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The Evolution of Charles Darwin

In a recent issue of the London Times Literary Supplement, a reviewer of Darwin’s correspondence with Henslow marveled how the untried young man, a prospective candidate for Holy Orders, could sail away in the Beagle with nothing but courage and horse sense and without ever having had a training in natural science, and come back five years later an experienced hard-headed man of science. This brought down an indignant protest from Professor Harold Fruchtbaum who contended that, before the voyage, Darwin was one of the best trained and most experienced all-round naturalists in England; all this on the basis of his having collected pebbles and beetles, accompanied fishermen on their trawls, watched a Negro skin birds, and attended some lectures at Edinburgh and Cambridge.

The reviewer retorted that this was not the view of the man who knew him best, Henslow, who told him straight that he was not even a finished naturalist, let alone a scientist. He might have added that a few weeks before the Beagle sailed, Darwin showed by his astonishment at a remark made by Adam Sedgwick that he did not even know what science meant. Furthermore, the lectures that Darwin attended at Edinburgh disgusted him with the subjects taught to such an extent that he vowed never to touch geology again. So there was still a problem to discover what it was, in the way of observations and meditations during the voyage of the Beagle, that awakened and developed Darwin’s critical faculties to such an extent that he made such marvelous use of his unpredictable opportunities in observing and collecting just what was needed for his great contributions to science. This is where Professor Michael T. Ghiselin comes in.

In Alan Moorehead’s sumptuous book, Darwin and the Beagle, he had the opportunity to identify the stimuli to which Darwin’s senses were exposed during the voyage, but failed for two reasons. One was that Darwin’s fundamentally important contributions to geology were neglected, and, as Ghiselin shows in his splendid analysis under review here, the pattern of Darwin’s researches in geology is the key to his biological work. The other reason is that Moorehead allowed a degree of hindsight to creep into his estimates of the progress of Darwin’s thoughts, for the quotations which he gives come, not from Darwin’s diary and the letters written during the voyage itself, the only proper source of information on this question, but from books published years afterward, when Darwin had already solved the problems of evolution and natural selection. So the gap in the most important chapter in the history of ideas remained yawning open, and this Ghiselin has set out to close. This is why his book is so valuable.

Ghiselin works with bold strokes on a wide canvas, and pays particular attention to methodology, a subject sadly neglected by scientists today. He shows that “the progressive development of Darwin’s thinking—from geology to biogeography, to evolution, and to evolutionary anatomy—becomes readily intelligible when it is seen how similar were his thought processes in all these fields, and how, in several senses, one problem led to another. And his ability to transfer methodologies and theoretical points of view across disciplinary boundaries is one of the main reasons for his success.”

As for what started all this in the mind of this extraordinary and undistinguished would-be clergyman, Ghiselin is clear and convincing: it was the possession of Charles Lyell’s Principles of Geology, a work which Darwin had been specifically warned by Henslow not to believe, as well as “the active process of testing theoretical notions against concrete experience that made Darwin a scientist.” I should be inclined to add something that occurred at an even earlier stage of his life, concerning which he was later both naïve and unfair: “Nothing could have been worse for the development of my mind than Dr. Butler’s School [Shrewsbury], as it was strictly classical, nothing else being taught except a little ancient history and geography.”

At the time, 1818, few things could have been better for him, as no training in the sharp analysis of the meaning of words and the thoughts that they convey can compare with that of turning English into Latin prose. This taught him to think straight. Furthermore, nothing else was available, and Darwin should really have thanked his stars that there was no instruction in the futile backwaters of Naturphilosophie, MacLeay’s crazy Quinarian system of classification, Yarrell’s “law” that when races are crossed the characters of the “oldest” race prevail in the offspring, Cuvier’s catastrophism, or the mess that then still answered for chemistry and physics.

Even a moderate dose of Linnaeus would have done him little good, for, as Ghiselin stresses, Linnaeus was an Aristotelian, an “essentialist,” whose philosophy, like that of Plato, plays a much more important part even now in the obscurantist background of Western culture than is realized. For Aristotle, “if species change, they do not exist, for things that change cannot be defined and hence cannot exist,” Ghiselin aptly points out, adding that “the Darwinian revolution thus depended upon the collapse of the Western intellectual tradition.”

There was, however, an important lacuna in Darwin’s education for, as he sadly regretted later, he was not taught any of the principles of mathematics. Who knows whether, if he had been, he might have discovered Mendel’s law of heredity for himself: he eventually had most of the evidence in his hands from his own experiments, but he lacked the idea, which was what Mendel had in this head before he made his experiments. So perhaps, in the circumstances, Lyell’s book was the best thing for him; as Ghiselin says, “no teacher was necessary, and it was an education of the first rank.”

Darwin himself is not helpful to anyone trying to discover what his methodology was: “his reasoning tended to be obscure.” In his Autobiography, begun in 1876 when he was sixty-seven years old, he paid unnecessary lip-service to inductive methods, once supposed to be the only respectable ones, and wrote, “I worked on true Baconian principles, and without any theory collected facts on a wholesale scale.” In a letter, also of 1876, to Henry Fawcett (now untraceable: sold at Sotheby’s on June 20, 1947), he made matters even worse by saying, “I determined to work with not a single idea in my head, and no one can know the years of blind labour I had.”

What makes all this so curious is that on September 19, 1838, he had written in his Third Notebook on Transmutation of Species: “The line of argument often pursued throughout my theory is to establish a point as a probability by induction and to apply it as hypothesis to other points and see whether it will solve them.” This is an acceptable description of the hypothetico-deductive method, so clearly defined by Sir Peter Medawar in his Induction and Intuition in Scientific Thought, where he pointed out that a man of science would be regarded as long overdue for leave if he professed to establish Laws of Nature by induction.

This is borne out by another passage in the same Autobiography where Darwin said, “I have steadily endeavoured to keep my mind free, so as to give up any hypothesis, however much beloved (and I cannot resist forming one on every subject [my italics]), as soon as facts are shown to be opposed to it.” As if this were not enough to contradict what he wrote in 1876, there are two letters from Darwin that bear very closely on the question. One, to Henry Walter Bates (November 22, 1860), contains the statement: “I have an old belief that a good observer really means a good theorist.” The other, to the self-same Henry Fawcett, but fifteen years earlier than that quoted above (September 18, 1861), really dismisses “Baconian methods” (which, in any case, were not owed to Francis Bacon): “About thirty years ago there was much talk that geologists ought only to observe and not theorize; and I well remember someone saying that at this rate a man might as well go into a gravel pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service.”

What all this means is that Darwin, like most scientists, was from time to time a victim of self-deception for not thinking deeply enough about methodological policy. When off his guard he blurted out unfashionable truths about scientific method, and in his work he was guided by an uncanny dumb sagacity, a wisdom, for which Ghiselin probably awards him too much conscious power of systematization. But he allows for this in his Conclusions, where he says, “Perhaps he was gifted with enormous power of intellect, and if so, he was indeed a remarkable man. Alternatively, he somehow accomplished all his feats of reasoning in spite of his limitations; if this latter possibility be accepted, we have reason to esteem him all the more.”

The most important field in which to discover and analyze the train of Darwin’s thoughts is his elaboration of the principle of natural selection. I labored for years to decipher Darwin’s atrocious handwriting in his Notebooks on Transmutation of Species, and found a number of entries that satisfied me that, at least a year before he opened Malthus’s book, he had grasped the essential principle of natural selection in regard to the crucial importance of adequate adaptation to ecological niches and reproductive success. Many biologists agree with me, but this evidence does not satisfy Ghiselin, who, with his formidable armament of philosophy, logic, and psychology, does not hesitate to hand out the lemons: “One might think that such a picture of well-adapted species replacing the inferior ones was an adequate conception of natural selection.” Alas, he comments, biologists who think like this “are grievously in error.”

As Ghiselin defines it, “natural selection is differential reproduction with its causes, nothing more.” But what, other than differential reproduction, is the meaning of the note in telegraphic style that Darwin wrote in early summer 1837: “With respect to extinction we can easy see that variety of ostrich Petise may not be well adapted, and thus perish out, or on the other hand like Orpheus being favourable, many might be produced”? That he had, by himself, grasped the principle of natural selection follows from another remark in his letter of 1876 to Henry Fawcett: “I clearly saw that selection was man’s chief means. When I had got thus far I strongly suspected that this was the key to nature’s work.” There is also the note which on December 14, 1854, he scribbled on the front cover of his Third Notebook: “Towards close I first thought of selection owing to struggle.” This unfortunately does not pinpoint the date, which must lie between July 15 and October 2, 1838.

But Ghiselin attributes great importance to the effect produced on Darwin by reading Malthus’s Essay on the Principle of Population, partly because of the stress laid on Malthus by Darwin. Ghiselin is here referring to the famous passage in the Autobiography which runs:

I soon perceived that selection was the keystone of man’s success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me. In October [really September 28], 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under the circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species. Here, then, I had at last got a theory by which to work.

From this passage some commentators have deduced that it was from Malthus that Darwin derived his principle of natural selection. As I have said above, this is quite false: Malthus had not the slightest idea of natural selection and would have been horror-struck at the notion of evolution. What Darwin got from Malthus was something that Malthus knew nothing at all about, and about which he was not writing: how natural selection is enforced on plants and animals in nature. The historian of ideas has a pretty problem in analyzing the nature of Darwin’s debt; for Malthus’s proposition that man’s poor were doomed to misery and even famine if they did not control their rate of increase, allegedly because the rate of increase of food-stuffs for human consumption could not keep pace with it, was false.

Even today, nobody knows by how much human food supplies could be artificially increased (and what increase of food supplies is other than artificial?) if they benefited from sufficient expenditure and priority. But, by what L. Z. Freedman and Anne Row have aptly called an “analogical leap,” Darwin saw at once that plants and animals, incapable of artificially increasing their food supplies, were inevitably doomed to high mortality rates, which would affect principally the less well-adapted.

Ghiselin, however, sees something more in Darwin’s debt to Malthus: it “provided the stimulus for conceiving of species in a manner totally different from that which had traditionally prevailed. The innovation may be summed up in a single word: population.” Ernst Mayr has well shown the importance for biology of the substitution of the concept of population for typological thinking; and Ghiselin’s contention that “upon reading Malthus, his [Darwin’s] attention was drawn to the long-term effects of differences between individuals upon the population,” is deserving of the closest attention. But how can he be sure that Darwin had not already thought of it before reading Malthus?

I ask this question because I succeeded at length in finding the key pages of Darwin’s Third Notebook, which he had scribbled immediately after reaching page six of Malthus’s book, and then, as was his method, cut out for use in the large book on species that he began to write in 1856. (The excised pages are published in the same Bulletin as the other notebooks, but seven years later. It is not apparent that Ghiselin is aware of them.) The relevant passage, obviously scribbled under the stress of excitement on September 28, 1838, runs:

…take Europe on an average every species must have same number killed year with year by hawks, by cold &c—even one species of hawk decreasing in number must affect instantaneously all the rest. The final cause of all this wedging must be to sort out proper structure and adapt it to changes.

He is clearly thinking of populations here, and it is difficult to believe that he had thought all this out in the short time between reading page six of Malthus and writing his note. It is a perfect example of what Ghiselin calls the conception “of species as units of interaction composed of biological individuals.” For the rest, it is interesting to see how decidedly Darwin took steps to dissociate himself from the policies that Malthus had set out to present in his book.

On the question how natural selection can “act” on an organism, Ghiselin says, “One might think that there must be some agent or force to be identified with the name. But this would be absurd, for natural selection is not a force or a tangible object, and it does not act upon organisms like a potter’s hands molding clay.” Purity of thought may necessitate such a statement, but, if so, the first victim to fall under this ax of absurdity is Darwin himself, because in the excised page referred to above, he continued, “One may say there is a force like a hundred thousand wedges trying to force every kind of adapted structure into the gaps in the economy of nature, or rather forming gaps by thrusting out weaker ones.” This is the first description of selection pressure, and we may ask if anything can exert pressure that is not a force. Meanwhile, R. A. Fisher and J. B. S. Haldane have measured selection pressures, and their results have been of the greatest value to evolutionary studies, whether the notion that natural selection is a “force” is “absurd” or not.

One of the most valuable traits in Darwin’s mental make-up was his full agreement with the principle of Oliver Cromwell’s speech to the Scottish commissioners: “I beseech you in the bowels of Christ to consider it possible ye may be mistaken.” Darwin was always testing the links of his arguments to see if he could break them, and this acquires additional interest from Sir Karl Popper’s principle that science is an asymmetrical province of human intellectual endeavor where propositions can be disproved but never proved. I have heard Popper say that he came to this conclusion because of what Einstein had done to Newton. That may be all very well for physicists, but as a biologist I will not accept Popper’s principle for one moment. If any competent scientist investigates, say, the morphology of the reptilian jaw hinge and of the mammalian ear ossicles, he cannot fail to be satisfied with the positive proof that the latter has evolved from the former, and nothing will disprove this. Ghiselin follows Popper and says that “a theory is not scientific unless it is possible to refute it.” I can think of many propositions in Holy Writ that I can refute: does this mean that they are “scientific”? Surely, Ghiselin means that a scientific theory is susceptible of disproof; and I should add, of proof, also.

Ghiselin is nothing if not downright in his statements, and many are valuable for their vigorous striking of nails right on the head. But there are occasions when he might have added more water to his whiskey. For example, “The real reason why Haeckel has been so unjustly criticized, however, has little to do with the truth or falsehood of his biological theories. Haeckel has been persecuted because he was a popular leader in the nineteenth century struggle against Prussian despotism.” I do not think that many people have criticized Haeckel’s work adversely as much as I have; but I do not recognize myself in the condemnation just quoted. I reject Haeckel’s theory of recapitulation—“Ontogeny is a concise and compressed recapitulation of phylogeny”—because my researches satisfied me that this was not true and that ontogeny was no such thing. It is, indeed, often a repetition, not a compressed and concise recapitulation, in the embryonic development of a descendant of developmental stages in the embryonic development of the ancestor, from which it deviates later or sooner.

Darwin himself recognized in his Sketch of 1842 that during its embryonic development an animal does not climb up its phylogenetic tree: “It is not true that one [form in its development] passes through the form of a lower group, though no doubt fish more nearly related to foetal state. (They pass through the same phases, but some, generally called the higher groups, are further metamorphosed).” It was later that Darwin accepted the unfortunate views of Louis Agassiz, Fritz Müller, and Ernst Haeckel.

Repetition of ancestral developmental stages, not their abbreviated recapitulation, is the kernel of the evidence that Darwin was the first to draw from embryology, to show that embryonic similarity was a consequence of heredity in community of descent, and evidence for evolution. For all Haeckel’s thumping, what he said was not true to fact, and it cloaked the recognition of the incorrectness of his principle that the young of the descendant represented the adult of the ancestor (and that evolutionary novelties were tacked on to the terminal stages of life histories). On the contrary, evidence accumulates more and more that in the successful groups of animals it is the adult of the descendant that resembles the young of the ancestor (and that evolutionary novelties can arise at any and all stages of the life history). Adult modern man has the smooth forehead of his young australopithecine ancestor; the spiral twisting of the snail first appeared in the early larval stage of its ancestor.

Finally, Haeckel’s sibylline statement that phylogeny was “the mechanical cause of ontogeny” (Ghiselin will not disallow that some meaning of the word “cause” might here be valid), delayed the start of the study of Entwicklungsmechanik, as its virtual founder, Wilhelm His, showed. If embryos develop as they do because the adults of their ancestors evolved as they did, it would be a waste of time and an error of principle to look for the causes of embryonic development in physical, chemical, or even biological factors operating de novo on each embryo. Criticism of Haeckel is a matter of embryology, not of opposition to Prussian despotism, aristocratic privileges, or ecclesiastical tyranny.

I hope I have said enough to show how thought-provoking and therefore valuable Ghiselin’s book is: “The fact that a theory is accepted by all may only mean that everybody has made the same blunder.” One of his last pronouncements is not the least important, when he says that “The Origin of Species is less to be valued for the answers it gives than for the questions it asks.” I think that the same could be said of Ghiselin’s book.

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