"And that": Halliday's logogenesis, sociogenesis, and phylogenesis in Darwin's tangled bank

The late linguist M.A.K. Halliday described the last paragraph of Darwin's Origin of Species, with its description of a tangled bank, as one of the most remarkable paragraphs in the whole of literature. Yet it appears marred by an obvious grammatical mistake. In this article, we seek to show that the apparent mistake is actually the vestige of a now extinct form of paragraph in which the structure we now reserve for a single sentence could be extended over a whole paragraph or even many paragraphs. We first zoom out to show that the final sentence makes sense in the context of the paragraph as a whole, and then zoom out again to show that the modern paragraph itself is still a work in progress. Finally, we use a comparison between English and Farsi to try to show that all such grammatical choices mediate between humans and their environment. This relationship too is a work in progress in which the grammar of a language has an important role to play.