264 EVOLUTION OF TO-DAY. 



the life of this generation, if the same conditions 

 remain, use will still further increase the perfection 

 of the organ, and the third generation will be better 

 endowed than the second. And so on, by continual 

 use any part will increase in size, and there will thus 

 constantly arise variations or, better, regular modifi- 

 cations in just those organs where development is 

 needed. 



This theory finds the modifying cause in the 

 activities of the organism. Any form of motion, 

 conscious or unconscious, will produce its effects. 

 But most of the motions of animals are regulated 

 by consciousness and effort on the part of the ani- 

 mal. This school, therefore, finds in the efforts of 

 the individual one of the most important factors in 

 producing variation. The statement that effort is 

 an important factor in evolution is liable to a mis- 

 understanding. It is frequently thought that the 

 theory implies that animals develop certain organs 

 because they make an effort to do so ; but this is 

 so much beyond the power of animals as we know 

 them, that it is absurd. But the theory of effort 

 and use is very different. Organs develop as the 

 result of effort, it is true, but the effort is directed 

 toward the satisfying of certain wants, and has only 

 an indirect relation to the development of the organ 

 in question. An animal has the consciousness of 

 hunger, and, in order to remove this painful feeling, 

 strives to reach the food on the branches above its 

 head. As a result from the continuation of this 

 effort and consequent strain, the neck is lengthened. 

 Or an individual endeavors to escape from its ene- 



