136 HEREDITY [AP. 



theories of Evolution, and thus the history of the two 

 subjects largely coincides. The first important theory 

 was that of Lamarck, published in 1809, and although 

 it had little influence at the time, in more recent 

 years Lamarck's main principle has found many sup- 

 porters. His theory was essentially that ' acquired ' 

 modifications are being continually produced and 

 perfected by every organism during its life, and that 

 they are at least partially transmitted to its offspring, 

 so that each generation will be rather better adapted 

 to its surroundings than its predecessor. In this way, 

 for example, the great length of the neck of the 

 giraffe would be explained by the continual striving 

 through many generations to reach higher leaves on 

 the trees; or the limbless condition of snakes and 

 slow-worms by the gradual loss of limbs through 

 disuse. But it has been seen that the assumption 

 that acquired characters are inherited is open to 

 grave doubt, and hence the followers of Lamarck 

 are fewer at the present time than formerly. 



Darwin's great theory of Evolution by Natural 

 Selection of course depends on quite different prin- 

 ciples, but it, like Lamarck's, is based essentially upon 

 the laws of variation and heredity. Darwin himself 

 made astonishing progress in the investigation of 

 these laws, and although he would doubtless have 

 been the first to admit the incompleteness of our 

 knowledge, yet he collected sufficient evidence to 



