CHAP. XVII The Evidences of Evolution 275 



of the world. To the statements of the case by Spencer, 

 Haeckel, Huxley, Romanes, and others, I have given 

 references in the chapter on books. Darwin's arguments 

 were derived («) from the distribution of animals in space ; 

 {p) from their successive appearance in time, {c) from actual 

 variations observed in domestication, cultivation, and in 

 nature ; {d) from facts of structure, e.g. homologous and 

 rudimentary organs, {e) from embryology. I shall simply 

 illustrate the different kinds of evidence, and that under 

 three heads — {a) physiological, {b) structural, {c) his- 

 torical. 



(a) Physiological. — A study of the life of organisms 

 shows that the ancient and even Linncsan dogma of the 

 constancy or immutability of species was false. Organisms 

 change under our eyes. They are not like cast-iron ; they 

 are plastic. One of the most striking cases in the Natural 

 History Collection of the British Museum is that near the 

 entrance, where on a tree are perched domesticated pigeons 

 of many sorts — fantail, pouter, tumbler, and the like — 

 while in the centre is the ancestral rock-dove Columba livia, 

 from which we know that all the rest have been derived. 

 In other domesticated animals, even when we allow that 

 some of them have had multiple origins, we find abundant 

 proof of variability. But what occurs under man's super- 

 vision in the domestication of animals and in the culti- 

 vation of plants occurs also in the state of nature. Natural 

 " varieties " which Hnk species to species are very common, 

 and the offspring of one brood differ from one another and 

 from their parents. How many strange sports there are 

 and grim reversions ! and, as we shall afterwards see, 

 modifications of individuals by force of external conditions 

 are not uncommon. Those who say they see no variation 

 now going on in nature should try a month's work at identi- 

 fying species. I have known of an ancient man who dwelt 

 in a small town ; he did not believe in the reality of railways 

 and to him the testimony of observers was as an idle tale ; 

 he was not daunted in his scepticism even when the railway 

 was extended to his town, for he was aged, and remained 

 at home, dying a professed unbeliever in that which he had 



