Darwin recapitulates his theory of natural selection and summarizes the main points of his argument and evidence. He admits that while he has presented his theory as thoroughly as possible, gaps still remain, and objections may abound. To the best of his ability, he has answered questions concerning the infertility of hybrids, the geographical distribution of species, and the imperfections in the geological record. He argues that the principles behind his theory—variation exists in nature, species engage in a struggle for existence, struggles for survival result in competition between species, natural selection preserves advantageous variations that cause the proliferation of those variations in subsequent generations, and these variations cause divergence of groups from their predecessors, forming new species resulting from descent with modification—are strong enough to override any doubts that may remain.

Darwin wonders why naturalists and geologists had rejected his theory of descent with modification thus far. He argues that the rejection was due not to the scientific validity or invalidity of the theory but to human unwillingness to believe that species descended from one another. Partly, scientists had not yet been able to fathom the length of time that it takes new species to form. They were unable to grasp how gradually these descents have occurred. Darwin also blames this rejection on sheer stubbornness. Many simply refused to believe in the descent of species without “proof” in the form of intermediate forms. Naturalists, Darwin argues, have hidden their ignorance in the rhetoric of creation and design, restating facts about species rather than providing an explanation for their creation. With his book, Darwin hoped to influence those “flexible” naturalists who may have been more willing to agree with his theory of descent. However, he knew that many naturalists would vilify him because of stubbornness and ignorance.

Despite predicting skepticism about his theory, Darwin argues that his theory will lead to a “revolution” in science. Although he isn’t sure how far the doctrine of descent with modification extends, Darwin hypothesizes that all living beings are part of a chain of descent, possibly linking back to one original form. Once scientists accept the notion of chains of descent, he argues, they will stop arguing about the difference between varieties and species, as the exact categorization will no longer be important. Scientists will stop simply categorizing species without explanation, as Darwin’s concept of affinities (or relationships) between groups will clearly trace chains of descent. Furthermore, scientists will better understand human society, as psychologists can take into account the natural selection of mental capacities and instinct, and the descent of man can gradually be uncovered. Darwin also notes that a creator may have “breathed life” into one or more of the original species that began these chains of descent. Overall, scientists will have a greater understanding of the natural world, as they continually discover more about descent with modification and the evolution of species.


In Chapter 14, Darwin explains the larger implications of his theory, pointing out its potentially revolutionary nature. He claims that acceptance of his theory of descent with modification will shed light on the meaning of classification, the history of the natural world, and the emergence of today’s natural society. Though the Darwinian Revolution did eventually occur, it happened after Darwin’s time. Once Mendelian genetics and mutation theory were discovered, it was understood how the mechanisms of genetic variation allowed natural selection to occur.

Although Darwin is highly critical of natural theologians’ theories about the origin of species, he still implies that a creator breathed life into the first species. This may seem odd to some readers, considering that Darwin devotes much of his manuscript to refuting natural theologians’ claims that species were independently created. However, even if all of the existing and extinct species descended from one original species, Darwin’s theory does not explain the origin of that very first species. Perhaps to appease his opponents, Darwin allows for the possibility that a higher power was responsible for the origin of species. Darwin capitalizes the word “Creator,” which implies the existence of a religious God in charge of the initial origin of species. Although his mention of a creator probably had more to do with quelling opposition to his theory than expressing his own personal beliefs, Darwin leaves room for religious doctrine and evolution to coexist.

Darwin’s implicit inclusion of human beings in the scheme of evolution opened the door to controversy. He argues that all living organic beings are potentially included in this scheme and questions whether there is any limit to the theory of descent with modification. He also hypothesizes that all beings descended from one original species. Although he does not specify how humans might have evolved, Darwin clearly implies that humans are involved in his evolutionary scheme. This implication raises questions. Did humans descend from some other animal species? Are they the relatives of existing animal species? If so, how did humans develop such advanced capacities for thought and innovation (as compared to their ancestors)? Or are humans not nearly as advanced as we think we are? These questions have plagued scientists, religious leaders, teachers, and others who have considered Darwin’s evolutionary theory up to present day.

Only in the final word of On the Origin of Species, “evolved,” does Darwin make reference to evolution. In previous chapters, he uses the terms “divergence” and “descent with modification” to explain his theory of natural selection. Perhaps Darwin avoids using the word evolution in presenting his theory because of the resistance to and controversy surrounding previously proposed theories of evolution, such as those of Jean-Baptiste Lamarck and Robert Chambers. In the final sentence, however, Darwin drives home the idea that species “have been, and are being, evolved,” characterizing his own theory as one of evolution.