MODERN BIOLOGY 457 



already existing. He can hardly be blamed for the fact that he does not con- 

 sider that he had found any actual proof of the transition of one species to 

 another, since it has indeed scarcely been possible to discover one even in 

 our own time. He does not believe in the possibility of the various species' 

 being able to vary beyond a certain limited extent, and this limit is soon 

 reached; if we try to force a form beyond this, it perishes; as an instance he 

 quotes the adaptability of species to different climates. Man's domestic ani- 

 mals have from the beginning been especially suitable for taming, while 

 other equally or more intelligent animals, the apes, for instance, have to 

 be left at liberty. It is primarily, however, the rare existence of and sterility 

 in hybrids that to Lyell's mind gives proof of the constancy of the species. 

 The similarity between embryos of various kinds merely testifies to a com- 

 mon plan in their structure, but no common origin. He believes that every 

 species has been created in a locality suitable to it and has spread from there 

 under the constant influence of the climate, means of subsistence, and com- 

 petition with other life-forms. In disproof of Lamarck's theory of species- 

 modification he maintains that an alteration in the climatic changes or other 

 alterations in the conditions of life would give certain species advantage 

 over others, so that the adaptability assumed by Lamarck would never be 

 realized in the latter. If a lake were to be converted into a swamp, already 

 existing marsh-plants would be ready to overrun its area, while the aquatic 

 plants would die out before they had time to adapt themselves to swamp 

 conditions. How the species came to be created is a question that Lyell 

 refuses to discuss; he speaks of "creative force," though he attributes no 

 personality to it, regarding the whole problem as insoluble. Instead he dis- 

 cusses in detail the conditions governing the distribution of species, their 

 development and extinction during different geological epochs. The whole 

 of this exposition exercised a very great influence on Darwin, both positive 

 and negative, by calling forth a contradiction from him — a point on which 

 more light will be thrown later. 



But the main point is that Lyell's theory of geological evolution offered 

 at the time particularly valuable support to the idea of evolution, which 

 was one of the watchwords of the age; here indeed there was confirmation 

 in nature herself of the idea of an uninterrupted development as the funda- 

 mental force in existence. The result was that Lyell's name became one of 

 the most popular at the time, and he himself enhanced his reputation by 

 his ability to keep pace with scientific developments; he, the opponent of 

 Lamarck, associated himself directly and without reservation with Darwin. 

 His activities as the promoter of Darwinism will be dealt with in the next 

 section. 



