A similar line of reasoning is as applicable to separate organs as to the whole organisation. A writer[91] has recently maintained that “it is probably no exaggeration to suppose that in order to improve such an organ as the eye at all, it must be improved in ten different ways at once. And the improbability of any complex organ being produced and brought to perfection in any such way is an improbability of the same kind and degree as that of producing a poem or a mathematical demonstration by throwing letters at random on a table.” If the eye were abruptly and greatly modified, no doubt many parts would have to be simultaneously altered, in order that the organ should remain serviceable.
But is this the case with smaller changes? There are persons who can see distinctly only in a dull light, and this condition depends, I believe, on the abnormal sensitiveness of the retina, and is known to be inherited. Now if a bird, for instance, receive some great advantage from seeing well in the twilight, all the individuals with the most sensitive retina would succeed best and be the most likely to survive; and why should not all those which happened to have the eye itself a little larger, or the pupil capable of greater dilatation, be likewise preserved, whether or not these modifications were strictly simultaneous? These individuals would subsequently intercross and blend their respective advantages. By such slight successive changes, the eye of a diurnal bird would be brought into the condition of that of an owl, which has often been advanced as an excellent instance of adaptation. Short-sight, which is often inherited, permits a person to see distinctly a minute object at so near a distance that it would be indistinct to ordinary eyes; and here we have a capacity which might be serviceable under certain conditions, abruptly gained. The Fuegians on board the Beagle could certainly see distant objects more distinctly than our sailors with all their long practice; I do not know whether this depends upon sensitiveness or on the power of adjustment in the focus; but this capacity for distant vision might, it is probable, be slightly augmented by successive modifications of either kind. Amphibious animals which are enabled to see both in the water and in the air, require and possess, as M. Plateau has shown,[92] eyes constructed on the following plan: “the cornea is always flat, or at least much flattened in the front of the crystalline and over a space equal to the diameter of that lens, whilst the lateral portions may be much curved.” The crystalline is very nearly a sphere, and the humours have nearly the same density as water. Now as a terrestrial animal became more and more aquatic in its habits, very slight changes, first in the curvature of the cornea or crystalline, and then in the density of the humours, or conversely, might successively occur, and would be advantageous to the animal whilst under water, without serious detriment to its power of vision in the air. It is of course impossible to conjecture by what steps the fundamental structure of the eye in the Vertebrata was originally acquired, for we know nothing about this organ in the first progenitors of the class. With respect to the lowest animals in the scale, the transitional states through which the eye at first probably passed, can by the aid of analogy be indicated, as I have attempted to show in my ‘Origin of Species.’[93]
REFERENCES
[1] The term unconscious selection has been objected to as a contradiction; but see some excellent observations on this head by Prof. Huxley (‘Nat. Hist. Review,’ Oct. 1864, p. 578), who remarks that when the wind heaps up sand-dunes it sifts and unconsciously selects from the gravel on the beach grains of sand of equal size.
[2] ‘On Sheep,’ 1838, p. 60.
[3] Mr. J. Wright on Shorthorn Cattle, in ‘Journal of Royal Agricult. Soc.,’ vol. vii. pp. 208, 209.
[4] H. D. Richardson ‘On Pigs,’ 1847, p. 44.
[5] ‘Journal of Royal Agricult. Soc.,’ vol. i. p. 24.
[6] ‘On Sheep,’ pp. 520, 319.
[7] Loudon’s ‘Mag. of Nat. Hist.,’ vol. viii., 1835, p. 618.
[8] ‘A treatise on the Art of Breeding the Almond Tumbler.’ 1851. p. 9.
[9] ‘Recreations in Agriculture,’ vol. ii. p. 409.
[10] Youatt on Cattle, pp. 191, 227.
[11] Ferguson, ‘Prize Poultry,’ 1854, p. 208.
[12] Wilson, in ‘Transact. Highland Agricult. Soc.,’ quoted in ‘Gardener’s Chronicle,’ 1844, p. 29.
[13] Simmonds, quoted in ‘Gardener’s Chronicle,’ 1855, p. 637. And for the second quotation, see Youatt on Sheep, p. 171.
[14] Robinet, ‘Vers à Soie,’ 1848, p. 271.
[15] Quatrefages, ‘Les Maladies du Ver à Soie,’ 1859, p. 101.
[16] M. Simon, in ‘Bull. de la Soc. d’Acclimat.,’ tom. ix., 1862, p. 221.
[17] ‘The Poultry Chronicle,’ vol. i., 1854, p. 607.
[18] J. M. Eaton, ‘A Treatise on Fancy Pigeons,’ 1852, p. xiv., and ‘A Treatise on the Almond Tumbler,’ 1851, p. 11.
[19] ‘Journal Royal Agricultural Soc.,’ vol. vi., p. 22.
[20] ‘Poultry Chronicle,’ vol. ii., 1855, p. 596.
[21] Isid. Geoffroy St.-Hilaire, ‘Hist. Nat. Gén.,’ tom. iii. p. 254.
[22] ‘Gardener’s Chronicle,’ 1850, p. 198.
[23] ‘Transact. Hort. Soc.,’ vol. vi. p. 152.
[24] ‘Journal of Horticulture,’ 1862, p. 369.
[25] ‘Transact. Hort. Soc.,’ vol. iv. p. 381.
[26] ‘Transact. Hort. Soc.,’ vol. iv. p. 285.
[27] Rev. W. Bromehead, in ‘Gardener’s Chronicle,’ 1857, p. 550.
[28] ‘Gardener’s Chronicle,’ 1862, p. 721.
29[] Dr. Anderson, in ‘The Bee,’ vol. vi. p. 96; Mr. Barnes in ‘Gardener’s Chronicle,’ 1844, p. 476.
[30] Godron, ‘De l’Espèce,’ 1859, tom. ii. p. 69; ‘Gardener’s Chronicle,’ 1854, p. 258.
[31] On Sheep, p. 18.
[32] Volz, ‘Beiträge zur Kulturgeschichte,’ 1852, s. 47.
[33] Mitford’s ‘History of Greece,’ vol. i. p. 73.
[34] Dr. Dally, translated in ‘Anthropological Review,’ May 1864, p. 101.
[35] Volz, ‘Beiträge,’ etc., 1852, s. 80.
[36] ‘History of the World,’ ch. 45.
[37] ‘Gardener’s Chronicle,’ 1848, p. 323.
[38] Reynier, ‘De l’Économie des Celtes,’ 1818, pp. 487, 503.
[39] Le Couteur on Wheat, p. 15.
[40] Michel, ‘Des Haras,’ 1861, p. 84.
[41] Sir W. Wilde, an ‘Essay on Unmanufactured Animal Remains,’ etc., 1860, p. 11.
[42] Col. Hamilton Smith, ‘Nat. Library,’ vol. xii., Horses, pp. 135, 140.
[43] Michel, ‘Des Haras,’ p. 90.
[44] Mr. Baker, ‘History of the Horse,’ ‘Veterinary,’ vol. xiii. p. 423.
[45] M. l’Abbé Carlier, in ‘Journal de Physique,’ vol. xxiv., 1784, p. 181; this memoir contains much information on the ancient selection of sheep; and is my authority for rams not being killed young in England.
[46] ‘Gardener’s Chronicle,’ 1843, p. 389.
[47] ‘Communications to Board of Agriculture’ quoted in Dr. Darwin’s ‘Phytologia,’ 1800, p. 451.
[48] ‘Mémoire sur les Chinois,’ 1786, tom. xi. p. 55; tom. v. p. 507.
[49] ‘Recherches sur l’Agriculture des Chinois,’ par L. D’Hervey Saint-Denys, 1850, p. 229. With respect to Khang-hi see Huc’s ‘Chinese Empire,’ p. 311.
[50] Anderson, in ‘Linn. Transact.,’ vol. xii. p. 253.
[51] ‘Mém. de l’Acad.’ (divers savants), tom. vi., 1835, p. 333.
[52] ‘Des Quadrupèdes du Paraguay,’ 1801, tom. ii. pp. 333, 371.
[53] ‘The Great Sahara,’ by the Rev. H. B. Tristram, 1860, p. 238.
[54] Pallas, ‘Act. Acad. St. Petersburg,’ 1777, p. 249; Moorcroft and Trebeck, ‘Travels in the Himalayan Provinces,’ 1841.
[55] Quoted from Raffles, in the ‘Indian Field,’ 1859, p. 196: for Varro, see Pallas ut supra.
[56] Erman’s ‘Travels in Siberia,’ Eng. translat., vol. i. p. 453.
[57] See also ‘Journal of R. Geograph. Soc.,’ vol. xiii. part i. p. 65.
[58] Livingstone’s ‘First Travels,’ pp. 191, 439, 565; see also ‘Expedition to the Zambesi,’ 1865, p. 495, for an analogous case respecting a good breed of goats.
[59] Andersson’s ‘Travels in South Africa,’ pp. 232, 318, 319.
[60] Dr. Vavasseur, in ‘Bull. de La Soc. d’Acclimat.,’ tom. viii. 1861, p. 136.
[61] ‘The Natural History of Dee Side,’ 1855, p. 476.
[62] ‘Bull. de la Soc. d’Acclimat.,’ tom. vii. 1860, p. 457.
[63] ‘Cattle,’ p. 48.
[64] Livingstone’s Travels, p. 576; Andersson, ‘Lake Ngami,’ 1856, p. 222. With respect to the sale in Kaffraria, see ‘Quarterly Review,’ 1860, p. 139.
[65] ‘Mémoire sur les Chinois’ (by the Jesuits), 1786, tom. xi. p. 57.
[66] F. Michel, ‘Des Haras,’ pp. 47, 50.
[67] Col. Hamilton Smith, Dogs, in ‘Nat. Lib.,’ vol. x. p. 103.
[68] Azara, ‘Quadrupèdes du Paraguay,’ tom. ii. p. 324.
[69] Sidney’s edit. of Youatt, 1860, pp. 24, 25.
[70] ‘Rural Economy of Yorkshire,’ vol. ii. p. 182.
[71] Moll et Gayot, ‘Du Boeuf,’ 1860, p. 547.
[72] ‘The India Sporting Review,’ vol. ii. p. 181; ‘The Stud Farm,’ by Cecil, p. 58.
[73] ‘The Horse,’ p. 22.
[74] ‘History of England,’ vol. i. p. 316.
[75] ‘Ueber Beständigkeit der Arten.’
[76] Youatt on Sheep, p. 315.
[77] ‘Ueber Shorthorn Rindvieh,’ 1857, s. 51.
[78] Low, ‘Domesticated Animals,’ 1845, p. 363.
[79] ‘Quarterly Review,’ 1849, p. 392.
[80] H. von Nathusius, ‘Vorstudien . . . Schweineschädel,’ 1864, s 140.
[81] See also Dr. Christ, in Rütimeyer’s ‘Pfahlbauten,’ 1861, s. 226.
[82] The passage is given, ‘Bull. Soc. d’Acclimat.,’ 1858, p. 11.
[83] ‘Journal of Horticulture,’ 1862, p. 394.
[84] ‘Gardener’s Chronicle,’ 1857, p. 85.
[85] See Mr. Wildman’s address to the Floricult. Soc. in ‘Gardener’s Chronicle,’ 1843, p. 86.
[86] ‘Journal of Horticulture,’ Oct. 24th, 1865, p. 239.
[87] Prescott’s ‘Hist. of Mexico,’ vol. ii. p. 61.
[88] Sagaret, ‘Pomologie Physiologique,’ 1830, p. 47; Gallesio, ‘Teoria della Riproduzione,’ 1816, p. 88; Godron, ‘De l’Espèce,’ 1859, tom. 2 pp. 63, 67, 70. In my tenth and eleventh chapters I have given details on the potato; and I can confirm similar remarks with respect to the onion. I have also shown how far Naudin concurs in regard to the varieties of the melon.
[89] Godron, ‘De l’Espèce,’ tom. ii. p. 27.
[90] ‘The Anthropological Treatises of Blumenbach,’ 1856, p. 292.
[91] Mr. J. J. Murphy, in his opening address to the Belfast Nat. Hist. Soc., as given in the ‘Belfast Northern Whig,’ Nov. 19th, 1866. Mr. Murphy here follows the line of argument against my views previously and more cautiously given by the Rev. C. Pritchard, Pres. Royal Astronomical Soc., in his sermon (Appendix, p. 33) preached before the British Association at Nottingham, 1866.
[92] On the Vision of Fishes and Amphibia, translated in ‘Annals and Mag. of Nat. Hist.,’ vol. xviii., 1866, p. 469.
[93] Sixth edition, 1872, p. 144.