540 



THE CAUSES OF EVOLUTION 



lated the concept of evolution as opposed to creation, and Lamarck 

 built upon this foundation. Many of Lamarck's original ideas and 

 statements were crude and have since been ridiculed; but his 

 essential claim, that characteristics acquired by an individual in its 

 lifetime are inherited hy its offspring and thus produce evolutionary 

 changes, is the basis of the Lamarckian Theory of to-day. This 

 theory is maintained by certain biologists, who are sometimes 



called Neo-Lamarckians, since 

 they maintain the old theory 

 in a " new " guise. 



Neo-Lamarckism. — In this 

 modern form, the Lamarckian 

 Theory includes, as causes of 

 evolution, acquired charac- 

 teristics resulting from the 

 effects of use and disuse and 

 also from environment. It is 

 a familiar fact that the use of 

 muscles tends to their develop- 

 ment. The old adage " prac- 

 tice makes perfect " finds 

 many illustrations in the 

 neuromuscular coordinations 

 that are perfected by use. 

 Conversely, disuse leads to 

 deficiency or even complete 

 loss of function, as in the 

 fanatics of India who hold a 

 limb in one position until it cannot be moved. A white man who 

 lives for years in the tropics may acquire a coloration that is 

 recognizable long after his return to a temperate climate. Horses 

 that are kept in mines, and men in dungeons, have their eyes so 

 impaired that they can be restored to sight only by gradual expos- 

 ure to light, if at all. Such examples of the effects of use and dis- 

 use and of environment, which are known as " acquired charac- 

 teristics," could be cited without number among animals. We 

 have considered in an earlier chapter (c/. p. 439) the importance of 

 environmental factors in development. To this extent the con- 

 clusions of Lamarck may be modernized to express a fact that is 

 everywhere recognized. 



Fig. 296. — Georges Buffon (1707- 

 1788) scientist and popular writer who 

 has not received due credit for his early- 

 advocacy of organic evolution. 



(From Locy, "Biology and its Makers," 

 copyright, 1908, by Henry Holt & Co., 

 reprinted by permission.) 



