By Darwin’s own testimony, the idea of natural selection as the mechanism of evolutionary change occurred to him upon rereading in 1838 An Essay on the Principle of Population, As It Affects the Future Improvement of Society (1798) by Thomas Malthus, a clergyman and political economist. “The doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms” is how Darwin described his theory of descent through modification by natural selection. Malthus asserted that because populations grow geometrically while crops grow arithmetically, there would be a struggle among creatures for survival. The fittest would prevail.

The thesis of On the Origin of Species by Means of Natural Selection is that species are created not by special acts of a Designer but by the process of evolution through natural selection. In each generation, more organisms are produced than can live to the point of reproducing. Those organisms that possess even a slight advantage in adapting to the demands of climate, food supply, and competition over fellow organisms (and other species of organisms) will have higher reproduction rates, will survive long enough to reproduce, and thus will pass their favored structures and instincts on to their offspring. Adaptations will accumulate over generations; internal organs, external structures, and behavior will be altered. New varieties, “incipient species” as Darwin called them, will appear and, over many generations, will come to be recognized as new species. Darwin does not explain the origin of life by his theory but rather how the diversity and complexity that is life came to be.

To speak persuasively for his theory, Darwin constructed what he described as “one long argument.” The book consists of arguments and evidence. The evidence is numerous illustrations of geological and biological facts about rocks, animals,...

Natural selection is not the only cause of evolution, merely the most important. Darwin discussed several others that may lead to transmutation but may not necessarily produce changes in the organism that are adaptive. Sexual selection resulted from competition among males for mating with females. Males that failed in the competition to secure and attract female mates had no or fewer offspring. The development of fighting or defensive organs may be explained by sexual selection. In later works, Darwin added a second kind of sexual selection, female choice or preference, which he argued explained the beauty of the male peacock tail feathers or the generally more colorful male of most bird species. Other mechanisms of evolution Darwin discussed were the alteration of parts by use and disuse (the Larmarckian idea of the inheritance of acquired characteristics), spontaneous variation (later understood as genetic mutations), direct action of the environment, and correlated variation, in which a change in one part of a structure or instinct was necessarily accompanied by a change in another part.

Beginning with the first edition of On the Origin of Species by Means of Natural Selection, Darwin addressed difficulties with his theory, and in later editions he expanded his remarks to objections that had been raised to the theory by critics. Among the objections that Darwin answered were the sterility of species when first crossed compared to the fertility...

On the Origin of Species by Means of Natural Selection may be the most important scientific book of the nineteenth century. It was the critical work of Darwin’s life and of all his books the one that most directly influenced nearly every field of philosophy. Darwin demonstrated that what appeared to be an object of design could be produced without a Designer. Not only was the tradition of natural theology and its argument for God’s existence by design threatened, but also, more important, mechanism was showed to be capable of yielding creativity. Mind could be produced by mindlessness. Darwin’s views also threatened essentialism, the doctrine, prominent since Plato and Aristotle, that each member of a class or species had some shared essence that made it a member and thereby defined the class. Darwin’s theory conceived of classes or categories as populations, in which class membership did not depend on an essence of whatever form but on members who would necessarily display variability in all of their identifying features. On the Origin of Species by Means of Natural Selection produced philosophical influences that were naturalistic, emphasizing development, function, and adaptation and that held selection as a powerful principle of change.

The influence of Darwin may be seen in the nineteenth century work of Charles Peirce, William James, and other American pragmatists who held that beliefs should be judged by their consequence;...

Appleman, Philip. Darwin. New York: W. W. Norton, 1970. A useful compilation of nineteenth and twentieth century responses to On the Origin of Species and to Darwinism as a new intellectual model.

Bowler, Peter J. Charles Darwin: The Man and His Influence. Cambridge, England: Cambridge University Press, 1996. Combines biography with cultural history. Bowler shows how Charles Darwin’s contemporaries were unable to comprehend the scientific importance of Darwin’s theory in the development of modern culture. Darwin’s relationships with other prominent scientists of the period are also portrayed.

Brackman, Arnold. A Delicate Arrangement: The Strange Case of Charles Darwin and Charles Russel Wallace. New York: Times Books, 1980. Brackman argues that Darwin and his friends conspired to deny Wallace credit for having first discovered the theory of biological evolution.

Clark, Ronald W. The Survival of Charles Darwin: A Biography of a Man and an Idea. New York: Random House, 1984. A study of Darwin’s life and work, concentrating on the genesis of evolutionary theory and its development after Darwin’s death.

Colp, Ralph, Jr. To Be an Invalid: The Illness of Charles Darwin. Chicago: University of Chicago Press, 1977. A detailed study of the various theories about what caused Darwin’s chronic, debilitating illness after the voyage of HMS Beagle.

De Beer, Gavin. Charles Darwin: A Scientific Biography. New York: Doubleday, 1965. The standard authorized biography of Darwin by an English scientist who enjoyed full access to the Darwin Papers...