604 SPECIAL METHODS OF DISCOVERY. 



manner in which closely allied species replace species 

 in going southward. Secondly, the close affinity of the 

 species inhabiting the islands near South America to those 

 proper to the continent. This struck me profoundly, 

 especially the difference of the species in the adjoining 

 islets in the Gralapagos Archipelago. Thirdly, the rela- 

 tion of the living edentata and rodentia to the extinct 

 species. I shall never forget my astonishment when I 

 dug out a gigantic piece of armour like that of the living 

 armadillo.' 'Eeflecting on these facts, and collecting 

 analogous ones, it seemed to me probable that allied 

 species were descended from a common parent. But for 

 some years I could not conceive how each form became so 

 excellently adapted to its habits of life. I then began 

 systematically to study domestic productions, and, after a 

 time, saw clearly that man's selective power was the most 

 important agent. I was prepared, from having studied 

 the habits of animals, to appreciate the struggle for 

 existence, and my work in geology gave me some idea 

 of the lapse of past time. Therefore when I happened to 

 read " Malthus on Population," the idea of natural selec- 

 tion flashed on me. Of all the minor points, the last 

 which I appreciated was the importance and cause of the 

 principle of divergence.' 1 It was by means of extensive 

 knowledge, study, and inference that Darwin (and also 

 Wallace) discovered the foregoing theory. Haeckel. by 

 a similar process of inference, has drawn the conclusion 

 that the ' Olynthus calcareous sponge ' is one of the most 

 ancient and important ancestors of the human race, 2 and 

 that all the calcareous sponges are derived from it. 



No supernatural theory, or assumption of the operation 

 of occult causes, can as completely explain organic deve- 

 lopment, or the conditions of evolution of man, as that of 

 1 Haeckel, History of Creation, vol. i. p. 134. 2 Ibid. p. 16. 



