[1] Origin of Species, p. 367.

[2] Origin of Species, p. 372.

[3] Origin of Species, pp. 368-9.

[4] It is, however, probable that all species of the genus retained a tiny rudiment of wings in greatly dwindled scapulo-coracoid bones. And Mr. H. O. Forbes has detected, in a recently exhumed specimen of the latter, an indication of the glenoid cavity, for the articulation of an extremely aborted humerus. (See Nature, Jan. 14th, 1892.)

[5] See especially Mr. John Wood’s papers, Proc. R. S., xiii to xvi, and xviii; also Journ. Anat., i and iii. In this connexion Darwin refers to M. Richard, Annls. d. Sc. Nat. Zoolg., tom. xviii, p. 13, 1852.

[6] Proc. Nat. Hist. Soc., Boston, 1863.

[7] Nineteenth Century, November, 1891.

[8] Descent of Man, 2nd ed., pp. 15-16.

[9] I say “probably,” because analogy points in this direction. As a matter of fact, in many cases of tissue-formation karyokinesis has not hitherto been detected. But even if in such cases it does not occur—i. e. if failure to detect its occurrence be not due merely to still remaining imperfections of our histological methods,—the large number of cases in which it has been seen to occur in the formation of sundry tissues are of themselves sufficient to indicate some important difference between cells derived from ova (metazoal), and cells which have not been so derived (protozoal). Which is the point now under discussion.

[10] Even when propagated by budding, a multicellular organism has been ultimately derived from a germ-cell.

[11] It has already been stated that both parthenogenesis and gemmation are ultimately derived from sexual reproduction. It may now be added, on the other hand, that the earlier stages of parthenogenesis have been observed to occur sporadically in all sub-kingdoms of the Metaxoa, including the Vertebrata, and even the highest class, Mammalia. These earlier stages consist in spontaneous segmentations of the ovum; so that even if a virgin has ever conceived and borne a son, and even if such a fact in the human species has been unique, still it would not betoken any breach of physiological continuity. Indeed, according to Weismann’s not improbable hypothesis touching the physiological meaning of polar bodies, such a fact need betoken nothing more than a slight disturbance of the complex machinery of ovulation, on account of which the ovum failed to eliminate from its substance an almost inconceivably minute portion of its nucleus.

[12] The spermatozooids of certain plants can be strongly attracted towards a pipette which is filled with malic acid—crowding around and into it with avidity.

[13] Ray Lankester, Encyclop. Brit., 9th ed., Vol. XIX, pp. 832-3.

[14] In most vertebrated animals this process of gastrulation has been more or less superseded by another, which is called delamination; but it scarcely seems necessary for our present purposes to describe the latter. For not only does it eventually lead to the same result as gastrulation—i. e. the converting of the ovum into a double-walled sac,—but there is good evidence among the lower Vertebrata of its being preceded by gastrulation; so that, even as to the higher Vertebrata, embryologists are pretty well agreed that delamination has been but a later development of, or possibly improvement upon, gastrulation.

[15] The most extreme of them is that which is mentioned in the last foot-note.

[16] For objections which may be brought against this and similar statements, see the Appendix.

[17] For difficulties and objections, see Appendix.

[18] Heilprin, Geological Evidences of Evolution, pp. 73-4 (1888).

[19] Le Conte, loc. cit., pp. 236-7.

[20] I say “large areas” for the sake of argument; but the same correlation between distribution and affinity extends likewise to small areas where only small differences of affinity are concerned. Thus, for instance, speaking of smaller areas, Moritz Wagner says:—"The broader and more rapid the river, the higher and more regular the mountain-chain, the calmer and more extensive the sea, the more considerable, as a general rule, will be the taxonomic separation between the populations"; and he shows that, in correlation with such differences in the degrees of separation, are the degrees of diversification—i. e., the numbers of species, and even of varieties, which these topographical barriers determine.

[21] The only exception is in the case of the fish on each side of the Isthmus of Panama, where about 30 per cent, of the species are identical. But it is possible enough that at some previous time this narrow Isthmus may have been even narrower than at present, if not actually open. At all events, the fact that this partial exception occurs just where the land-barrier is so narrow, is more suggestive of migration than of independent creation.

[22] Origin of Species, pp. 353-4.

[23] Wallace, Island Life, pp. 271-2.

[24] Wallace, Island Life, p. 287.

[25] Wallace, Island Life, p. 287.

[26] For quotations, see Note A.

[27] Whewell, Indications of the Creator, 2nd ed., 1846.

[28] De Blainville, Compte Rendu, 1837.

[29] Whewell, ibid., p. 162.

[30] For cases, see Animal Intelligence, in the chapters on Ants and Bees; and, for discussion of principles, Mental Evolution in Animals, in the chapters on Instinct.

[31] Prince Kropotkin in the Nineteenth Century (Feb. 1888, Apr. 1891) has adduced a large and interesting body of facts, showing the great prevalence of the principle of co-operation in organic nature.

[32] Darwinism, pp. 218 and 227.

[33] Since the above was written Prof. Lloyd Morgan has published a closely similar notice of the passage in question. “This language,” he says, “seems to savour of teleology (that pitfall of the evolutionist). The cart is put before the horse. The recognition-marks were, I believe, not produced to prevent intercrossing, but intercrossing has been prevented because of preferential mating between individuals possessing special recognition-marks. To miss this point is to miss an important segregation-factor."—(Animal Life and Intelligence, p. 103.) Again, on pp. 184-9, he furnishes an excellent discussion on the whole subject of the fallacy alluded to in the text, and gives illustrative quotations from other prominent Darwinians. I should like to add that Darwin himself has nowhere fallen into this, or any of the other fallacies, which are mentioned in the text.

[34] Of course adaptive modifications produced in the individual lifetime, and not inherited, do not concern the question at all. In this and the following paragraphs, therefore, “adaptations,” “adaptive modifications,” &c., refer exclusively to such as are hereditary, i. e. phyletic.

[35] The question as to whether natural selection has been the only principle concerned in the origination of species, is quite distinct from that as to the accuracy of the above definition.

[36] It is often objected to Darwin’s terminology, that it embraces such words as “contrivance,” “purpose,” &c., which are strictly applicable only to the processes or the products of thought. But when it is understood that they are used in a neutral or metaphorical sense, I cannot see that any harm arises from their use.

[37] Note B.

[38] Were it not that some of Darwin’s critics have overlooked the very point wherein the great value of protective colouring as evidence of natural selection consists, it would be needless to observe that it does so in the minuteness of the protective resemblance which in so many cases is presented. Of course where the resemblance is only very general, the phenomena might be ascribed to mere coincidence, of which the instincts of the animal have taken advantage. But in the measure that the resemblance becomes minutely detailed, the supposition of mere coincidence is excluded, and the agency of some specially adaptive cause demonstrated. Again, it is almost needless to say, no real difficulty is presented (as has been alleged) by the cases above quoted of seasonal imitations, on the ground that natural selection could not act alternately on the same individual. Natural selection is not supposed to act alternately on the same individual. It is supposed to act always in the same manner, and if, as in the case of a regularly recurring change in the colours of the environment, correspondingly recurrent changes are required to appear in the colours of the animals, natural selection sets its premium upon those individuals the constitutions of which best lend themselves to seasonal changes of the needful kind—probably under the influence of stimuli supplied by the changes of external conditions (temperature, moisture, &c.).

[39] For a full account of this instinct and its probable purpose, see Animal Intelligence, pp. 93-6.

[40] Both drawings are reproduced from Mr. Poulton’s paper upon the subject (Proc. Zool. Soc., June 16, 1891).

[41] Anatomy of Vertebrates, vol. iii. p. 794.

[42] The degree in which variability is indefinite, or, on the contrary, determinate, is a question which is not yet ripe for decision—nor even, in my opinion, for discussion. But I may here state the following general principles with regard to it.

(1) It is evident that up to some point or another variations must be pre-determined in definite lines. Men do not gather grapes from thorns, figs from thistles, nor even moss-roses from sweet-briars. In other words, “the nature of the organism” in all cases necessitates the limiting of variations within certain bounds.

(2) But when the question is as to what these bounds may be, we can only answer in a general way that, according to the general theory of evolution, they must be such as are imposed by heredity, coupled with the degree to which external conditions of life (and possibly also use-inheritance) are capable, in given cases, of modifying congenital characters. These are the only causes which the theory of descent can consistently recognise as producing variations in determinate directions.

(3) Inasmuch as variation presupposes the existence of parts that vary, and inasmuch as the variation of parts can only be in the alternative directions of increase or decrease around an average, it follows that, in the first instance at all events, every variation, if determinate, must be so only in one or other of these two opposite directions.

(4) In as far as variations are summated in successive generations, so as eventually to give rise to new structures, organs, mechanisms, &c., natural selection is theoretically competent to explain the facts, without our having to postulate the operation of unknown causes producing variations in determinate lines,—or not further than is stated in paragraphs 1 and 2.

(5) Nevertheless, it does not follow that there are not such other unknown causes; and, if there are, of course the importance of natural selection as a cause of adaptive modification would be limited in proportion to their number and the extent of their operation. But it is for those who, like the late Professors Asa Gray and NÄgeli, maintain the existence of such causes, to substantiate their belief by indicating them.

[43] Within the last few months this objection has been presented anew by Mr. D. Syme, whose book On the Modification of Organisms exhibits a curious combination of shrewd criticisms with almost ludicrous misunderstandings. One of the latter it is necessary to state, because it pervades the quotation which I am about to supply. He everywhere compares “natural selection” with “the struggle for existence,” uses them as convertible terms, and while absurdly stating that “Darwin defines natural selection as the struggle for existence,” complains of “the liability of error, both on his own part and on the part of his readers,” which arises from his not having everywhere adhered to this definition! (p. 8).

“Darwin has put forth two distinct and contradictory theories of the functions of natural selection. According to the one theory natural selection is selective or preservative, and nothing more. According to the other theory natural selection creates the variations(!) ... It certainly seems absurd to speak of natural selection, or the struggle for existence, as selective or preservative, for the struggle for existence does not preserve at all, not even the fit variations, as both the fit and the unfit struggle for existence, the unfit naturally more than the fit, and the fit are preserved, not in consequence of the struggle, but in consequence of their fitness. Suppose two varieties of the same species are driven, by an increase of their numbers, to seek for subsistence in a colder region than they have been accustomed to, and that one of these varieties had a hardier constitution than the other; and let us suppose that the former withstood the severe climate better than the latter, and consequently survived, while the other perished. In this case the hardier survived, not because of the struggle, but because it had a constitution better adapted to the climate. I wish to ascertain if a certain metal in my possession is gold or some baser metal, and I apply the usual test; but the mere fact of my testing this metal would not make it gold or any other kind of metal.”

I have thought it worth while to quote this passage for the sake of showing the extraordinary confusion of mind which still prevails on the part of Darwin’s critics, even with reference to the very fundamental parts of his theory. For, as I have said, the writer of this passage shows himself a shrewd critic in some other parts of his essay, where he is not engaged especially on the theory of natural selection.

[44] Principles of Geology, vol. ii. p. 487 (11th ed.).

[45] Syme, on the Modification of Organisms, p. 46.

[46] Variation of Plants and Animals, vol. ii. p. 315.

[47] The chambers are three in number. The two upper ones are occupied respectively by the male and the sitting female. The lower one serves as a general living room when the young are hatched.

[48] Note C.

[49] Since the above exposition of the theory of sexual selection was written, Mr. Poulton has published his work on the Colours of Animals. He there reproduces some of the illustrations which occur in Mr. and Mrs. Peckham’s work on Sexual Selection in Spiders, and furnishes appropriate descriptions. Therefore, while retaining the illustrations, I have withdrawn my own descriptions.

Mr. Poulton has also in his book supplied a rÉsumÉ of the arguments for and against the theory of sexual selection in general. Of course in nearly all respects this corresponds with the rÉsumÉ which is given in the foregoing pages; but I have left the latter as it was originally written, because all the critical part is reproduced verbatim from a review of Mr. Wallace’s Darwinism, of a date still earlier than that of Mr. Poulton’s book—viz. Contemporary Review, August, 1889.

[50] The beauty of autumnal tints in fading leaves may possibly be adduced per contra. But here we have to remember that it is only some kinds of leaves which thus become beautiful when fading, while, even as regards those that do, it is not remarkable that their chlorophyll should, as it were, accidentally assume brilliant tints while breaking down into lower grades of chemical constitution. The case, in fact, is exactly parallel to those in the animal kingdom which are considered in the ensuing paragraphs.

[51] The best treatise on this subject is Prof. Le Conte’s Evolution and its Relation to Religious Thought (Appleton & Co. 1888).

[52] See Mental Evolution in Animals, pp. 110-111.

[53] Origin of Species, 282-5.

[54] Elements of Geology, p. 587.

[55] Origin of Species, p. 289.

[56] Ibid.

[57] See Lay Sermons, Lecture on Geological Reform.

[58] See especially the following Presidential addresses:—Geol. Assoc. Nov. 1876; Section D. Brit. Assoc., 1886; Lin. Soc., 1890.

[59] Elements of Geology, p. 280.

[60] Origin of Species, p. 332.

[61] Origin of Species, p. 332.

[62] Ibid. pp. 333-4.

[63] Evolution and its Relation to Religious Thought, p. 194.

[64] On Truth, p. 493.

[65] Nature, vol. xli, p. 344.

[66] Entomologist, March, 1890.

[67] Nature, vol. xli, p. 394.

[68] Ibid. vol. xli, pp. 559-560.