the idea involved is not entirely unqualified, as is shown by the following significant statement: On the theory of natural selection we can clearly understand the full meaning of the old canon in natural history, "Natura non facit saltum." This canon, if we look to the present inhabitants alone of the world, is not strictly correct; but if we include all those of past times, whether known or unknown, it must on this theory be strictly true." This I understand to be in effect a protest against deducing proof of separate creations from the imperfection of the geological record, coupled with an admission that saltation or mutation does, at least occasionally, occur among existing living forms. I trust you perceive the importance of the concession that natura non facit saltum is not strictly correct as applied to the present inhabitants of the world. Having noticed Mr. Darwin's repeated use of the words per saltum, I now wish to revert to his frequent use of the words monster and monstrosity and to call your attention to the fact that they are not always employed with exactly the same meanings. Sometimes by "monstrosity" he evidently intends to indicate a mere deformity of the nature of an accidental injury, or aborted or perverted development, but more generally he refers to a deviation from type wide enough, or discontinuous enough, to exclude it from the category of variations. to which he supposed the operation of natural selection must be confined. Among domesticated animals and plants, however, the word monster as used by him often meant no more than the word "sport." In most cases when he used this term or one of its derivatives he took care to explain that monstrosities could not be qualitatively separated from other kinds of variations. Thus, in writing to R. Meldola, in 1873, he says: It is very difficult or impossible to define what is meant by a large variation. Such graduate into monstrosities or generally injurious variations. I do not myself believe that these are often or ever taken advantage of under nature." 25Origin of Species,'' 6th ed., See also ibid., pp. 156, 234, 414. In the "Origin of Species" he wrote: At long intervals of time, out of millions of individuals reared in the same country and fed on nearly the same food, deviations of structure so strongly pronounced as to deserve to be called monstrosities arise; but monstrosities cannot be separated by any distinct line from slighter variations." He frequently repeats this statement and it is quite clear that he intends to convey the idea that all variations are merely quantitative; at any rate he failed to adopt a nomenclature that would enable his readers to judge as to the degrees of difference he meant to indicate by such adjectives as "insensible," "minute,' "slight," "large," "wide," "sudden" and "abrupt," as applied to variations. I am convinced, however, that he had in mind an idea that there were two different kinds of variations, namely, first, what he oftenest called “individual variations," by which he referred to the ordinary differences between the single organisms of the same group, or what mutationists now call "fluctuations,' and, second, those radical and generally extensive deviations from type which constitute an actual break with the species, variety or race, and which are substantially what we of these later times have named "mutations." There are places in Darwin's works where the two kinds of variation just mentioned are spoken of as "indefinite" and definite" and as results, respectively, of the indirect and the direct action of the conditions of life, and once only, I think, he uses the term "fluctuating variability" as synonymous with indefinite variability.28 variability.28 Now I do not assume to say that the recognition of these distinctions by Mr. Darwin proves that he clearly foresaw the present-day mutation theory with its foundation in the principle of unit characters, but I think it is true that he had at least a glimpse of the coming modifications *Origin of Species," 6th ed., p. 6, also p. 33. See also "Animals and Plants Under Domestication," 2d ed., Vol. I, pp. 312, 322. "More Letters," 1903, Vol. I, p. 318. Also Animals and Plants Under Domestication," 2d ed., Vol. II, PP. 280, 281, 345. to be required in his own theory to meet the then dawning truth. De Vries declares that his own field researches and testing of native plants are based "on the hypothesis of unit-characters as deduced from Darwin's Pangenesis," which conception, De Vries points out, “led to the expectation of two different kinds of variability, one slow and one sudden.''29 But the main point I wish to dwell upon at present is that Darwin recognized, at least dimly, a kind of variability the results of which were essentially different from the "individual" or "indefinite" variations, which mistakenly seemed to him alone capable of being acted upon by selection. He was sorely puzzled by what he saw and realized in this direction, for he had spent more than twenty years of intense thought in elaborating his theory that new species were evolved from older ones by the gradual building up of new characters from extremely small differences, and he feared that the admission of saltation in any form meant the undermining of the foundations he had labored so hard to construct. He had once said: When we remember such cases as the formation of the more complex galls, and certain monstrosities, which cannot be accounted for by reversion, cohesion, &c., and sudden strongly-marked deviations of structure, such as the appearance of a moss-rose on a common rose, we must admit that the organization of the individual is capable through its own laws of growth, under certain conditions, of undergoing great modifications, independently of the gradual accumulation of slight inherited modifications.30 In the last edition of the "Origin of Species," however, which was published in the year of the author's death, although he introduces this apology: "In the earlier editions of this work I underrated, as it now seems probable, the frequency and importance of modifications due to spontaneous variability," he still later inter"Species and Varieties, their Origin by Mutation," 2d ed., 1906, p. 689. 2966 30Origin of Species," 5th ed., 1869, polates the following rather sweeping recantation: There are, however, some who still think that species have suddenly given birth, through quite unexplained means, to new and totally different forms; but, as I have attempted to show, weighty evidence can be opposed to the admission of great and abrupt modifications. Under a scientific point of view, and as leading to further investigation, but little advantage is gained by believing that new forms are suddenly developed in an inexplicable manner from old and widely different forms, the old belief in the creation of species from the dust of the over In this sixth, and last, edition of the "Origin of Species" Mr. Darwin devotes to the task of answering criticisms made by St. George Mivart far more space than he had ever allowed to any other one critic and the passage just read is evidently one of those inspired by Mr. Mivart's attacks. The sore point with Mr. Darwin at that time was the doctrine of natural selection and, as I have already remarked, he had adopted the erroneous belief that this important principle must be greatly weakened if not entirely sacrificed if any form of saltation was to be admitted in nature. He had, therefore, wavered between his loyalty to his cherished hypothesis and his fearless devotion to truth. By this time, however, he had so long contemplated the possibility of the origin of new species and varieties through single long steps and had had so many convincing examples brought to his attention, that his hesitancy and doubt concerning the validity and sufficiency of the arguments urged in favor of this mode of evolution were ready to give way, and I regard the passage, which I am about to quote, as a virtual surrender on this point. The fact that, in this emphatic form, it was written at the close of his life, as his last word on this subject, and that he must have felt contained a concession very damaging to the that it theory to the establishment of which that life had been devoted, gives it, in my mind, a deeply pathetic signifi cance. 3266 Mr. Darwin says: Origin of Species," 6th ed., 1882, p. 424. It appears that I formerly underrated the frequency and value of [variations which seem to us in our ignorance to arise spontaneously] as leading to permanent modifications of structure independently of natural selection. But as my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position-namely, at the close of the Introduction the following words: "I am convinced that natural selection has been the main but not the exclusive means of modification." This has been of no avail. Great is the power of steady misrepresentation; but the history of science shows that this power does not long endure.33 The sting of this vehement declaration is in the underlying implication that the limitation placed upon the applicability of natural selection was deemed necessary because of Mr. Darwin's inability to free his mind from the belief that it could not act upon large and sudden variations as well as upon small and unimportant ones. This point of view seems illogical when we consider his repeated declaration that no qualitative distinction could be established between the two kinds of variation, but it may be partially accounted for by the fact that a slight confusion at times existed in his mind concerning the general modus operandi of natural selection, through which he attributed to it a causal power as well as a mere sifting effect. Both Lyell and Wallace took him to task for this double use of the term and, therefore, in the third edition of "the Origin" he attempted to clear up this point by means of this statement: Several writers have misapprehended or objected to the term natural selection. Some have even imagined that natural selection even induces variability, whereas it implies only the preservation of such variations. as arise and are beneficial to the being under its conditions of life." Nevertheless, almost side by side with this explanation we find in the last edition of "the Origin," the following sentences which were allowed to come down from the first edition: "Natural Selection will modify the 33Origin of Species,' 6th ed., p. 421. See also, Life and Letters," 1886, Vol. III, p. 243, and More Letters," 1907, Vol. I, p. 389. 34 Origin of Species,'' 3d ed., 1861, p. 84. |