This section is from the book "Principles Of Sociology With Educational Applications", by Frederick R. Clow. Also available from Amazon: Principles of sociology with educational applications.
Natural selection is a biological term, the application of which has extended to all branches of knowledge. It is essentially very simple. It means merely that nature herself does the selecting. The constitution of the world determines what variations shall be preserved and what eliminated. In practical affairs the principle has long been followed, as is shown by such phrases as these: "cut and try," "trial and error," "let us see how it works," "let the results tell," "nothing succeeds like success." In business and the science of economics it is known as competition.
Natural selection as a definitely formulated principle began with Charles Darwin. He worked on it for twenty years in trying to explain the origin of species. At last a young naturalist, named Wallace, hit upon the same idea and wrote it out while confined to his room by illness. He had heard of Darwin's interest in species and so sent his paper to Darwin for criticism. Darwin behaved magnanimously toward his young rival. He put together some of his own statements which were already in writing so as to make a paper about equal in length to that of Wallace, and then had the two papers read at a meeting of a scientific society. That was in 1858. The next year Darwin published the Origin of Species, and the new theory was given to the world.
Natural selection, taken in connection with variation, constitutes what is usually known as evolution. Its discovery has amounted to a revolution - a mutation in human thought. Let us first see the meaning of the term as illustrated in biology. There are three necessary parts to the principle. First, there must be excessive multiplication so that the number of organisms in existence is greater than can find means of subsistence. With animals and plants this of course results from the high rates at which they are able to multiply. Then follows a struggle between these individuals for the means by which they can exist. Finally, those which are least capable perish, and the most capable survive to reproduce their kind and fill the available space.