuals who happen to have the "tall" gene.
Microevolution, narrowly defined, is the theory that natural selection can, over time, increase the overall reproductive fitness of a species. [1]
Microevolution in Bacteria
Microevolution is the process by which bacteria develop resistance to antibiotics. When a colony of bacteria is exposed to an antibiotic, most of the bacteria die. However, in some cases a few bacteria have randomly mutated, usually through mistakes in copying the RNA during cell division. By pure chance, some of these mutations might include a strain of RNA that makes that particular bacterium resistant to the antibiotic. This one bacterium is then able to reproduce where the others can't. The actual probablility of a random mutation creating a bacterium that is resistant to a particular antibiotic is exptremely small, but in some cases, the number of bacteria involved is sufficient to offset the odds.
Sources:
- â Evolutionists express their theory of "microevolutionary theory that natural selection should optimize the existing genetic variation in a population to maximize reproductive success." http://www.talkorigins.org/faqs/faq-intro-to-biology.html