Darwin Had the Enlightenment adequately prepared 19th century readers for Darwin's Origin of the Species? The Enlightenment view of the science of life was neatly summed up by Diderot in his Encyclopedia, in many ways a signature product of the Enlightenment's dedication to setting forth the foundations of human knowledge. As Diderot notes in his prefaratory comments, what we call biology falls under the heading of "Natural History":

The divisions of natural history derive from the existing diversity of the facts of nature, and the diversity of the facts of nature from the diversity of the states of nature. Either nature is uniform and follows a regular course, such as one notes generally in celestial bodies, animals, vegetables, etc.; or it seems forced and displaced from its ordinary course, as in monsters; or it is restrained and put to different uses, as in the arts. Nature does everything, either in its ordinary and regular course, or in its deviations, or in the way it is employed. (Diderot xlvii)

The divisions in knowledge observed here are not, in general, those that we in 2012 would be accustomed to employ. The category of the "monstrous" or the "prodigious" seems to have been a temporary catch-all, intended to cover those things that might not otherwise fit into scientific taxonomies -- indeed, in a time when the genetic basis of Darwin's theory of natural selection is the most closely studied aspect, the monstrous nature of genetic mutation may in some sense remain a violation of natural order, but it is a violation whose regular occurrence must be built into the process, as an accepted deviation that allows the natural process to carry on. But before Darwin, the commitment existed to state that "Nature does everything, either in its ordinary and regular course, or in its deviations." I would suggest that this was, in some sense, sufficient to have prepared a readership intellectually for The Origin of Species. In some sense, Darwin's anticipation of objection was instead due to the sense that, in laying out the theory of natural selection, he was violating a taboo.

The easiest way to understand what sort of conclusion Darwin believed the reader ought to draw from The Origin of Species is to examine Darwin's own conclusion. The final paragraph of the work takes some care to situate Darwin's hypothesis within the traditions of the Enlightenment and the Scientific Revolution:

It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved. (Darwin XV)

The rhetorical strategy of this passage is quite interesting to observe. Darwin begins by offering an ordinary natural scene, one which any reader in England (and most readers elsewhere) would find familiar enough: an ordinary riverbank, with the rather humble natural life it exhibits. This simple sketch, however, suffices to remind the reader of the complex system of interactions within so limited a system: the birds may eat the worms, the action of worms in the soil provides nutrient for the plants, and so on. The only thing missing from the scene is Charles Darwin sitting under the tree, and an apple falling onto his head, as if to say: "Compare yourself to Sir Isaac Newton!" Because this is precisely the underlying argument, made mostly by analogy and allusion, which Darwin makes in this conclusion. From a riverbank scene as humble as Newton's...

He recapitulates in brief summary form the evidence for such laws that could be glimpsed even in the riverbank scene. But the analogy between Darwin and Newton is fairly obvious to a reader well-versed in the sciences of the Enlightenment. In Newton's case, the laws of physics were offered up in such a way that permitted of seemingly self-evident proof, whether mathematical or easily observed (as with the famous apple as a symbol for gravitation). But Newton also famously made the claim for his own scientific discovery as being due largely to "standing on the shoulders of giants": Newton's laws of physics were, in most important conceptual ways, preceded by Kepler's laws of planetary motion. The earlier scientific theory provided, in some important way, a template for acceptance of the later -- thus it becomes evident in Darwin's conclusion that Newton's science is very much his model, although this is not stated outright.
It is worth recalling, however, that Newton had spent more of his career doing work in theology rather than science -- Newton wrote earlier in the scientific revolution when theology itself was still considered a valid part of the sciences. By Darwin's day, theology sits uneasily with science. If the pious reader is inclined to find Darwin's conclusions rather shocking, by presenting a humble riverbank as evidence of massive laws of natural selection and a struggle for life, at least insofar as God's grandeur is concerned, Darwin meets the objection in advance by saying that "there is a grandeur in this view of life" even if the way in which it demonstrates the grandeur of the "Creator" (referenced later in the sentence) is notably different from the way in which the Bible might view such things. But Darwin is anticipated here by a long process of the "domestication" of theological thinking toward scientific thinking. In particular, Campbell notes how Darwin's style of argument works around the existing "natural theology" school of William Paley, which posited a "watchmaker God" not inconsistent with the laws Darwin describes:

The question of how to draw proper analogies between the human and the divine intellect had been a central topic of Western theological reflection at least since the time of Aquinas. As William Placher has summarized, a decisive misunderstanding, beginning with Cajetan, of the negative theology of Aquinas's five proofs produced a tradition of commentary, both Catholic and Protestant, that drew increasingly rigorous and exact analogies between the divine and the human intellect…William Paley's watchmaker God is but a further example of the "domestication of transcendence," and the passage that immediately follows Darwin's momentary, and purely tactical, questioning of this process completes the descent of a once great tradition into banality. (Campbell 228)

The "watchmaker God" is, of course, easily supported by the earlier scientific revolutions, and scientific laws, posed by the likes of Kepler and Newton. We do Darwin a disservice by assuming that his readers were shocked outright by his thesis, simply because it contradicted the Biblical Book of Genesis. Kepler and Newton had established that there was order in planetary and physical motion: the idea of a God who had designed such things was to a certain extent reinforced by their laws, and it was not lost on earlier physicists that the Bible presents a God who creates light before creating the sun. What Darwin had to overcome was not Biblical literalism so much as the shock which took away human uniqueness in creation. To a certain degree, he maintains that sense of human uniqueness by invoking the Creator, and invoking other scientific laws, at his conclusion: after all, the birds and the worms and the plantlife on the humble riverbank are not engaged in theological anxiety. That is unique to the species that is capable of reading, or writing, a book like Darwin's.

The final sentence of Darwin's book, though, makes the analogy to Newton explicit while not invoking him by name. Instead, he evokes the picture of Earth itself "circling on according to the fixed law of gravity" (even if the imperfection of such circles, and the recognition of elliptical orbits, were the first steps taken in the scientific revolution to overturn a simplistic Biblical literalism). The grandeur of this scene evokes, of course, processes that involve such long periods of time and such large-scale phenomena that human perception itself is asked to shrink in humility.…