76 WHAT EVOLUTION IS 



as the arm of a man increases under 

 exercise. As a result of this activity 

 continued through generation after 

 generation, the neck of the giraffe 

 would lengthen and eventually reach 

 the extreme condition seen to-day. 



Both these instances involve a proc- 

 ess more complex than that in the 

 partly submerged plant, but in both 

 of them the environment is the fun- 

 damental factor. With the bird the 

 change from inland surroundings to 

 a shore environment is the important 

 element, and with the giraffe the 

 change from a region where browsing 

 was low to one where it was among 

 trees. Thus as with the plant, en- 

 vironmental differences play the chief 

 part in the evolution of these animals. 

 Put briefly, the Lamarckian scheme, 

 as applied to animals, is as follows: 

 a change in the environment is fol- 

 lowed by a change in habit, and a 



