I. Haeckel and His Opponents

The doubt as to the view that there underlies each distinct organic species a special plan of organisation, unchangeable for all time, took firm hold upon Darwin upon a journey which he undertook to South America and Australia in the summer of 1831 as naturalist on the ship Beagle. As to how his thought ripened, we get an idea in reaching such communications from him as the following: “When, during the voyage of the Beagle, I visited the Galapagos Archipelago, which lies in the Pacific Ocean some five hundred English miles from the South American coast, I saw myself surrounded by peculiar kinds of birds, reptiles, and snakes, which exist nowhere else in the world. Yet they almost all bore upon them an American character. In the song of the mocking thrush, in the sharp cry of the carrion hawk, in the great chandelier-like Opuntico, I clearly perceived the neighbourhood of America; and yet these islands were separated from the mainland by so many miles, and differed widely from it in their geological constitution and their climate. Yet more surprising was the fact that most of the inhabitants of each separate island of this small archipelago were specifically different, although closely related to one another. I often asked myself, then, how these peculiar animals and men had originated. The simplest answer seemed to be that the inhabitants of the different islands descend from one another, and in the course of their descent had undergone modifications, and that all the inhabitants of the archipelago had descended from those of the nearest mainland, viz., America, from which naturally the colonisation would proceed. But it long remained for me an unintelligible problem: how the necessary degree of modification could have been attained.”