MODERN BIOLOGY 471 



the ability of his theory, once advanced, to explain practically any biologi- 

 cal phenomena whatsoever, is bound to lead to far-reaching conclusions. 

 Another result of the selection theory is the constant reference to the greatest 

 possible adaptability to prevailing conditions, with the consequent insist- 

 ence upon the finality existing in nature. It has already been pointed out how 

 unsatisfactory this explanation of nature is and further reference will be 

 made to it later on; here it need only be observed that this belief in a pur- 

 poseful adaptability to prevailing conditions has in no small degree contrib- 

 uted towards retarding the development of biology into an exact science. 



The influence that Darwin's Origin of Species exercised will be described 

 in the following. His fame in no wise induced the author to rest on his 

 laurels; on the contrary, he laboured indefatigably throughout his life still 

 further to develop the theory that he had created and to apply it to different 

 life-phenomena. The greatest and most important of his subsequent works 

 was published in 1868 in two volumes and bore the title Animals and Plants 

 under Domestication. In the first volume he gives a detailed account of his 

 intensive racial-biological studies of domestic animals and cultivated plants. 

 The systematic biology of preceding ages had, as a general rule, depreciated 

 these beings: they were not true species, only a medley of varieties that no 

 one could make anything of. Darwin then showed how great is the interest 

 that this racial research possesses and what important results can be pro- 

 duced from it. All later racial research is, in fact, based on his initiative. In 

 point of exactness these investigations of Darwin's certainly cannot be com- 

 pared with those carried out concurrently by Mendel, but they are far more 

 many-sided, as regards both material and conclusions, and they also caused 

 an immense sensation, especially amongst those who led a practical life. 

 Darwin himself largely had recourse to data provided by animal-breeders 

 and gardening experts, and he was certainly not very particular about weed- 

 ing out their alleged results. In the second part of this work he makes fresh 

 contributions to his descent theory. Here he dilates at length upon his con- 

 ception of heredity, which played such a radical part in the cultural history 

 of the nineteenth century, although it is now entirely abandoned. As has 

 often been pointed out, heredity is to him equivalent to the direct trans- 

 mission of qualities from the parents to the offspring, a transmission that is 

 influenced by a vast number of external circumstances. Further, he charac- 

 terizes atavism — the recurrence of qualities similar to those of earlier 

 generations — as due to the contrast between the transmission of qualities 

 and evolution, and, moreover, he points out a number of other hereditary 

 phenomena — the transmission of qualities confined to only one sex, and the 

 inheritance of qualities that come out at some special period in life. He also 

 sought to explain that phenomenon which is now termed the "dominance" 

 of certain qualities; he calls it the "prepotency of transmission" and finds 



