Although not the only agent of evolutionary change, natural selection is certainly the most important mechanism of adaptive evolutionary change in populations of organisms. Through the process of natural selection, individual organisms become better adapted to their local environment and thus acquire greater fitness, defined as an increase in reproductive success. If individual organisms vary in their ability to survive and reproduce, and those variations are inherited from parent to offspring, traits that are favored in the current biological conditions will spread in the population.

Natural selection as a means for evolutionary change in living creatures was first proposed, simultaneously, by two British naturalists, Charles Robert Darwin (1809-1882) and Alfred Russel Wallace (1823-1913), in a joint paper presented to the Linnean Society in London in July 1858. It was a case of a simultaneous discovery. Since the early 1840s, Darwin had been at work compiling his book...