254 Darwin, and after Darwin. 



in question consists in supposing that if any particular 

 organs in a species are habitually used for performing 

 any particular action, they must undergo a structural 

 improvement which would more and more adapt them 

 to the performance of that action ; for in each gene- 

 ration constant use would better and better adapt the 

 structures to the discharge of their functions, and they 

 would then be bequeathed to the next generation in 

 this their improved form by heredity. So that, for in- 

 stance, if there had been a thousand generations of 

 blacksmiths, we might expect the sons of the last of 

 them to inherit unusually strong arms, even if these 

 young men had themselves taken to some other trade 

 not requiring any special use of their arms. Similarly, 

 if there had been a thousand generations of men 

 who used their arms but slightly, we should expect 

 their descendants to show but a puny development of 

 the upper extremities. Now let us apply all this to the 

 animal kingdom in general. The giraffe, for instance, 

 is a ruminant whose entire frame has been adapted to 

 support an enormously long neck, which is of use to 

 the animal in reaching the foliage of trees. The an- 

 cestors of the giraffe, having had ordinary necks, were 

 supposed by Lamarck to have gradually increased the 

 length of them, through many successive generations, 

 by constantly stretching to reach high foliage ; and he 

 further supposed that, when the neck became so long 

 as to require for its support special changes in the 

 general form of the animal as a whole, these special 

 changes would have brought about the dwindling of 

 other parts from which so much activity was no longer 

 required the general result being that the whole or- 

 ganization of the animal became more and more 



