Chapter III 

 THE LAMARCKIAN PRINCIPLE 



Intro- Now that we have discussed the principle of heredity and found 

 at least a provisional hypothesis to account for the origin of 

 variations, we are in a position to investigate the working of 

 Natural Selection on the material placed at its disposal. But it 

 will be well to put this off till we have seen how far Lamarck's 

 theory rests upon a sound basis. If the Lamarckian principle is 

 really at work in the world, then the part played by Natural 

 Selection is comparatively small. Lamarck, who published his 

 theory in 1 80 1, held that external conditions, such as food and 

 climate, modified the individual and that the next generation 

 inherited the modification. Exercise played a very important 

 role. 1 The giraffe's neck grew long from constant straining 

 upward ; from constant use the elephant's trunk became a long 

 and perfect grasping implement ; much desert walking made the 

 camel's foot what it is ; in each generation there was an incre- 

 ment due to exercise, and this increment was handed down to 

 the offspring. Anyone who gives much thought to the subject 

 will see some considerable difficulties standing in the way of the 

 theory. But it is still accepted by a number of biologists who, 

 though they call themselves Neo-Lamarckians, still hold with 

 little modification the theory of Lamarck. The strength of their 

 position lies in this, that they solve or attempt to solve two great 

 problems at once : (l) the origin of variations ; (2) adaptation to 

 environment. No other theory, they say, can tell us the cause 

 of variations, no other theory can explain the niceties of adapta- 

 tion that we see both in plants and animals. 



1 Will, also, according to Lamarck, was an important factor; an individual could 

 by willing modify himself. But as the will uses exercise as its means, I consider that 

 1 have included this in my statement in the text. 



