Origin of Species, 6th edition

"Origins..." impresses me as the labor of a supremely gifted naturalist unaware of his deficiencies as a scientist. His strategy to validate his claims is invariably to amass illustrations. "To treat this subject properly a long list of dry facts ought to be given." "This subject... can be treated properly only by giving long catalogues of facts." The great mass of examples he provides in support of his claims can tend to disguise the thinness of his arguments but it can't by itself validate them. Darwin's reliance on examples to validate his claims prompted his mentor Sedgwick's criticism that Darwin had the process of scientific discovery upside down. Instead of deducing from everything that is known what is to be accounted for, and then coming up with a corresponding mechanism, Darwin had come up with his mechanism first and supposed he could prove it true by weight of confirming observations. Darwin continues to admit as much in the sixth edition; "For I am well aware that scarcely a single point is discussed in this volume on which facts cannot be adduced, often apparently leading to conclusions directly opposite to those at which I have arrived."

Like other naturalists Darwin probably started out distinguishing between species on the basis of a few key characteristics. Noting how those key characteristics resembled the characteristics selected for by livestock breeders and pigeon fanciers, he set himself to find in nature some process analogous to that used by the breeders. For this process he didn't have far to look. In "Zoonomia" his grandfather Erasmus Darwin had laid out his path for him "Every individual tree produces innumerable seeds, and every individual fish innumerable spawn, in such inconceivable abundance as would in a short space of time crowd the earth and ocean with inhabitants…. This arguments only shews, that the productions of nature are governed by general laws." Such a law lay ready at hand in Malthus's statistical analysis of what limits the growth of human populations, a supposed "law" that was common knowledge in Darwin's day. To come up with his mechanism Darwin had only to take Malthus' statistical relationship between a human population's boundary and its area and extend it to populations of other living creatures. He named it "natural selection." "This is the doctrine of Malthus, applied to the whole animal and vegetable Kingdoms."

From here come the terms that still shape how we comprehend nature: "a struggle for existence," "competition for scarce resources," living creatures "adapting to their environment," resulting in those creatures being selectively culled for their relative "fitness" and, by the 6th edition, "survival of the fittest." These together lead to the "preservation of favorable races" or varieties and, in time, even of species. So far, so good, and it is hard not to agree that such a process must operate, to some extent, in the survival and reproduction of living creatures, just as friction is bound to operate when physical objects rub against one another. However, just because it is bound to operate, to some extent, does not mean friction is the primary agent responsible for the movement of an automobile, or make natural selection the primary driver of evolution. How does Darwin deal with this?  He simply says: "I am convinced that natural selection has been the most important means of modification." But why? I approached "Origins…" (for the second time) searching specifically for answers to such obvious questions. I chose to read the 6th edition of "Origins..." to get Darwin's latest thoughts on the subject. He includes scattered references to "habit" and "use and disuse," terms more associated with Lamarck, but without clearly relating them to his mechanism, or comparing their relative importance as drivers of evolution. He includes an entire chapter of answers to questions posed by readers of prior editions but curiously these do not include what I thought to be the most obvious questions. Warning: the 6th edition is the end result of five substantial editings. Darwin includes complete chapters of detail to support one or another of his claims, but he doesn't tell you upfront which. You can find yourself getting bogged down in oceans of boring detail that have nothing to do with all that interests us today, natural selection. It helps to recognize quickly which of his claims he's supporting and, if it's not natural selection, moving on.

In what does Darwin's originality lie? In "Origins..." I see him making four primary claims. One had already been well established by others, that the origin of species lay not in special creation but in natural processes operating on earlier species. Another claim, also already proposed by quite a few others, was that seeing living creatures dividing naturally into species was an artifact of human perception. Instead, individual variation among living creatures graded smoothly into varieties that graded smoothly into species. Third, and this seems to me the one assertion he had the right to suppose was original with him, was that natural selection operating on natural variation could account for most of the steps in the graduation of living creatures up to the level of species, hence the original title of his book, "On the Origin of Species by Natural Selection or, the Preservation of Favored Races [Varieties] in the Struggle for Life." His fourth claim, for me the boldest and most suspect, was that, given enough time, what accounted for the evolution of varieties and species can also account for graduations of types of living creatures all the way from the level of varieties up to entire kingdoms. That is, after explaining how natural selection can account for the evolution from individual variations to varieties and species Darwin extends the reach of his own mechanism to account for the evolution of species into genera. And beyond: "I see no reason to limit the process of modification... to the formation of genera alone." Today, though we can account for species through changing dominance among alleles of existing genes, we see less reason in extending something like that to account for the emergence of new genes.

Darwin's reasoning began with artificial selection seeming similar to the process of evolution in the wild. "At the commencement of my observations it seemed probable that a careful study of domestic animals and of cultivated plants would offer the best chance of making out this obscure problem [the means of modification and coadaptation of species]." "As has always been my practice, I have always sought light on this head from our domestic productions. We shall find here something analogous." But instead it may have led him astray. By the 6th edition Darwin has become concerned about the origin of variation. He had to explain how, despite his mechanism acting to reduce variation, new variation would emerge for it to operate on. Of the workings of artificial selection he says "inferior animals with intermediate characteristics would not have been used for breeding, and will thus have tended to disappear." Note Darwin's evaluation of animals with intermediate characteristics as being "inferior." This evaluation, applied by human breeders to livestock with intermediate characteristics, Darwin goes on to attribute to the operation of natural selection. Similarly he refers to the "acknowledged principle that fanciers do not and will not admire a standard, but like extremes.” Of how livestock breeders depend on foresight to guide their selections he says (beginning with the above quote) “As the differences became greater, the inferior animals with intermediate characteristics, being neither very swift nor very strong, would not have been used for breeding, and will thus have tended to disappear. Here, then, we see in man's productions the action of what may be called the principle of divergence, causing differences at first barely appreciable, steadily to increase, and the breeds to diverge in character, both from each other and from their common parent. But how it may be asked, can an analogous principle apply in nature?" Or, how can a process operating in nature—natural selection—mirror a process employed by breeders that’s dependent on their intent and foresight, and automatic preference for variations?

Darwin’s answer, in the 6th edition, appears to be because more creatures of a species can be accommodated in any given environment if the species diverges into a number of different varieties. Implied is, species by nature “want to” diverge into different varieties so as to become more widespread: this, Darwin claims, could drive natural selection in a manner analogous to the breeders' judgment in selecting for just those instances of a particular variation, however slight, that selected over several subsequent generations will amplify that variation into the fully realized characteristic the breeder is aiming at. Darwin is attributing to individuals in wild populations an aim akin to that of a breeder--to proliferate in distant generations--and foresight that preferentially culling average individuals and favoring those with variations in each current generation has potential for achieving that aim. But variations are generally agreed to be more likely harmful than beneficial, and candidates for evolution are denied foresight. By the 6th edition Darwin seems to have become tired of coping with unfavorable implications of his mechanism. 

Here are claims Darwin employs, in his conclusion in the 6th edition, to summarize how natural selection works. I suggest reading them as if finding them unfamiliar, and assessing afresh how reasonable you find them.

There is no reason why the principles which have acted so efficiently under domestication should not have acted under nature. In the survival of favored individuals and races, during the constantly recurring Struggle for Existence, we see a powerful and ever-acting form of Selection. The struggle for existence inevitably follows from the high geometrical ratio of increase which is common to all organic beings. The high rate of increase is proved by calculation.... As each species tends by its geometrical rate of reproduction to increase inordinately in number; and as the modified descendents of each species will be enabled to increase by as much as they become more diversified in habits and structure, so as to be able to seize on many and widely different places in the economy of nature, there will be a constant tendency in natural selection to preserve the most diversified offspring of any one species. Hence during a long-continued course of modification, the slight differences characteristic of varieties of the same species, tend to be augmented into the greater differences characteristic of the species of the same genus.

Some questions will occur to us that perhaps we shouldn’t expect Darwin to anticipate, but that are bound to color our judgments of “Origins…” For example, he now agrees that disuse of any characteristic, removing it from the operation of natural selection, will tend to lead to its loss. Then it must be natural selection acting on all the other characteristics of a creature that maintains them. That is, instead of natural selection being responsible for a spotters-guide’s worth of species characteristics, maybe half a dozen per species, it is now being made responsible for the zillions of characteristics involved in the smooth running of a giraffe, say. Though I know very little about such matters, I believe this is an instance of multivariate analysis, and there are formulae you can use to judge how efficient it can be, given how many individuals passed through how many generations with so many progeny per couple, involving variations in any of, say, 3 billion code elements. Gordon Rattray Taylor reports ("The Great Evolution Mystery") that at a conference held in the 1960s at the Wistar Institute where such calculations were presented, biologists’ expectations of natural selection were shown to be wishful thinking. 

My reaction on re-reading "Origins…" is that, the more I am exposed to explanations of how natural selection works the less I understand it. And now I find that my failure to understand it is due not so much to inadequacies in subsequent attempts to elucidate it but to weaknesses in arguments in “Origins…” itself. Given that, I see little for which to celebrate Darwin as a scientist, as opposed to his genius as a naturalist and ingenuity as a experimentalist. I suggest "Origins...", along with Darwin’s proposed mechanism, be relegated, along with "Vestiges of the Natural History of Creation," to the category of dead ends in the history of science. "It is so easy to hide our ignorance under such expressions as 'the plan of creation', 'unity of design,' etc., and to think that we give an explanation when we only restate a fact." For me the same has become true of "a struggle for existence," "survival of the fittest," and "adaptation to the environment."

 

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