Darwin’s Literary Models
It may not be structured like a journal paper, but On the Origin of Species was written according to classical rules of rhetoric
During his final months at Cambridge, Darwin read and was greatly impressed by John Herschel’s Preliminary Discourse on the Study of Natural Philosophy (1830). In it, Herschel lays out the approach to the exposition of scientific ideas known as vera causa, which was derived originally from Bacon and Newton. Establishing the vera causa—true cause—of a phenomenon involves three phases. The potential causal phenomenon has to be real and existing, it has to be demonstrated as capable of producing the effect under investigation, and then it has to be shown to be actually responsible. The last phase is always the hardest, and is actually impossible to realize in investigating a unique historical event that cannot be reproduced for experimental investigation. Hodge has convincingly argued that Darwin laid out the Origin along the lines of vera causa: Chapters 1 through 4 establish the existence of a cause (natural selection), chapters 5 through 13 demonstrate capability, and chapters 10 through 13 demonstrate responsibility.
But Darwin still had to argue his case for a vera causa, and here other models and approaches also may have influenced him. I will single out two. As a student at Cambridge, he had been vastly impressed with what he described as the “long line of argumentation” of William Paley’s Natural Theology (1802). This influential book, which in some ways seems more like a biology textbook than a theological work, proceeded on the synthetic mode of deductive rhetoric via a syllogism. Paley first laid down a premise that seemed irrefutable—that a complex functional device such as a watch requires an intelligent designer and creator. He then demonstrated that organisms are complex and adapted. If the existence of a watch proves the activity of a designer, then even more so does a human, or a bird. The similarity of approach to Darwin’s Origin, which also argues from a powerful analogy (artificial selection), is as striking as the dissimilarity of the two men’s conclusions.
Towards the end of his book, Paley included a section arguing against the contemporary ideas of evolution propounded by Scottish philosopher David Hume, English physician Erasmus Darwin (grandfather of Charles) and French naturalist Georges-Louis Leclerc, Comte de Buffon. One might ask why this defense was necessary, especially because it drew attention to potential weaknesses in Paley’s argument. The answer is partly that Paley was confident of his ground and partly that “refutation” was formally required. Paley’s “long argument” is an example of the neoclassical dispositio defined by Duncan and Blair, in which a jurist or preacher was instructed to set out in order: introduction, proposition (the question at hand), division (elements of the case), narration (reasoning), argument (refutation of opposing positions), pathetic part (appeal to the emotions) and conclusion. (For Cicero, the roughly corresponding parts had been the exordium, narratio, refutatio, confirmatio and peroratio.)
It is interesting, then, that in the library of the University of Cambridge there is a short note in Darwin’s hand headed “Books that I read my second year at Edinburgh” that lists, among works on medicine and travel, “Blair’s Belles Lettres.” If we look at the Origin from the point of view of rhetorical practice, we see the same convention Blair used: The Origin has its proposition (the congruence of artificial and natural selection) and its narration (chapters 3, 4 and 5). These fit Duncan’s requirement that “those propositions are always first to be demonstrated, which furnish principles of reasoning in others; it being upon the certainty of the principles made use of, that the certainty of the truths deduced from them depends.” The otherwise unusual positioning of chapters 6 through 9 is then made clear: They are Darwin’s refutation. Chapters 11, 12 and 13 are his confirmation. His final chapter even has its pathetic part in the form of the slightly flowery sentiments with which he conjures up the metaphor of the “entangled bank” and glories in the “grandeur in this view of life.”
Right from the beginning, Darwin faced a difficult problem in writing up his theory. As he noted in his Autobiography, he realized early on that it seemed “almost useless to endeavour to prove by indirect means that species have been modified.” Instead he chose (or was forced) to make a logical argument in a form of which Cicero would have been proud. Each part of his theory—variation, overproduction, the struggle for life—was true and demonstrable. The argument was irrefutable. If he had been a mathematician he would have needed only to add one final notation to page 490: Q.E.D. (quod erat demonstrandum).
All of Darwin’s books and manuscripts reveal the extraordinary breadth of his learning. But the Origin was, in every sense, both the most original and the most classical, making it an even more remarkable achievement.
- Hodge, Martin J. S. 1977. The structure and strategy of Darwin’s “Long Argument.” The British Society for the History of Science 10:237–246.
- Hodge, Martin J. S. 1992. Discussion: Darwin’s argument in the Origin. Philosophy of Science 59:461–464.
- Recker, Doren A. 1987. Causal efficiency: the structure of Darwin’s argument strategy in the Origin of Species. Philosophy of Science 54:147–175.
- Sintonen, Matti. 1990. Darwin’s long and short arguments. Philosophy of Science 57:677–689.