486 THE HISTORY OF BIOLOGY 



He established the fact that the western half of the archipelago possesses 

 an essentially Indian animal world, whereas the eastern half has an equally- 

 marked Australian fauna; the border-line he found to lie in the narrow but 

 deep sound between the islands Bali and Lombok, and northwards from there 

 in the Macassar Strait between Borneo and the Celebes. He afterwards com- 

 piled, with the aid of the results gained during this and subsequent voyages, 

 an animal geographical system, in which the globe was divided into sep- 

 arate regions based on the distribution of animal forms both in recent times 

 and in preceding periods. This animal geographical system, which is univer- 

 sally known from the text-books on zoology, is a contribution of lasting 

 value to the development of biology. 



But in the course of his studies of the distribution of animal life in the 

 East Indian islands Wallace found himself faced with the same problems as 

 Darwin in the Galapagos Islands; the various islands and island-groups pos- 

 sess their peculiar animal species. The distribution of species on the earth is 

 thus governed by geological conditions, and if we consider the animal life 

 of earlier periods we find that, instead of the new extant forms, there were 

 other similar forms — in fact, that, as he says, every species has been pre- 

 ceded in time and space by a similar species. These reflections he recorded 

 in a treatise which he sent home and which was printed in 1855. The ex- 

 planation of the phenomenon he found — like Darwin — when meditating 

 upon Malthus's theory of competition; it is the struggle for existence that 

 has compelled living creatures to develop themselves in order not to perish 

 in the struggle against other species; if a variety has been equipped with 

 more powerful qualities than the main species, it drives out the latter and 

 usurps its place. This theory Wallace expounded in a report, which he sent 

 to Darwin for perusal; the latter was struck by the agreement with the 

 ideas that he himself just happened to be working out and found the situa- 

 tion highly embarrassing. At the suggestion of some friends he published 

 Wallace's treatise together with a report of his own results, which he sub- 

 mitted to the Linnean Society in 1858, thus giving science an opportunity 

 of seeing the same theory presented by two investigators working independ- 

 ently. Much surprise has been expressed at the incident, which has often 

 been put forward as a proof of the undeniable truth of the theory. It is pos- 

 sible to find an explanation of the phenomenon by making a comparison 

 between the two originators of the theory; they were both self-taught men 

 with essentially systematic interests, but without any anatomical training; 

 they had both explored an island region and received their impressions there- 

 from; both had consequently been confronted with the problem of the dis- 

 tribution of species, and, finally, both had been influenced by Malthus; and 

 though the fundamental view-point is the same in both scientists, yet Wal- 

 lace has a conception of the problem that is in many respects peculiar to 



