Wednesday, February 13, 2013

Voilà! Evolution by Means of Natural Selection

Exploring Darwin's Journey Towards the Theory of Evolution, 

Part 2 (View Part 1)

Today, we continue our exploration into the manuscripts that tell the story of Darwin's journey towards the theory of Evolution by means of Natural Selection. Yesterday, David Kohn, Director of the Darwin Manuscripts Project, discussed the first two of these four manuscripts: excerpts from "Ornithology Notes" and his "Transmutation Notebook D."

Today, we explore "Principles of Divergence" and Darwin's "Origin Manuscripts."

Celebrating Darwin Day. By David Kohn. Director, Darwin Manuscripts Project, Part 2

Principle of Divergence. Natural Selection Portfolios II 

(Cambridge University Library, DAR 205.5: 148 For the whole of DAR 205, Darwin’s divergence portfolio, see

Principles of Divergence Portfolio. Pg. 148. Cambridge University Library.

Darwin finished his last notebook in 1839 and waited until 1842 to write a first short essay and until 1844 to write a much longer essay. Then it isn’t until 1854 that he returned in earnest to work on what became the Origin, published in 1859. There are many reasons for all these obvious intervals and gaps. But let’s focus on one big reason, namely: as a comprehensive explication of evolution, the theory even in 1844 was incomplete. For all that Darwin had fully worked out natural selection—which explains the origin of adaption—between 1838 and 1842, yet we can see in retrospect that natural selection wasn’t sufficient to explain how new species are formed. Nor did natural selection explain the principle behind the irregularly branched tree of life that Darwin first drew back in 1837.  According to his autobiography, this big intellectual gap did not dawn on Darwin until the 1850s.

I overlooked one problem of great importance; and it is astonishing to me, except on the principle of Columbus and his egg, how I could have overlooked it and its solution. This problem is the tendency in organic beings descended from the same stock to diverge in character as they become modified. That they have diverged greatly is obvious from the manner in which species of all kinds can be classed under genera, genera under families, families under sub-orders, and so forth; and I can remember the very spot in the road, whilst in my carriage, when to my joy the solution occurred to me; and this was long after I had come to Down. The solution, as I believe, is that the modified offspring of all dominant and increasing forms tend to become adapted to many and highly diversified places in the economy of nature.  (Autobiography 120-121)  

What intrigues me about this explanation of how the principle of divergence originated is Darwin’s memory of ‘the very spot in the road, whilst in my carriage, when to my joy the solution occurred to me’.  Did this really happen? Did he have a eureka moment riding in his carriage? For good reason, historians don’t like to trust autobiographical accounts. Darwin’s memory has been proven inaccurate more than once. And yet, let me rush in where wiser scholars may fail/fear to rush. In Darwin’s Natural Selection Portfolios II, there is a series of 15 loose notes, all related to divergence, all dated October to November 1854, and all written on identical grey paper. But one of these notes is written in pencil rather than ink. Unlike any of the other notes in the 1854 series, Darwin’s hand writing here is exceedingly ‘jumpy’.  Could this be the manuscript record of the carriage ride? The text reads:

We include all in class, as «in» Crustacea, which are connected, but yet no definition will define, — a proceeding explicable on descent.—

I suggest that this passage parallels the bolded sentences above from the Autobiography.  What I’m proposing as the carriage-ride note is a succinct statement of the problem or challenge of divergence—how to make the apparent "connectedness" of "all in class" more than just "heraldic", but actually "explicable" on descent. The succeeding flood of grey-paper notes contain elements of Darwin's solution—that is, the principle of divergence, which probably began to come into focus for him after he stepped down from his carriage. I think in this scrap of paper, we’ve again caught Darwin in the act of being Darwin.

Surviving draft manuscript sheets of the Origin of Species

(American Philosophical Society Library, BD 25.57 and Cambridge University Library, DAR 185: 109a (6v). For the entire known collection of Origin sheets see

Origin Manuscript. Pg. 224. American Philosophical Society Library.
The first edition of the Origin is a book of 490 pages. So Darwin’s hand-written draft must have been a respectable pile of paper. Yet for all the voluminous size of the Darwin archive, only some 30 sheets of the Origin survive. Happily, my favorite passage in the book is one of the five sheets owned by the American Philosophical Society Library in Philadelphia. Here is the passage:

Natural selection tends only to make each organism as perfect «as», or slightly more perfect than, the other inhabitants of the same country, with which it has to struggle for existence. And we see that this is so in nature.

This comes from Chapter VI, entitled ‘Difficulties on Theory,’ which perhaps could be more aptly called ‘Difficulties Conquered.’ The difficulty Darwin sought to overcome here was the appearance of perfection in nature, a concept invoked in the natural theology that Darwin encountered as a student in the work of William Paley. I am drawn to this passage because here Darwin pursues a metaphysical implication of his theory. He argues, rather slyly, that natural selection undoes the prevailing view that adaptations are perfect. He does this by introducing a contradiction in terms. How can anything be ‘slightly more perfect’. Perfect should be perfect. But Darwin shows that the concept of natural selection makes perfection relative. To be adapted organisms need only be ‘slightly more perfect than, the other inhabitants of the same country.’ But that renders perfection in nature a baseless and useless idea.

Finally, let’s consider one of the reasons that so few Origin sheets have survived. This picture on the back of an Origin sheet in Cambridge University Library is one of several with drawings like this one showing a battle between soldiers, who we may call knights of the aubergine and the carrot. The artist was Darwin’s son Francis, who evidently was given access to pages from the manuscript version of the great book. Indeed the manuscript only survives because Francis used it for drawing paper. His father didn’t seem to care!

Aubergine and Carrot Cavalry. By Francis Darwin. Cambridge University Library.

Images in this post reproduced with the permission of the Syndics of Cambridge University Library and the American Philosophical Society Library.

We hope you've enjoyed our exploration into the insights that Darwin recorded in his manuscripts, all of which ultimately led to the publication of his theory of Evolution by means of Natural Selection. We extend a special thanks to David Kohn, Director of the Darwin Manuscripts Project, for contributing these posts, and to Cambridge University Library and the American Philosophical Society Library for the use of the manuscript images included within these posts.

Read Part 1 of this Blog Post, discussing "Ornithology Notes" and "Transmutation Notebook D."

Explore Darwin on BHL and the Darwin Manuscripts Project:

Charles Darwin's Library
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Darwin Manuscripts Project
Official Darwin Day Website

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