Darwin and Natural Selection
In his 1859 book On the Origin of the Species, Charles Darwin outlined his theory of natural selection. Darwin's natural selection has been called the cornerstone of modern evolutionary biology, a revolutionary advancement in man's understanding of the natural world. Darwin saw natural selection as akin to artificial selection, better known as selective breeding.
Darwin's theory of natural selection states that there is variation within all populations of living organisms. Some of these variations occur because of mutations, which can be then passed on to offspring, if the new variation proves to be better at allowing for the survival of the organism. For example, a small creature that is able to run fast has a better chance of surviving predators and thus a better chance of passing on that trait through reproduction.
Natural selection, according to Darwin, can act upon any phenotypic trait, such as eye color. Additionally, the environment can apply special pressure on which traits are passed on. Overall, however, most natural selection does not produce new variants, but rather seeks the maintenance of the status quo, eliminating those organisms that are genetically or adaptively inferior. Herbert Spencer coined the phrase "survival of the fittest" in order to describe the process of natural selection.