Biology Revision for "O" level examinations

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Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift ( Berkeley )  It is a  process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency , and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations . This theory was put forward by Charles Darwin, trying to explain how evolution of species occurs . Look at an example to help make the concept natural selection clearer:  Industrial melanism is a phenomenon that affected over 70 species of moths in England. It has been best studied in the peppered moth, Biston betularia . Prior to 1800, the typical moth of the species had a light pattern. Dark colored or melanic moths were rare and were therefore collectors' items. During the Industrial Revolution, soot and other industri...