A couple of weeks ago, a friend asked whether there was a group in place to read Darwin's Origin of Species this year, on the 150th anniversary of its initial publication. I replied that I was not aware of any such group, and somehow wound up helping to found one. I had read the sixth and final edition before, and have decided to read the first edition for this group. (All editions are available for free online at Darwin Online.) We are having our initial meeting tomorrow, but I have had enough thoughts about the work that I felt it appropriate to record them here, before being shaped too much by others' interpretations.
The Introduction begins abruptly, so much so that I almost wondered whether there was a page missing in the submitted manuscript. It is written in a comparatively casual tone, almost as a letter to the reader, and nothing like one would expect of one of the most significant works of science ever published. It starts with a summary of the genesis of the work, in what would be a brief account in modern terms, and nothing short of astonishingly so in Darwin's Victorian terms. I should mention that, though I am tempted to cover this history here, it is not my point to summarise the book, so much as to critique it, from both a modern and (so far as I can succeed in placing myself into it) a contemporary context. My prior experience with it was positive enough that I would encourage others to read it for themselves; I flatter myself to think that this account might help in understanding Darwin's work, but I have no intention of replacing it. At the same time, Darwin regarded this 450-page book as an abstract, which only a Victorian could do. He apologises for not citing the work of others (although he does refer to such work frequently, and attributes it accordingly, he does not indicate where one might find it published), appealing to a lack of space -- again, a charmingly (some might say irritatingly) Victorian conceit in so large a work. I think it more reasonable to consider that Darwin was under considerable pressure to get his work published, since he had almost been scooped by Wallace. He gives an acknowledgement to his peers and mentors that (again) would be concise in modern terms, mentioning nobody by name aside from Hooker.
Then the Introduction begins as one might expect it to, setting the stage for the work to follow. Darwin first addresses the complexity not only of living things in and of themselves but as well that of their interactions with their environment and with other living things, which he supposes makes the proposition all the more marvellous that they arrived at their present state exclusively through natural processes. All this, he says, will be explained; and he feels it best to start with a discussion of a process analogous to his favoured mechanism, and so begins an outline of the book itself. The first part of the book (comprising five chapters) takes off from this point to discuss artificial selection, and moves on from there to cover variation in nature; the overproduction and differential survival of members of each successive variation; and the central principle of natural selection. He rounds this part of the book off with a discussion of the laws of variation and of correlation (of which I have more to say shortly). The second part of the book (the next four chapters) discusses possible objections to his theory: the complexity of any living thing and its constituent parts; the matter of instinct and other behavioural traits; the erection of biologically relevant boundaries between species; and the paucity of data from the fossil record. The third part of the book (another four chapters) picks up on this last theme, but move from addressing possible flaws in the theory to demonstrating its strengths: the continuity of living things from one form to another through time; two chapters on biogeography; and finally one on classification and comparative biology. Finally, he summarises the whole work in the last chapter.
Darwin finishes his Introduction with more uncharacteristic brevity, remarking with model honesty that the theory is far from finished, and while it is capable of explaining much, it does not cover everything. His last sentence is worthy of repetition: "Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification." This is remarkable especially in that Darwin is often assumed to have been a strict adaptationist -- to have held that everything in life can be explained solely through natural selection acting on existing variation. This misconception has gone to the point of modern scientists claiming exactly that being called "Darwinians". Darwin was ahead of his time in many ways, and one of them was this very conviction.
Chapter One of the book (as mentioned) covers artificial selection. I have comparatively less to say on this; it is at this point that the Victorian locks are opened and the flood of words rushes through. Stylistic considerations aside, the fact that the meat of the book begins here means that the pace must necessarily slow somewhat. My earlier impression is not contradicted, though: Darwin remains quite readable, for all his verbosity.
The first chapter is divided into several sections in the table of contents, but these are lumped together by headings in the text itself, and by the running titles at the top of the page. The first such section deals with what Darwin knew of genetics, which is almost embarrassingly incorrect. It is truly impressive how much he got wrong -- not just wrong, but at times fantastically so -- and yet he managed to draw the right conclusions from such faulty premises. Much has been said of the irony of Darwin and Mendel being contemporaries unaware of one another's work, and of how the combination of their work led to a paradigm shift in biology almost as significant as that generated by each body of work taken by itself. Darwin assumed that inheritance was an analogue matter, that traits from each parent blended together rather than existed as isolatable units, and had no explanation for such phenomena as recessive traits or chromosomal linkage. At the same time, he was quite aware that some traits did seem to be connected, and suggests something suspiciously close to pleiotropy, in which a single gene affects multiple traits -- a situation which can explain the evolution of many seemingly neutral or even deleterious traits, assuming them to be so linked to beneficial traits. Darwin is similarly aware of reversions as significant, but has no appreciation for any mechanisms behind such phenomena. Then again, he is not concerned with the mechanisms of genetics, which is perhaps why is able to be so right in his conclusions while being so wrong in his premises. Another angle that Darwin plays a fair bit on is the origin of domestic animals and plants, on which he speculates somewhat unrestrainedly, but rarely far from what has become accepted today.
The second section of this chapter deals with one particular example of domestication. Having spent five years at sea, Darwin proceeded to invest himself in studies of individual groups of living things -- beetles, barnacles, earthworms, and pigeons. The latter provide the subject of this section. Here he is on much firmer footing. Darwin impresses, perhaps ostentatiously so, with his encyclopaedic knowledge of breeds and characteristics of pigeons, and gives examples of how some of the more extravagant breeds could have come about. This blends into the third section, which expands the discussion to cover other species, and from there to the fourth, which covers the mechanisms of selection -- but from an ecological rather than a genetic point of view. The fifth and sixth sections take this further, positing that much artificial selection is unconscious. There are thus two types of artificial selection at work, one planned and rapid, the other a slow and organic extension of the collective preference of those charged with keeping living things. Throughout these sections, this is where Darwin truly shines (I have read -- though I forget where -- of Darwin being regarded as a pioneer in ecology as well as evolution); he looks best at the big picture, even while supplying a torrent of fine details. At the same time, his arguments here are obvious, which is perhaps why his work made such an impression at the time. It is impossible not to agree with him.
A seventh section concerns the "circumstances of man's selection", in which Darwin refutes the notion that many domesticated varieties arose recently because their variability manifested itself only recently. Not so, claims Darwin: rather, it is only recently that human meticulousness and record-keeping rose to the level of being able to pick out such subtle differences as were always present but insufficiently selected before. At the same time, he falters a little here, in his assessment of the degrees of variability amongst different domesticated plants and animals. It is true that (as he suggests) individual species' behavioural attributes contribute (and this is an important factor which I am not sure others had noted beforehand), but there are many more dimensions to consider. Among other things, some species simply do have a greater tendency toward morphological variation than others. Time is a factor as well: something that has been bred for thousands of years will have had the chance to diverge much further from its original form than something that has only been bred for hundreds of years. Dogs and cats illustrate both of these points: dogs are not merely more tractable animals than cats -- they are in fact more plastic as a species, and they have been domesticated for far longer than cats (or, for that matter, anything else), giving far more time in which to exaggerate that plasticity.
Finally, Darwin gives us a single-page summary of the chapter, and a pithy ending: "Over all these causes of Change I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant Power." Thus begins the book that changed biology.