Particularly revealing to anyone who ever edited a book is the series of letters CD sent to Jenyns, upon his return from the voyage of the Beagle, to convince him to start, then to complete the job of describing the specimens CD called my fishes. These letters are fully documented in Burkhardt etal. (1986), with additional context provided in this book.
CD even used nationalism: For the credit of English zoologists, do not despair and give up; for if you do, then will it be said that there was not a person in Great Britain with knowledge sufficient to describe any specimen which may be brought here. (Dec. 4,1837).
As well, CD pleaded with Jenyns for the incorporation, into the fishes' descriptions, of his field notes on colours and behaviour. Jenyns went along, and this made Fish (Jenyns 1840-2) rather lively, at least by the standards of the the taxonomic literature of the time. One example, from p. 87: "In Mr Darwin's notes, it is stated that [*Salarias atlanticus] bites very severely, having driven its teeth through the finger of one of the officers in the ships company. Its two very long sharp canine teeth at the back of the lower jaw are well calculated to inflict such a wound."
The point about CD, though, is not any of this, but that he discovered *natural selection. His post-Beagle *notebooks, now available in their entirety (Barrett etal. 1987), make clear that this discovery happened in the autumn of 1838,withvarious scholars even venturing specific dates.
This led to an immediate change in the way CD read: before, he absorbed ideas from a wide range of books, almost haphazardly, with what we might wish to call an 'open mind'. He describes his reading during this period thus: I worked on true Baconian principles and without any theory collected facts on a wholesale scale...
This statement has misled many - because it describes a period which ended when CD hit on natural selection. Thereafter, his readings became more targeted, with all that he read being evaluated (often through critical *marginalia pencilled right onto the offending pages) in terms of its support - or lack thereof - for the nascent theory.
The role played by fish in this phase of CD's personal evolution is hard to pin down. The distributions of fishes clearly played an important role. Notably, CD expected isolated islands to have a relatively large fraction of endemics among their coastal fishes, and one even gets the impression, with regard to the Galapagos at least, that he expected to be able to document, using fish species distributions, the peculiar role that isolated islands play in generating biodiversity, now commonly illustrated with *Darwin's Finches. This couldn't be done at the time, owing to the state of fish *taxonomy, and CD gradually abandoned this theme. However, he continued to discuss fish *distributions when contrasting freshwater with marine habitats, and insisting that the former served as refuge to ancient *ganoid fishes, which have apparently been saved from fatal competition by having inhabited a protected station. (Origin, VI, p. 105).
In *Foundations of Origin, two manuscripts CD wrote in 1842 and 1844 to ensure that his discovery would not be lost (he had his wife promise to publish them, should he die prematurely), 'fish' also served as CD's shorthand for ancestral Vertebrates, especially in terms of their anatomy, habitat, and perceived tendency toward *hermaphroditism, a feature much emphasized in subsequent writings, and fully documented in this volume.
Also of note is CD's membership of the Strickland Commission, which originated the predecessor to the International *Code of Zoological Nomenclature (Strickland et al. 1843). None of this, however, added to our knowledge of fishes perse.
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