In my recent book, Darwin’s Bluff: The Mystery of the Book Darwin Never Finished, I argued that despite creating great anticipation for his “Big Book” on species as a follow up to the Origin of Species, Darwin never completed nor published his sequel because he realized it would not adequately address the criticisms he received in response to the Origin. I based my argument on a comprehensive reading of Darwin’s correspondence up to the year 1863. Recently, I turned up some later letters showing that Darwin’s bluff extended well beyond that year. 

The Check Is (Still) in the Mail

On November 15, 1871, the Italian botanist Frederico Delpino wrote to Darwin:

I cannot hide from you my wish to have immediate news of your valued health….I hope that you are perfectly restored now, to conduct your grand work to completion, and most of all that which I am awaiting with great suspense, — i.e. the variations of animals and plants in the state of nature.

Even though Darwin had published an expanded version of the first two chapters of his “Big Book” in 1868 as Variation in Animals and Plants under Domestication and had just come out with his massive Descent of Man and Selection in Relation to Sex, Delpino was still awaiting Darwin’s promised evidence for natural selection, evidence missing from the Origin due to its being a mere abstract. Alas, Delpino would continue to wait with great suspense, for a week later Darwin wrote back to him:

My health has been very poor all this summer, & I doubt whether I shall ever have the strength to publish on Variability under a State of Nature. Next summer or autumn I hope to publish a long Essay, the result of 5 or 6 years work, on the comparative growth, vigour & fertility of crossed & self-fertilised plants during several successive generations.

Of course, if health was truly an issue, where did Darwin find the strength to publish his two volumes on variation under domestication in 1868 and over the next three years to write and publish the nearly 250,000-word Descent, let alone the long essay he mentions to Delpino? Darwin complained to Joseph Dalton Hooker that the Descent half killed him, following with “That Devilish Descent of Man was too much for me.” But this has to be an exaggeration. If the Descent had been too much for Darwin, he wouldn’t have been able to complete and publish it. 

A Lifelong Bluff

We know from Darwin’s surviving, unfinished “Big Book” manuscript (published by Cambridge University Press in 1975) that the chapter titled “On Natural Selection” (chapter 6 in the manuscript) was completed by the late 1850s. Completing the rest of the manuscript or at least publishing the natural selection chapter as a separate essay would have required much less work than everything Darwin accomplished in the decades following the Origin, and it would have at least made good on Darwin’s promise to provide the evidence for natural selection he withheld from the Origin.

But along with the many others who awaited Darwin’s “Big Book,” Delpino’s curiosity would never be satisfied. Darwin simply abandoned the “Big Book” project. That Darwin possessed a long catalogue of facts demonstrating natural selection in action would remain just a giant bluff the entirety of his life.