This chapter comprises two very distinct sections. It is titled appropriately ("Recapitulation and Conclusion") although we might expect there to be less of a distinction between the two than Darwin gives us. Even then, the first part is not a proper recounting of the entire book, but a somewhat ricocheting run through most of its major concepts. Here more than before he emphasises the distinctions between common descent and special creation, finding for all cases the former to fit far better than the latter. He rightly identifies that the introduction of the supernatural into science has a tendency only to perpetuate ignorance: "But it deserves especial notice that the more important objections relate to questions on which we are confessedly ignorant; nor do we know how ignorant we are." Of the latter, he points out the identification of species as an example made far more contentious because of an assumption of independent creation. The Victorian view of diversity was that each species was separately created, while varieties (including subspecies) had arisen afterward, "by secondary causes", meaning by natural ones. Such arguments are meaningless if, as Darwin says, "species are only well-marked varieties"; indeed all controversies (and Darwin suggests that there were several) over the boundaries of extant species are meaningless.
Darwin spends most of his time here on his strengths, and especially on biogeography, but does not ignore his other evidence. The origin of modern diversity through adaptation of existing structures is evident throughout: "We can plainly see why nature is prodigal in variety, though niggard in innovation." His pioneering of ecology gets a brief mention, amounding to emphasis on the primary importance of the biotic environment to the success or failure of any species. He brings up again the "Red-Queen" nature of invasiveness: "As natural selection acts by competition, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates; so that we need feel no surprise at the inhabitants of any one country, although on the ordinary view supposed to have been specially created and adapted for that country, being beaten and supplanted by the naturalised productions from another land." It is unsurprising that we should see in this concluding chapter Darwin's least ambiguous writing, but the assertions are nevertheless uncharacteristically forceful: "The real affinities of all organic beings are due to inheritance or community of descent. The natural system is a genealogical arrangement, in which we have to discover the lines of descent by the most permanent characters, however slight their vital importance may be." There is no room for doubt here.
The conclusion section is more of a meta-study of evolution, looking at the contemporary state as well as the history and probable future of biology. It starts with an assertion that Darwin and his theory will face opposition. Some few naturalists will be persuaded by his work, he speculates, and certainly, given that the idea of common descent was much discussed, many more would already have been looking for proof, and might have their minds made up. But the most important recruits to Darwin's cause, he expects, will be the next generation. Modern creationists would actually find a friend in Darwin, had they lived then, as he suggests that we should (in their words) "teach the controversy": "I look with confidence to the future, to young and rising naturalists, who will be able to view both sides of the question with impartiality." But in our modern persective, we must bear in mind that this controversy raged some 150 years ago! Science has settled on an answer, and has moved on. On the other hand, Darwin is not content to allow his opponents to continue unchallenged, and asks them to answer some of his own questions. How did the Creator go about creating? How many forms were originally created? Were they adults, or juveniles, or seeds or eggs? If they were adults, did mammals have signs of having been gestated (in other words, did they have navels)? This section is a startling contrast to Darwin's usual demeanour. He is almost mocking in his requests, but he does not ask them without full knowledge that they are, after all, questions about the natural world, which follow logically from the theory of special creation, and which are therefore not unfair.
He then moves onto questions of his own theory. How far, he asks, can common descent be taken? Owen's work on homology makes it clear to Darwin (indeed, to the modern reader as well) that all phyla (plant and animal) have had each their own common ancestor. Darwin speculates that this can be taken further, that all animals and all plants had each a single ancestor, and probably all life, although he doubts that this can go far beyond speculation in his own time. On the finer end of the scale, he comes very close to proposing his own species concept: "Hereafter we shall be compelled to acknowledge that the only distinction between species and well-marked varieties is, that the latter are known, or believed, to be connected at the present day by intermediate gradations, whereas species were formerly thus connected." This, consistent with most modern species concepts, covers many of the points of its competitors, but places each in a different light. Extant species, says Darwin, are discontinuous from other extant species, while genealogically intermingling groups are necessarily the same species. This combines aspects of the biological and phylogenetic species concepts; whatever its utility today, it must be recognised as one of the first attempts (if not the first) to define "species", and indeed an early (although implicit) assertion that such a need exists in the first place.
It is difficult to convey how exactly Darwin can retain his customary modesty while predicting that his theory will revolutionise biology, but somehow he manages it. He sees its subjects as being "ennobled" by common descent, and that in that light, "how far more interesting ... will the study of natural history become!" Geology will be influenced as well: "The noble science of Geology loses glory from the extreme imperfection of the [fossil] record. The crust of the earth with its embedded remains must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals." In other words, what biologists knew all along to be a highly imperfect understanding of the world is not dissimilar to what geologists must come to grips with. The fossil record's scantiness nevertheless does not hide an emphasis on change over time, and although he only at most implies this, living things becomeall the more precious by their transiency: "Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness to a distant futurity."
There is a great deal of eloquence in these final pages, which I will not reproduce here; it is readily enough looked up. This amplifying rhetoric almost hides the fact that Darwin recognises this work to be a turning point in the history of science, a change in its world-view, a paradigm shift. Very, very few people can do more than try to imagine what that realisation must have felt like. I have not pursued the matter far enough to read Darwin's notes on the subject, but by all accounts he knew what he was about to do when he wrote this book. He does so with admirable humility, presents his arguments as humbly as is possible, but does not back down from its implications. Not only in how the world works, but in how to present one's understanding of it, we all have a lot to learn from him.