Evolutionary selection pressures act on all living organisms, regardless whether they are prokaryotic or higher eukaryotes. Selection refers to an evolutionary pressure that is the result of a combination of environmental and genetic pressures that affect the ability of an organism to live and, equally importantly, to produce reproductively successful offspring (including prokaryotic strains of cells).

As implied, natural selection involves the natural (but often complex) pressures present in an organism's environment. Artificial selection is the conscious manipulation of mating, manipulation, and fusion of genetic material to produce a desired result.

Evolution requires genetic variation, and these variations or changes (mutations) are usually deleterious because environmental factors already support the extent genetic distribution within a population.

Natural selection is based upon expressed differences in the ability of organisms to thrive and produce biologically successful offspring. Importantly, selection can only act to exert influence (drive) on those differences in...