Darwin's Ghosts

by Rebecca Stott

  I like to think that Darwin might have recognized structural patterns in this long history of evolution and that it would have given him pleasure to see that the process of discovery did not travel in a straight line, a historical progression moving inexorably toward a final truth. Instead, like the history of species as he understood it, the story of the discovery of natural selection is a story of meanderings and false starts, of outgrowths, adaptations, and atrophies, of movements backward as well as forward, of sudden jumps and accelerations and convergences. The final stages of this story can perhaps intriguingly also be understood as mirroring what biologists now call “convergent evolution,” a process by which unrelated species sometimes acquire similar body structures; just such a convergence took place in 1858 when Darwin received Wallace’s essay and realized they had discovered natural selection simultaneously. The history of evolution ultimately testifies to the fertility of nature and its production, not only of a variety of forms and species, but also of a variety of ideas that can endlessly take new twists and turns.

  “There is grandeur in this view of life,” wrote Darwin in Origin, “with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

  If Darwin and his predecessors had the power to move forward in time, to wander in the zoology departments or laboratories of Cambridge or California, to ask questions and perhaps conduct a few experiments, they would be astonished to learn of the computer simulations and data sets and powers of verifiability that have become possible. Think what they might make of genetics, the genome project, neuroscience and cloning, of the extraordinary things that we now know to be true, via the mapping of genomes, about our kinship with animals. But think, too, of how mystified they might be, given how well they understood the great strides that are often made as a result of crossing disciplinary boundaries, by the increasing narrowness of scientific specialties; and given that all of them, except Darwin and his grandfather Erasmus, Robert Chambers, and Alfred Russel Wallace, depended financially upon powerful and influential patrons who understood what they were doing and rarely interfered with their work or asked them to account for its usefulness or applicability, they might be baffled to hear about the hours modern scientists spend filling out funding application forms and negotiating complex institutional politics. They might have asked how mavericks or iconoclasts might flourish in such conditions, or whether serendipity might happen much here. And the answer might be a predictable one: Innovative thinkers do not disappear from the history of science as the conditions of scientific discovery change. They merely adapt; they mutate into new forms.

  Appendix: An Historical Sketch of the Recent Progress of Opinion on the Origin of Species

  BY CHARLES DARWIN

  From the fourth edition of On the Origin of Species by Natural Selection, 1866, xiii–xxii

  I will here give a brief, but imperfect, sketch of the progress of opinion on the Origin of Species. The great majority of naturalists believe that species are immutable productions, and have been separately created. This view has been ably maintained by many authors. Some few naturalists, on the other hand, believe that species undergo modification, and that the existing forms of life are the descendants by true generation of pre-existing forms. Passing over allusions to the subject in the classical writers,* the first author who in modern times has treated it in a scientific spirit was Buffon. But as his opinions fluctuated greatly at different periods, and as he does not enter on the causes or means of the transformation of species, I need not here enter on details.

  Lamarck was the first man whose conclusions on the subject excited much attention. This justly-celebrated naturalist first published his views in 1801; he much enlarged them in 1809 in his “Philosophie Zoologique,” and subsequently, in 1815, in the Introduction to his “Hist. Nat. des Animaux sans Vertèbres.” In these works he upholds the doctrine that all species, including man, are descended from other species. He first did the eminent service of arousing attention to the probability of all change in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition. Lamarck seems to have been chiefly led to his conclusion on the gradual change of species, by the difficulty of distinguishing species and varieties, by the almost perfect gradation of forms in certain groups, and by the analogy of domestic productions. With respect to the means of modification, he attributed something to the direct action of the physical conditions of life, something to the crossing of already existing forms, and much to use and disuse, that is, to the effects of habit. To this latter agency he seems to attribute all the beautiful adaptations in nature;—such as the long neck of the giraffe for browsing on the branches of trees. But he likewise believed in a law of progressive development; and as all the forms of life thus tend to progress, in order to account for the existence at the present day of simple productions, he maintains that such forms are now spontaneously generated.* Geoffroy Saint Hilaire, as is stated in his “Life,” written by his son, suspected, as early as 1795, that what we call species are various degenerations of the same type. It was not until 1828 that he published his conviction that the same forms have not been perpetuated since the origin of all things. Geoffroy seems to have relied chiefly on the conditions of life, or the “monde ambiant,” as the cause of change. He was cautious in drawing conclusions, and did not believe that existing species are now undergoing modification; and, as his son adds, “C’est donc un problème à réserver entièrement à l’avenir, supposé même que l’avenir doive avoir prise sur lui.”

  In 1813 Dr. W. C. Wells read before the Royal Society “An Account of a White Female, part of whose Skin resembles that of a Negro”; but his paper was not published until his famous “Two Essays upon Dew and Single Vision” appeared in 1818. In this paper he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone. After remarking that negroes and mulattoes enjoy an immunity from certain tropical diseases, he observes, firstly, that all animals tend to vary in some degree, and, secondly, that agriculturists improve their domesticated animals by selection; and then, he adds, but what is done in this latter case “by art, seems to be done with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit. Of the accidental varieties of man, which would occur among the first few and scattered inhabitants of the middle regions of Africa, some one would be better fitted than the others to bear the diseases of the country. This race would consequently multiply, while the others would decrease; not only from their inability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbours. The colour of this vigorous race I take for granted, from what has been already said, would be dark. But the same disposition to form varieties still existing, a darker and a darker race would in the course of time occur; and as the darkest would be the best fitted for the climate, this would at length become the most prevalent, if not the only race, in the particular country in which it had originated.” He then extends these same views to the white inhabitants of colder climates. I am indebted to the Rev. Mr. Brace, of the United States, for having called my attention to the above passage in Dr. Wells’ work.

  The Hon. and Rev. W. Herbert, afterwards Dean of Manchester, in the fourth volume of the “Horticultural Transactions,” 1822, and in his work on the “Amaryllidaceae” (1837, p. 19, 339), declares that “horticultural experiments have established, beyond the possibility of refutation, that botanical species are only a higher and more permanent class of varieties.” He extends the same view to animals. The Dean believes that single species of each genus were created in an originally highly plastic condition, and that these hav
e produced, chiefly by intercrossing, but likewise by variation, all our existing species.

  In 1826 Professor Grant, in the concluding paragraph in his well-known paper (“Edinburgh Philosophical Journal,” vol. xiv, p. 283) on the Spongilla, clearly declares his belief that species are descended from other species, and that they become improved in the course of modification. This same view was given in his 55th Lecture, published in the “Lancet” in 1834.

  In 1831 Mr. Patrick Matthew published his work on “Naval Timber and Arboriculture,” in which he gives precisely the same view on the origin of species as that (presently to be alluded to) propounded by Mr. Wallace and myself in the “Linnaean Journal,” and as that enlarged in the present volume. Unfortunately the view was given by Mr. Matthew very briefly in scattered passages in an Appendix to a work on a different subject, so that it remained unnoticed until Mr. Matthew himself drew attention to it in the “Gardener’s Chronicle,” on April 7th, 1860. The differences of Mr. Matthew’s view from mine are not of much importance: he seems to consider that the world was nearly depopulated at successive periods, and then re-stocked; and he gives, as an alternative, that new forms may be generated “without the presence of any mould or germ of former aggregates.” I am not sure that I understand some passages; but it seems that he attributes much influence to the direct action of the conditions of life. He clearly saw, however, the full force of the principle of natural selection.

  The celebrated geologist and naturalist, Von Buch, in his excellent “Description Physique des Iles Canaries” (1836, p. 147), clearly expresses his belief that varieties slowly become changed into permanent species, which are no longer capable of intercrossing.

  Rafinesque, in his “New Flora of North America,” published in 1836, wrote (p. 6) as follows: —“All species might have been varieties once, and many varieties are gradually becoming species by assuming constant and peculiar characters”: but farther on (p. 18) he adds, “except the original types of ancestors of the genus.”

  In 1843–44 Professor Haldeman (Boston Journal of Nat. Hist., U. States, vol. iv, p. 468) has ably given the arguments for and against the hypothesis of the development and modification of species: he seems to lean towards the side of change.

  The “Vestiges of Creation” appeared in 1844. In the tenth and much improved edition (1853) the anonymous author says (p. 155): —“The proposition determined on after much consideration is, that the several series of animated beings, from the simplest and oldest up to the highest and most recent, are, under the providence of God, the results, first, of an impulse which has been imparted to the forms of life, advancing them, in definite times, by generation, through grades of organisation terminating in the highest dicotyledons and vertebrata, these grades being few in number, and generally marked by intervals of organic character, which we find to be a practical difficulty in ascertaining affinities; second, of another impulse connected with the vital forces, tending, in the course of generations, to modify organic structures in accordance with external circumstances, as food, the nature of the habitat, and the meteoric agencies, these being the ‘adaptations’ of the natural theologian.” The author apparently believes that organisation progresses by sudden leaps, but that the effects produced by the conditions of life are gradual. He argues with much force on general grounds that species are not immutable productions. But I cannot see how the two supposed “impulses” account in a scientific sense for the numerous and beautiful co-adaptations which we see throughout nature; I cannot see that we thus gain any insight how, for instance, a woodpecker has become adapted to its peculiar habits of life. The work, from its powerful and brilliant style, though displaying in the earlier editions little accurate knowledge and a great want of scientific caution, immediately had a very wide circulation. In my opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views. In 1846 the veteran geologist M. J. d’Omalius d’Halloy published in an excellent, though short paper (“Bulletins de l’Acad. Roy. Bruxelles,” tom. xiii, p. 581), his opinion that it is more probable that new species have been produced by descent with modification, than that they have been separately created: the author first promulgated this opinion in 1831.

  Professor Owen, in 1849 (“Nature of Limbs,” p. 86), wrote as follows: —“The archetypal idea was manifested in the flesh under diverse such modifications, upon this planet, long prior to the existence of those animal species that actually exemplify it. To what natural laws or secondary causes the orderly succession and progression of such organic phenomena may have been committed, we, as yet, are ignorant.” In his Address to the British Association, in 1858, he speaks (p. li.) of “the axiom of the continuous operation of creative power, or of the ordained becoming of living things.” Farther on (p. xc.), after referring to geographical distribution, he adds, “These phenomena shake our confidence in the conclusion that the Apteryx of New Zealand and the Red Grouse of England were distinct creations in and for those islands respectively. Always, also, it may be well to bear in mind that by the word ‘creation’ the zoologist means ‘a process he knows not what.’ ” He amplifies this idea by adding, that when such cases as that of the Red Grouse are “enumerated by the zoologist as evidence of distinct creation of the bird in and for such islands, he chiefly expresses that he knows not how the Red Grouse came to be there, and there exclusively; signifying also by this mode of expressing such ignorance his belief, that both the bird and the islands owed their origin to a great first Creative Cause.” If we interpret these sentences given in the same Address, one by the other, it appears that this eminent philosopher felt in 1858 his confidence shaken that the Apteryx and the Red Grouse first appeared in their respective homes, “he knew not how,” or by some process “he knew not what.” Since the publication in 1859 of my work on the “Origin of Species,” but whether in consequence of it is doubtful, Professor Owen has clearly expressed his belief that species have not been separately created, and are not immutable productions; but he still (“Anatomy of the Vertebrates,” 1866) denies that we know the natural laws or secondary causes of the successive appearance of species; yet he at the same time admits that natural selection may have done something towards this end. It is surprising that this admission should not have been made earlier, as Professor Owen now believes that he promulgated the theory of natural selection in a passage read before the Zoological Society in February, 1850 (“Transact.” vol. iv, p. 15); for in a letter to the “London Review” (May 5, 1866, p. 516), commenting on some of the reviewer’s criticisms, he says, “No naturalist can dissent from the truth of your perception of the essential identity of the passage cited with the basis of that [the so-called Darwinian] theory, the power, viz., of species to accommodate themselves, or bow to the influences of surrounding circumstances.” Further on in the same letter he speaks of himself as “the author of the same theory at the earlier date of 1850.” This belief in Professor Owen that he then gave to the world the theory of natural selection will surprise all those who are acquainted with the several passages in his works, reviews, and lectures, published since the “Origin,” in which he strenuously opposes the theory; and it will please all those who are interested on this side of the question, as it may be presumed that his opposition will now cease. It should, however, be stated that the passage above referred to in the “Zoological Transactions,” as I find on consulting it, applies exclusively to the extermination and preservation of animals, and in no way to their gradual modification, origination, or natural selection. So far is this from being the case that Professor Owen actually begins the first of the two paragraphs (vol. iv, p. 15) with the following words: —“We have not a particle of evidence that any species of bird or beast that lived during the pliocene period has had its characters modified in any respect by the influence of time or of change of external circumstances.”

  M. Isidore Geoffroy Saint Hilaire, in his Lectures
delivered in 1850 (of which a Résumé appeared in the “Revue et Mag. de Zoolog.,” Jan. 1851), briefly gives his reason for believing that specific characters “sont fixes, pour chaque espèce, tant qu ’elle se perpétue au milieu des mêmes circonstances: ils se modifient, si les circonstances ambiantes viennent à changer.” “En résumé l’observation des animaux sauvages démontre déjà la variabilité limitée des espèces. Les expériences sur les animaux sauvages devenus domestiques, et sur les animaux domestiques redevenus sauvages, la démontrent plus clairement encore. Ces mêmes expériences prouvent, de plus, que les différences produites peuvent être de valeur générique.” In his “Hist. Nat. Générale” (tom. ii, p. 430, 1859) he amplifies analogous conclusions.

  From a circular lately issued it appears that Dr. Freke, in 1851 (“Dublin Medical Press,” p. 322), propounded the doctrine that all organic beings have descended from one primordial form. His grounds of belief and treatment of the subject are wholly different from mine; but as Dr. Freke has now (1861) published his Essay on “the Origin of Species by means of Organic Affinity,” the difficult attempt to give any idea of his views would be superfluous on my part.

  Mr. Herbert Spencer, in an Essay (originally published in the “Leader,” March 1852, and republished in his “Essays” in 1858), has contrasted the theories of the Creation and the Development of organic beings with remarkable skill and force. He argues from the analogy of domestic productions, from the changes which the embryos of many species undergo, from the difficulty of distinguishing species and varieties, and from the principle of general gradation, that species have been modified; and he attributes the modification to the change of circumstances. The author (1855) has also treated Psychology on the principle of the necessary acquirement of each mental power and capacity by gradation.