  From 1837, when he returned to England aboard the $\textit{HMS Beagle}$, to
1860, just after publication of $\textit{The Origin of Species}$, Charles
Darwin kept detailed notes of each book he read or wanted to read. His notes
and manuscripts provide information about decades of individual scientific
practice. Previously, we trained topic models on the full texts of each
reading, and applied information-theoretic measures to detect that changes in
his reading patterns coincided with the boundaries of his three major
intellectual projects in the period 1837-1860. In this new work we apply the
reading model to five additional documents, four of them by Darwin: the first
edition of $\textit{The Origin of Species}$, two private essays stating
intermediate forms of his theory in 1842 and 1844, a third essay of disputed
dating, and Alfred Russel Wallace's essay, which Darwin received in 1858. We
address three historical inquiries, previously treated qualitatively: 1) the
mythology of "Darwin's Delay," that despite completing an extensive draft in
1844, Darwin waited until 1859 to publish $\textit{The Origin of Species}$ due
to external pressures; 2) the relationship between Darwin and Wallace's
contemporaneous theories, especially in light of their joint presentation; and
3) dating of the "Outline and Draft" which was rediscovered in 1975 and
postulated first as an 1839 draft preceding the Sketch of 1842, then as an
interstitial draft between the 1842 and 1844 essays.
